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Sample records for algal community structure

  1. Relations between water physico-chemistry and benthic algal communities in a northern Canadian watershed: defining reference conditions using multiple descriptors of community structure.

    PubMed

    Thomas, Kathryn E; Hall, Roland I; Scrimgeour, Garry J

    2015-09-01

    Defining reference conditions is central to identifying environmental effects of anthropogenic activities. Using a watershed approach, we quantified reference conditions for benthic algal communities and their relations to physico-chemical conditions in rivers in the South Nahanni River watershed, NWT, Canada, in 2008 and 2009. We also compared the ability of three descriptors that vary in terms of analytical costs to define algal community structure based on relative abundances of (i) all algal taxa, (ii) only diatom taxa, and (iii) photosynthetic pigments. Ordination analyses showed that variance in algal community structure was strongly related to gradients in environmental variables describing water physico-chemistry, stream habitats, and sub-watershed structure. Water physico-chemistry and local watershed-scale descriptors differed significantly between algal communities from sites in the Selwyn Mountain ecoregion compared to sites in the Nahanni-Hyland ecoregions. Distinct differences in algal community types between ecoregions were apparent irrespective of whether algal community structure was defined using all algal taxa, diatom taxa, or photosynthetic pigments. Two algal community types were highly predictable using environmental variables, a core consideration in the development of Reference Condition Approach (RCA) models. These results suggest that assessments of environmental impacts could be completed using RCA models for each ecoregion. We suggest that use of algal pigments, a high through-put analysis, is a promising alternative compared to more labor-intensive and costly taxonomic approaches for defining algal community structure. PMID:26255271

  2. Algal exudates and stream organic matter influence the structure and function of denitrifying bacterial communities.

    PubMed

    Kalscheur, Kathryn N; Rojas, Miguel; Peterson, Christopher G; Kelly, John J; Gray, Kimberly A

    2012-11-01

    Within aquatic ecosystems, periphytic biofilms can be hot spots of denitrification, and previous work has suggested that algal taxa within periphyton can influence the species composition and activity of resident denitrifying bacteria. This study tested the hypothesis that algal species composition within biofilms influences the structure and function of associated denitrifying bacterial communities through the composition of organic exudates. A mixed population of bacteria was incubated with organic carbon isolated from one of seven algal species or from one of two streams that differed in anthropogenic inputs. Pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) revealed differences in the organic composition of algal exudates and stream waters, which, in turn, selected for distinct bacterial communities. Organic carbon source had a significant effect on potential denitrification rates (DNP) of the communities, with organics isolated from a stream with high anthropogenic inputs resulting in a bacterial community with the highest DNP. There was no correlation between DNP and numbers of denitrifiers (based on nirS copy numbers), but there was a strong relationship between the species composition of denitrifier communities (as indicated by tag pyrosequencing of nosZ genes) and DNP. Specifically, the relative abundance of Pseudomonas stutzeri-like nosZ sequences across treatments correlated significantly with DNP, and bacterial communities incubated with organic carbon from the stream with high anthropogenic inputs had the highest relative abundance of P. stutzeri-like nosZ sequences. These results demonstrate a significant relationship between bacterial community composition and function and provide evidence of the potential impacts of anthropogenic inputs on the structure and function of stream microbial communities. PMID:22828897

  3. Spatial variability, structure and composition of crustose algal communities in Diadema africanum barrens

    NASA Astrophysics Data System (ADS)

    Sangil, Carlos; Sansón, Marta; Díaz-Villa, Tania; Hernández, José Carlos; Clemente, Sabrina; Afonso-Carrillo, Julio

    2014-12-01

    Crustose algal communities were studied in Diadema africanum urchin barrens around Tenerife (Canary Islands, NE Atlantic). A hierarchical nested sampling design was used to study patterns of community variability at different spatial scales (sectors, three sides of the island; sites within each sector, 5-10 km apart; stations within each site, 50-100 m apart). Although noncrustose species contributed the most to community richness, cover was dominated by crustose forms, like the coralline algae Hydrolithon farinosum, H. samoënse, H. onkodes, Neogoniolithon orotavicum and N. hirtum, and the phaeophycean Pseudolithoderma adriaticum. The structure of these communities showed high spatial variability, and we found differences in the structure of urchin barrens when compared across different spatial scales. Multivariate analysis showed that variability in community structure was related to the five environmental variables studied (wave exposure, urchin density, substrate roughness, productivity and depth). Wave exposure was the variable that contributed most to community variability, followed by urchin density and substrate roughness. Productivity and depth had limited influence. The effects of these variables differed depending on the spatial scale; wave exposure and productivity were the main variables influencing community changes at the largest scale (between different sectors of the island), while D. africanum density, roughness and depth were the most influential at medium and small scales.

  4. Seasonal inhibitory effects of marine plants on sea urchins: structuring communities the algal way.

    PubMed

    Konar, B

    2000-10-01

    Natural and manipulative experiments were used to evaluate the effect of algal cover on sea urchin (Strongylocentrotus polyacanthus) distribution on submarine pinnacles at Shemya Island in the western Aleutian Archipelago. In July, pinnacle tops had dense kelp stands with low densities of sea urchins. In subsequent months, urchin densities increased as annual algal cover declined. In the summer, removal of specific combinations of macroalgae from the pinnacle tops resulted in an increase in urchin density. Artificial structures that imitated certain common seaweeds were placed on pinnacle tops and inhibited urchin movement. Clod cards that were used to measure relative abrasion rates on vegetated and cleared pinnacles demonstrated that algae cause a significant amount of abrasion. This study showed that the physical structure of the dominant annual alga, Desmarestia viridis, is capable of limiting sea urchin distribution, movement, and grazing. In this study, a potential food source actively controlled herbivore distribution and was the primary cause for the persistence of isolated kelp communities surrounded by barrens dominated by sea urchin grazing. PMID:24595832

  5. Effect of lake water on algal biomass and microbial community structure in municipal wastewater-based lab-scale photobioreactors.

    PubMed

    Krustok, I; Truu, J; Odlare, M; Truu, M; Ligi, T; Tiirik, K; Nehrenheim, E

    2015-08-01

    Photobioreactors are a novel environmental technology that can produce biofuels with the simultaneous removal of nutrients and pollutants from wastewaters. The aim of this study was to evaluate the effect of lake water inoculation on the production of algal biomass and phylogenetic and functional structure of the algal and bacterial communities in municipal wastewater-treating lab-scale photobioreactors. Inoculating the reactors with lake water had a significant benefit to the overall algal biomass growth and nutrient reduction in the reactors with wastewater and lake water (ratio 70/30 v/v). The metagenome-based survey showed that the most abundant algal phylum in these reactors was Chlorophyta with Scenedesmus being the most prominent genus. The most abundant bacterial phyla were Proteobacteria and Bacteroidetes with most dominant families being Sphingobacteriaceae, Cytophagaceae, Flavobacteriaceae, Comamonadaceae, Planctomycetaceae, Nocardiaceae and Nostocaceae. These photobioreactors were also effective in reducing the overall amount of pathogens in wastewater compared to reactors with wastewater/tap water mixture. Functional analysis of the photobioreactor metagenomes revealed an increase in relative abundance genes related to photosynthesis, synthesis of vitamins important for auxotrophic algae and decrease in virulence and nitrogen metabolism subsystems in lake water reactors. The results of the study indicate that adding lake water to the wastewater-based photobioreactor leads to an altered bacterial community phylogenetic and functional structure that could be linked to higher algal biomass production, as well as to enhanced nutrient and pathogen reduction in these reactors. PMID:25895091

  6. Algal turf scrubber (ATS) floways on the Great Wicomico River, Chesapeake Bay: productivity, algal community structure, substrate and chemistry(1).

    PubMed

    Adey, Walter H; Laughinghouse, H Dail; Miller, John B; Hayek, Lee-Ann C; Thompson, Jesse G; Bertman, Steven; Hampel, Kristin; Puvanendran, Shanmugam

    2013-06-01

    Two Algal Turf Scrubber (ATS) units were deployed on the Great Wicomico River (GWR) for 22 months to examine the role of substrate in increasing algal productivity and nutrient removal. The yearly mean productivity of flat ATS screens was 15.4 g · m(-2)  · d(-1) . This was elevated to 39.6 g · m(-2)  · d(-1) with a three-dimensional (3-D) screen, and to 47.7 g · m(-2)  · d(-1) by avoiding high summer harvest temperatures. These methods enhanced nutrient removal (N, P) in algal biomass by 3.5 times. Eighty-six algal taxa (Ochrophyta [diatoms], Chlorophyta [green algae], and Cyan-obacteria [blue-green algae]) self-seeded from the GWR and demonstrated yearly cycling. Silica (SiO2 ) content of the algal biomass ranged from 30% to 50% of total biomass; phosphorus, nitrogen, and carbon content of the total algal biomass ranged from 0.15% to 0.21%, 2.13% to 2.89%, and 20.0% to 25.7%, respectively. Carbohydrate content (at 10%-25% of AFDM) was dominated by glucose. Lipids (fatty acid methyl ester; FAMEs) ranged widely from 0.5% to 9% AFDM, with Omega-3 fatty acids a consistent component. Mathematical modeling of algal produ-ctivity as a function of temperature, light, and substrate showed a proportionality of 4:3:3, resp-ectively. Under landscape ATS operation, substrate manipulation provides a considerable opportunity to increase ATS productivity, water quality amelioration, and biomass coproduction for fertilizers, fermentation energy, and omega-3 products. Based on the 3-D prod-uctivity and algal chemical composition demonstrated, ATS systems used for nonpoint source water treat-ment can produce ethanol (butanol) at 5.8× per unit area of corn, and biodiesel at 12.0× per unit area of soy beans (agricultural production US). PMID:27007038

  7. Influence of Diadema antillarum populations (Echinodermata: Diadematidae) on algal community structure in Jardines de la Reina, Cuba.

    PubMed

    Martín Blanco, Félix; Clero Alonso, Lídice; González Sansón, Gaspar; Amargós Fabián, Pina

    2011-09-01

    The 1983-1984 mass mortality of Diadema antillarum produced severe damages on Caribbean reefs contributing to substantial changes in community structure that still persist. Despite the importance of Diadema grazing in structuring coral reefs, available information on current abundances and algal-urchin interactions in Cuba is scarce. We analyzed spatial variations in Diadema abundance and its influence on algal community structure in 22 reef sites in Jardines de la Reina, in June/2004 and April/2005. Urchins were counted in five 30 x 2m transects per site, and algal coverage was estimated in randomly located 0.25m side quadrats (15 per site). Abundances of Diadema were higher at reef crests (0.013-1.553 ind/m2), while reef slope populations showed values up to three orders of magnitude lower and were overgrown by macroalgae (up to 87%, local values). Algal community structure at reef slopes were dominated by macroalgae, especially Dictyota, Lobophora and Halimeda while the most abundant macroalgae at reef crests were Halimeda and Amphiroa. Urchin densities were negatively and positively correlated with mean coverage of macroalgae and crustose coralline algae, respectively, when analyzing data pooled across all sites, but not with data from separate habitats (specially reef crest), suggesting, along with historical fish biomass, that shallow reef community structure is being shaped by the synergistic action of other factors (e.g. fish grazing) rather than the influence of Diadema alone. However, we observed clear signs of Diadema grazing at reef crests and decreased macroalgal cover according to 2001 data, what suggest that grazing intensity at this habitat increased at the same time that Diadema recruitment began to be noticeable. Furthermore, the excessive abundance of macroalgae at reef slopes and the scarcity of crustose coralline algae seems to be due by the almost complete absence of D. antillarum at mid depth reefs, where local densities of this urchin were

  8. Bacterial Community Structure Associated with a Dimethylsulfoniopropionate-Producing North Atlantic Algal Bloom

    PubMed Central

    González, José M.; Simó, Rafel; Massana, Ramon; Covert, Joseph S.; Casamayor, Emilio O.; Pedrós-Alió, Carlos; Moran, Mary Ann

    2000-01-01

    The bacteria associated with oceanic algal blooms are acknowledged to play important roles in carbon, nitrogen, and sulfur cycling, yet little information is available on their identities or phylogenetic affiliations. Three culture-independent methods were used to characterize bacteria from a dimethylsulfoniopropionate (DMSP)-producing algal bloom in the North Atlantic. Group-specific 16S rRNA-targeted oligonucleotides, 16S ribosomal DNA (rDNA) clone libraries, and terminal restriction fragment length polymorphism analysis all indicated that the marine Roseobacter lineage was numerically important in the heterotrophic bacterial community, averaging >20% of the 16S rDNA sampled. Two other groups of heterotrophic bacteria, the SAR86 and SAR11 clades, were also shown by the three 16S rRNA-based methods to be abundant in the bloom community. In surface waters, the Roseobacter, SAR86, and SAR11 lineages together accounted for over 50% of the bacterial rDNA and showed little spatial variability in abundance despite variations in the dominant algal species. Depth profiles indicated that Roseobacter phylotype abundance decreased with depth and was positively correlated with chlorophyll a, DMSP, and total organic sulfur (dimethyl sulfide plus DMSP plus dimethyl sulfoxide) concentrations. Based on these data and previous physiological studies of cultured Roseobacter strains, we hypothesize that this lineage plays a role in cycling organic sulfur compounds produced within the bloom. Three other abundant bacterial phylotypes (representing a cyanobacterium and two members of the α Proteobacteria) were primarily associated with chlorophyll-rich surface waters of the bloom (0 to 50 m), while two others (representing Cytophagales and δ Proteobacteria) were primarily found in deeper waters (200 to 500 m). PMID:11010865

  9. Exploring the Utilization of Complex Algal Communities to Address Algal Pond Crash and Increase Annual Biomass Production for Algal Biofuels

    SciTech Connect

    Hamilton, Cyd E.

    2014-03-25

    This white paper briefly reviews the research literature exploring complex algal communities as a means of increasing algal biomass production via increased tolerance, resilience, and resistance to a variety of abiotic and biotic perturbations occurring within harvesting timescales. This paper identifies what data are available and whether more research utilizing complex communities is needed to explore the potential of complex algal community stability (CACS) approach as a plausible means to increase biomass yields regardless of ecological context and resulting in decreased algal-based fuel prices by reducing operations costs. By reviewing the literature for what we do and do not know, in terms of CACS methodologies, this report will provide guidance for future research addressing pond crash phenomena.

  10. Effects of solar ultraviolet radiation on tropical algal communities

    SciTech Connect

    Santas, R.

    1989-01-01

    This study assessed some of the effects of solar ultraviolet (UV) radiation ion coral reef algal assemblages. The first part of the investigation was carried out under controlled laboratory conditions in the coral reef microcosm at the National Museum of Natural History in Washington, D.C., while a field counterpart was completed at the Smithsonian Institution's marine station on Grand Turk, Turks and Caicos Islands, in the eastern Caribbean. The study attempted to separate the effects of UV-A from those of UV-B. In the laboratory, algal turf assemblages exposed to simulated solar UV radiation produced 55.1% less biomass than assemblages that were not exposed to UV. Assemblages not exposed to UV were dominated by Ectocarpus rhodochondroides, whereas in the assemblage developing under high UV radiation, Enteromorpha prolifera and eventually Schizothrix calcicola dominated. Lower UV-B irradiances caused a proportional reduction in biomass production and had less pronounced effects on species composition. UV-A did not have any significant effects on either algal turf productivity or community structure. In the field, assemblages exposed to naturally occurring solar UV supported a biomass 40% lower than that of assemblages protected from UV-B exposure. Once again, UV-A did not inhibit algal turf productivity.

  11. Seasonally changing habitat use patterns among roving herbivorous fishes in the southern Red Sea: the role of temperature and algal community structure

    NASA Astrophysics Data System (ADS)

    Afeworki, Y.; Videler, J. J.; Bruggemann, J. H.

    2013-06-01

    Coral reefs are characterized by intense herbivory. Spatial patterns in herbivory—particularly along the depth gradient—influence the distribution and abundance of algae. Depth gradients in herbivorous reef fishes are generally assumed to be temporally stable, but this assumption has rarely been questioned. Here, we use underwater visual census and herbivore exclusion experiments to study the community composition and temporal patterns in habitat use by roving herbivorous fishes in an environment characterized by profound seasonal changes in algal biomass and distribution and extreme summer temperatures. Among the 18 species of roving herbivores recorded, parrotfishes were dominant in species richness and biomass, while regional endemic species represented 77 % of the total biomass. During most of the year, roving herbivores aggregate in the shallow reef zones and their biomass declines with depth. The herbivore community on the reef flat is distinct from that in deeper zones. The former is characterized by Siganus rivulatus, Acanthurus gahhm and Hipposcarus harid, while the deeper reef zones are characterized by S. ferrugineus, Chlorurus sordidus and Ctenochaetus striatus. In summer, the distinct community structures among reef zones are lost as reef flat herbivores tend to exploit deeper reef zones and some reef crest species venture on to the reef flat. This summer change in herbivore distribution is also reflected in reduced turf biomass and increased yield to herbivores in the deeper reef zones. Habitat use is related to the feeding mode such that browsers dominate the reef flat and scrapers the reef crest, while the seasonal changes correspond to changes in availability of targeted algal resources. These seasonal changes appear to be driven by the extreme temperatures in summer, reaching 36 °C on the shallow reef flat.

  12. Responses of algal communities to gradients in herbivore biomass and water quality in Marovo Lagoon, Solomon Islands

    NASA Astrophysics Data System (ADS)

    Albert, S.; Udy, J.; Tibbetts, I. R.

    2008-03-01

    Settlement tiles were used to characterise and quantify coral reef associated algal communities along water quality and herbivory gradients from terrestrial influenced near shore sites to oceanic passage sites in Marovo Lagoon, the Solomon Islands. After 6 months, settlement tile communities from inshore reefs were dominated by high biomass algal turfs (filamentous algae and cyanobacteria) whereas tiles located on offshore reefs were characterised by a mixed low biomass community of calcareous crustose algae, fleshy crustose algae and bare tile. The exclusion of macrograzers, via caging of tiles, on the outer reef sites resulted in the development of an algal turf community similar to that observed on inshore reefs. Caging on the inshore reef tiles had a limited impact on community composition or biomass. Water quality and herbivorous fish biomass were quantified at each site to elucidate factors that might influence algal community structure across the lagoon. Herbivore biomass was the dominant driver of algal community structure. Algal biomass on the other hand was controlled by both herbivory and water quality (particularly dissolved nutrients). This study demonstrates that algal communities on settlement tiles are an indicator capable of integrating the impacts of water quality and herbivory over a small spatial scale (kilometres) and short temporal scale (months), where other environmental drivers (current, light, regional variability) are constant.

  13. Disturbance frequency influences patch dynamics in stream benthic algal communities.

    PubMed

    Ledger, Mark E; Harris, Rebecca M L; Armitage, Patrick D; Milner, Alexander M

    2008-04-01

    Disturbance is integral to the organisation of riverine ecosystems. Fluctuating low flows caused by supra-seasonal drought and water management periodically dewater habitat patches, potentially creating heterogeneity in the taxonomic composition and successional dynamics of benthic communities. The frequency of disturbance induced by low flows is contingent upon the topography of the river bed and thus varies among patches. We investigated whether the frequency of patch dewatering influenced the structure and temporal dynamics of benthic algal communities attached to the upper surfaces of stones in stream mesocosms (4 m2). In a 693-day disturbance experiment, we applied short dewatering disturbances (6 days) at high (33-day cycles) and low frequencies (99-day cycles) and compared algal assemblages with undisturbed controls at 21 endpoints. In the absence of disturbance, epilithic space was dominated by the green encrusting alga Gongrosira incrustans. However, drying disturbances consistently reduced the dominance of the green alga, and crust abundance decreased with increasing disturbance frequency, thereby opening space for a diversity of mat-forming diatoms. The response of mat diatoms to disturbance varied markedly during the experiment, from strong reductions in the abundance of loosely attached mats in mid-late 2000 to the exploitation of open space by closely adhering mats in 2001. Contrary responses were attributed to changes in the species composition of mat diatoms, which influenced the physiognomy and hence stress-resistance and resilience of the assemblage. Our results indicate that patchy dewatering of habitat patches during periods of low flow influences the successional dynamics of algae, thereby creating distinctive mosaics on the stream bed. PMID:18193289

  14. Automatic identification of algal community from microscopic images.

    PubMed

    Santhi, Natchimuthu; Pradeepa, Chinnaraj; Subashini, Parthasarathy; Kalaiselvi, Senthil

    2013-01-01

    A good understanding of the population dynamics of algal communities is crucial in several ecological and pollution studies of freshwater and oceanic systems. This paper reviews the subsequent introduction to the automatic identification of the algal communities using image processing techniques from microscope images. The diverse techniques of image preprocessing, segmentation, feature extraction and recognition are considered one by one and their parameters are summarized. Automatic identification and classification of algal community are very difficult due to various factors such as change in size and shape with climatic changes, various growth periods, and the presence of other microbes. Therefore, the significance, uniqueness, and various approaches are discussed and the analyses in image processing methods are evaluated. Algal identification and associated problems in water organisms have been projected as challenges in image processing application. Various image processing approaches based on textures, shapes, and an object boundary, as well as some segmentation methods like, edge detection and color segmentations, are highlighted. Finally, artificial neural networks and some machine learning algorithms were used to classify and identifying the algae. Further, some of the benefits and drawbacks of schemes are examined. PMID:24151424

  15. Stable and sporadic symbiotic communities of coral and algal holobionts.

    PubMed

    Hester, Eric R; Barott, Katie L; Nulton, Jim; Vermeij, Mark Ja; Rohwer, Forest L

    2016-05-01

    Coral and algal holobionts are assemblages of macroorganisms and microorganisms, including viruses, Bacteria, Archaea, protists and fungi. Despite a decade of research, it remains unclear whether these associations are spatial-temporally stable or species-specific. We hypothesized that conflicting interpretations of the data arise from high noise associated with sporadic microbial symbionts overwhelming signatures of stable holobiont members. To test this hypothesis, the bacterial communities associated with three coral species (Acropora rosaria, Acropora hyacinthus and Porites lutea) and two algal guilds (crustose coralline algae and turf algae) from 131 samples were analyzed using a novel statistical approach termed the Abundance-Ubiquity (AU) test. The AU test determines whether a given bacterial species would be present given additional sampling effort (that is, stable) versus those species that are sporadically associated with a sample. Using the AU test, we show that coral and algal holobionts have a high-diversity group of stable symbionts. Stable symbionts are not exclusive to one species of coral or algae. No single bacterial species was ubiquitously associated with one host, showing that there is not strict heredity of the microbiome. In addition to the stable symbionts, there was a low-diversity community of sporadic symbionts whose abundance varied widely across individual holobionts of the same species. Identification of these two symbiont communities supports the holobiont model and calls into question the hologenome theory of evolution. PMID:26555246

  16. Variations of algal communities cause darkening of a Greenland glacier.

    PubMed

    Lutz, Stefanie; Anesio, Alexandre M; Jorge Villar, Susana E; Benning, Liane G

    2014-08-01

    We have assessed the microbial ecology on the surface of Mittivakkat glacier in SE-Greenland during the exceptional high melting season in July 2012 when the so far most extreme melting rate for the Greenland Ice Sheet has been recorded. By employing a complementary and multi-disciplinary field sampling and analytical approach, we quantified the dramatic changes in the different microbial surface habitats (green snow, red snow, biofilms, grey ice, cryoconite holes). The observed clear change in dominant algal community and their rapidly changing cryo-organic adaptation inventory was linked to the high melting rate. The changes in carbon and nutrient fluxes between different microbial pools (from snow to ice, cryoconite holes and glacial forefronts) revealed that snow and ice algae dominate the net primary production at the onset of melting, and that they have the potential to support the cryoconite hole communities as carbon and nutrient sources. A large proportion of algal cells is retained on the glacial surface and temporal and spatial changes in pigmentation contribute to the darkening of the snow and ice surfaces. This implies that the fast, melt-induced algal growth has a high albedo reduction potential, and this may lead to a positive feedback speeding up melting processes. PMID:24920320

  17. A trait-based framework for stream algal communities.

    PubMed

    Lange, Katharina; Townsend, Colin Richard; Matthaei, Christoph David

    2016-01-01

    The use of trait-based approaches to detect effects of land use and climate change on terrestrial plant and aquatic phytoplankton communities is increasing, but such a framework is still needed for benthic stream algae. Here we present a conceptual framework of morphological, physiological, behavioural and life-history traits relating to resource acquisition and resistance to disturbance. We tested this approach by assessing the relationships between multiple anthropogenic stressors and algal traits at 43 stream sites. Our "natural experiment" was conducted along gradients of agricultural land-use intensity (0-95% of the catchment in high-producing pasture) and hydrological alteration (0-92% streamflow reduction resulting from water abstraction for irrigation) as well as related physicochemical variables (total nitrogen concentration and deposited fine sediment). Strategic choice of study sites meant that agricultural intensity and hydrological alteration were uncorrelated. We studied the relationships of seven traits (with 23 trait categories) to our environmental predictor variables using general linear models and an information-theoretic model-selection approach. Life form, nitrogen fixation and spore formation were key traits that showed the strongest relationships with environmental stressors. Overall, FI (farming intensity) exerted stronger effects on algal communities than hydrological alteration. The large-bodied, non-attached, filamentous algae that dominated under high farming intensities have limited dispersal abilities but may cope with unfavourable conditions through the formation of spores. Antagonistic interactions between FI and flow reduction were observed for some trait variables, whereas no interactions occurred for nitrogen concentration and fine sediment. Our conceptual framework was well supported by tests of ten specific hypotheses predicting effects of resource supply and disturbance on algal traits. Our study also shows that investigating a

  18. Preliminary evaluation of an in vivo fluorometer to quantify algal periphyton biomass and community composition

    USGS Publications Warehouse

    Harris, Theodore D.; Graham, Jennifer

    2015-01-01

    The bbe-Moldaenke BenthoTorch (BT) is an in vivo fluorometer designed to quantify algal biomass and community composition in benthic environments. The BT quantifies total algal biomass via chlorophyll a (Chl-a) concentration and may differentiate among cyanobacteria, green algae, and diatoms based on pigment fluorescence. To evaluate how BT measurements of periphytic algal biomass (as Chl-a) compared with an ethanol extraction laboratory analysis, we collected BT- and laboratory-measured Chl-a data from 6 stream sites in the Indian Creek basin, Johnson County, Kansas, during August and September 2012. BT-measured Chl-a concentrations were positively related to laboratory-measured concentrations (R2 = 0.47); sites with abundant filamentous algae had weaker relations (R2 = 0.27). Additionally, on a single sample date, we used the BT to determine periphyton biomass and community composition upstream and downstream from 2 wastewater treatment facilities (WWTF) that discharge into Indian Creek. We found that algal biomass increased immediately downstream from the WWTF discharge then slowly decreased as distance from the WWTF increased. Changes in periphyton community structure also occurred; however, there were discrepancies between BT- and laboratory-measured community composition data. Most notably, cyanobacteria were present at all sites based on BT measurements but were present at only one site based on laboratory-analyzed samples. Overall, we found that the BT compared reasonably well with laboratory methods for relative patterns in Chl-a but not as well with absolute Chl-aconcentrations. Future studies need to test the BT over a wider range of Chl-aconcentrations, in colored waters, and across various periphyton assemblages.

  19. In-depth characterization of wastewater bacterial community in response to algal growth using pyrosequencing.

    PubMed

    Lee, Jangho; Lee, Juyoun; Lee, Tae Kwon; Woo, Sung-Geun; Baek, Gyu Seok; Park, Joonhong

    2013-10-28

    Microalgae have been regarded as a natural resource for sustainable materials and fuels, as well as for removal of nutrients and micropollutants from wastewater, and their interaction with bacteria in wastewater is a critical factor to consider because of the microbial diversity and complexity in a variety of wastewater conditions. Despite their importance, very little is known about the ecological interactions between algae and bacteria in a wastewater environment. In this study, we characterized the wastewater bacterial community in response to the growth of a Selenastrum gracile UTEX 325 population in a real municipal wastewater environment. The Roche 454 GS-FLX Titanium pyrosequencing technique was used for indepth analysis of amplicons of 16S rRNA genes from different conditions in each reactor, with and without the algal population. The algal growth reduced the bacterial diversity and affected the bacterial community structure in the wastewater. The following in-depth analysis of the deep-sequenced amplicons showed that the algal growth selectively stimulated Sphingobacteria class members, especially the Sediminibacterium genus population, in the municipal wastewater environment. PMID:23867704

  20. A catchment-scale palaeolimnological investigation into multiple forcings of algal community change

    NASA Astrophysics Data System (ADS)

    Moorhouse, H. L.; McGowan, S.; Jones, M.; Brayshaw, S.; Barker, P.; Leavitt, P.

    2013-12-01

    A catchment-scale palaeolimnological investigation of sedimentary algal pigments spanning the past ~200 years was undertaken on lakes which drain into Windermere, England's largest and longest lake. We aimed to determine the relative influence of past regional (climatic, atmospheric deposition) and local (land-use, hydrological modification, point-source pollution) drivers of algal community change by comparing three fertile lowland lakes (Blelham Tarn, Esthwaite Water and Rydal Water) and two upland tarns (Stickle and Easedale Tarns) to better inform a catchment-wide management strategy for Windermere. Drivers of change at the upland sites included atmospheric acid deposition, climatic change and structural modifications caused by dam installation, whereas the influence of agriculture and point-source pollution is greater in the lakes in the lowland parts of the catchment. As a result, contrasting algal responses were noted in the lakes. For example, the cyanobacterial pigment zeaxanthin and the cryptophte pigment alloxanthin increased at Stickle Tarn (359% and 321% respectively) corresponding with the establishment of a dam at the outflow of the tarn in 1838. However, post-1900's the concentration of these pigments declined both at Stickle and at Easedale Tarn coincident with increased storm events and in the later decades of the century (~1980s onwards) decreases in acid deposition. In the lowland sites the cyanobacterial pigment aphanizophyll increased by 400-7000% and the indicator of total algal production β-carotene increased as much as six-fold indicating a substantial degradation in water quality and the onset of cyanobacterial blooms since the 1950's. In the lowland sites, degradation of water quality was closely linked to sewage installations and treatment work upgrades during the 1950's-70's and intensification of agricultural practices most notably increases in sheep stocking densities, which expanded in the 1950's. In lowland lakes with a higher

  1. The response of the Benthic Algal Community of Saginaw Bay, near the Charity Islands, to changes in light penetration

    SciTech Connect

    Litteral, R.L.; Pillsbury, R.W.; Lowe, R.L.

    1995-06-01

    The spread of the zebra mussel (Dreissena polymorpha) into the Great Lakes has been associated with changes in water clarity. Mussel colonies, as dense as 115,000/m{sup 2}, remove large amounts of phytoplankton from the water column, resulting in significant increases in light penetration to the benthos. Saginaw Bay, Lake Huron is an area that has recently been inundated by zebra mussels. While the first mussels appeared in the summer of 1991, they now dominate nearly the entire bay. A study site was chosen two kilometers north of Charity Island in Saginaw Bay. To assess the impact of changing light intensity on the benthic algal community, light was manipulated by covering the tops of cages with shade cloth, which reduced light penetration by 58%. Natural rock substrates were used. Our data show that this is similar to light penetration prior to zebra mussels infestation. Algal community composition was determined and biovolumes were calculated to assess changes in community structure and population shifts. Our 1993 results indicate a trend of increasing dominance by green algae, with diatoms favoring pre-Dreissena light conditions. Results also indicate that green filaments that composed 93% of the community structure in 1993 are not present in 1994. Green algal biovolume for 1994 comprised 29% of the community structure, a decrease from 94% in 1993. These changes are accompanied by increases in diatom biovolume and decreasing light penetration in 1994.

  2. Effect of Tetracycline Antibiotics on Performance and Microbial Community of Algal Photo-Bioreactor.

    PubMed

    Taşkan, Ergin

    2016-07-01

    Tetracycline antibiotics have been increasingly used in medical applications and have been found in wastewater treatment plants as a result of human and industrial activities. This study investigates the combined effects of tetracycline antibiotics on the performance of an algal photo-bioreactor operated under different antibiotic concentrations in the ranges of 0.25 to 30 mg/L and considers the inhibition of algal growth, carbon and nutrient removal rates, and eukaryotic and cyanobacterial algal community changes. The results indicated that increases in the concentration of tetracycline mixtures have adverse effects on the algal community and the performance of a photo-bioreactor, and the eukaryotic algae species were more sensitive to tetracycline antibiotics than were the cyanobacterial species. Cultivation tests showed that approximately 94 % growth inhibition of mixed algae occurred at 30 mg/L. PMID:26961083

  3. Micro-structured surfaces for algal biofilm growth

    NASA Astrophysics Data System (ADS)

    Sathananthan, Suthamathy; Genin, Scott N.; Aitchison, J. Stewart; Allen, D. Grant

    2013-12-01

    It is well known that cells respond to structured surface cues that are on the micro/nanometer scale. Tissue engineering and bio-fouling fields have utilized the semiconductor device fabrication processes to make micro- and nanometer patterned surfaces to study animal cell tissue formation and to prevent algae attachment on marine surfaces respectively. In this paper we describe the use of micro-structured surfaces to study the attachment and growth of algal films. This paper gives an overview of how micro-structured surfaces are made for this purpose, how they are incorporated into a photo bioreactor and how this patterning influences the growth of an algal biofilm. Our results suggest that surface patterning with deeper V-groove patterns that are of the same size scale as the algal species has resulted in higher biomass productivity giving them a chance to embed and attach on the slope and flat surfaces whereas shallower size grooves and completely flat surfaces did not show this trend.

  4. Stressor-Response Models Relating Nutrient Enrichment to Algal Communities in Pacific Northwest Streams and Rivers

    NASA Astrophysics Data System (ADS)

    Sobota, D. J.; Hubler, S.; Paul, M. J.; Labiosa, R.

    2015-12-01

    Excessive algal growth in streams and rivers from nutrient enrichment can cause costly human health and environmental problems. As part of the US Environmental Protection Agency's Nutrient Scientific Technical Exchange Partnership and Support (N-STEPS) program, we have been developing stressor-response (S-R) models relating nutrients to attached algal (periphyton) communities to help prioritize monitoring for water quality impairments in Oregon (Pacific Northwest, USA) streams and rivers. Existing data from the state and neighboring states were compiled and standardized from the Oregon Department of Environmental Quality, US Environmental Protection Agency, and the US Geological Survey. To develop S-R models, algal community and biomass metrics were compared with nitrogen (N) and phosphorus (P) concentration data, including total, dissolved, and inorganic forms of these nutrients. In total, 928 paired algal-nutrient samples were compiled from the 8 Level-III Ecoregions occurring in Oregon. Relationships between algal biomass metrics and nutrient concentrations were weak, with only ash-free dry mass and standing stock of chlorophyll a showing slight positive relationships across gradients of total N and soluble reactive P concentrations, respectively. In contrast, metrics describing algal community composition, including percent diatoms and abundance of nutrient-sensitive species, showed very strong nonlinear relationships with total N or P concentrations. This suggests that data describing algal community composition can help identify specific nutrient stressors across environmentally-diverse streams and rivers in the Pacific Northwest. Future analyses will examine if nutrient-algal S-R models vary across different hydrological, physiographical, and ecological settings in the region.

  5. Two coexisting tank bromeliads host distinct algal communities on a tropical inselberg.

    PubMed

    Carrias, J-F; Céréghino, R; Brouard, O; Pélozuelo, L; Dejean, A; Couté, A; Corbara, B; Leroy, C

    2014-09-01

    The tank bromeliads Aechmea aquilega (Salisb.) and Catopsis berteroniana (Schultes f.) coexist on a sun-exposed Neotropical inselberg in French Guiana, where they permit conspicuous freshwater pools to form that differ in size, complexity and detritus content. We sampled the algal communities (both eukaryotic and cyanobacterial taxa, including colourless forms) inhabiting either A. aquilega (n = 31) or C. berteroniana (n = 30) and examined differences in community composition and biomass patterns in relation to several biotic and abiotic variables. Chlorella sp. and Bumilleriopsis sp. were the most common taxa and dominated the algal biomass in A. aquilega and C. berteroniana, respectively. Using a redundancy analysis, we found that water volume, habitat complexity and the density of phagotrophic protozoa and collector-gatherer invertebrates were the main factors explaining the distribution of the algal taxa among the samples. Hierarchical clustering procedures based on abundance and presence/absence data clearly segregated the samples according to bromeliad species, revealing that the algal communities in the smaller bromeliad species were not a subset of the communities found in the larger bromeliad species. We conclude that, even though two coexisting tank bromeliad populations create adjacent aquatic habitats, each population hosts a distinct algal community. Hence, bromeliad diversity is thought to promote the local diversity of freshwater algae in the Neotropics. PMID:24400863

  6. Seasonal variations of epipelic algal community in relation to environmental factors in the Istanbul Strait (the Bosphorus), Turkey.

    PubMed

    Aktan, Y; Balkıs, N; Balkıs, N

    2014-04-15

    This study was implemented to investigate the species composition, abundance, seasonal variations and diversity of epipelic algae, to determine environmental variables affecting them and to reveal the accumulation of total organic carbon in the sediment in the coastal zone of the Istanbul Strait, Turkey. Epipelic algal community consisted of 44 taxa with a low diversity. The sediment structure which is highly unstable due to the high hydrodynamism of the zone played a dominant role as the main factor in the epipelic algal flora along the coasts of Istanbul Strait. Low TOC and high carbonate values also support this result. The dominance of cyanobacteria in some periods and, as a result of this, the record of the lowest diversity index values indicated the effect of nutrient enrichment and the risk of coastal eutrophication. High dominance of cyanobacteria may also be explicated by climate changes considering its effect in the other areas. PMID:24467854

  7. Nitrogen fixation rates in algal turf communities of a degraded versus less degraded coral reef

    NASA Astrophysics Data System (ADS)

    den Haan, Joost; Visser, Petra M.; Ganase, Anjani E.; Gooren, Elfi E.; Stal, Lucas J.; van Duyl, Fleur C.; Vermeij, Mark J. A.; Huisman, Jef

    2014-12-01

    Algal turf communities are ubiquitous on coral reefs in the Caribbean and are often dominated by N2-fixing cyanobacteria. However, it is largely unknown (1) how much N2 is actually fixed by turf communities and (2) which factors affect their N2 fixation rates. Therefore, we compared N2 fixation activity by turf communities at different depths and during day and night-time on a degraded versus a less degraded coral reef site on the island of Curaçao. N2 fixation rates measured with the acetylene reduction assay were slightly higher in shallow (5-10-m depth) than in deep turf communities (30-m depth), and N2 fixation rates during the daytime significantly exceeded those during the night. N2 fixation rates by the turf communities did not differ between the degraded and less degraded reef. Both our study and a literature survey of earlier studies indicated that turf communities tend to have lower N2 fixation rates than cyanobacterial mats. However, at least in our study area, turf communities were more abundant than cyanobacterial mats. Our results therefore suggest that turf communities play an important role in the nitrogen cycle of coral reefs. N2 fixation by turfs may contribute to an undesirable positive feedback that promotes the proliferation of algal turf communities while accelerating coral reef degradation.

  8. Relationships between primary production and irradiance in coral reef algal communities

    SciTech Connect

    Not Available

    1985-07-01

    Shallow water algal turf communities are the major primary producers on coral reefs. High rates of primary production are maintained despite extremely high light intensities and exposure to ultraviolet wavelengths. The relationships between the light intensity and primary production in these assemblages are typical of algae adapted to a high light environment (low ..cap alpha.. (initial slope), high I/sub k/ (saturating light intensity), and high I/sub c/ (compensation point light intensity)). Seasonal variations in algal standing crop due to herbivory and daylength result in some characteristic photoadaptive changes in ..cap alpha.. I/sub k/, and I/sub c/ and changes in Pnet/sub max/ rates (maximum net photosynthetic rate achieved at light saturation) on both a chlorophyll ..cap alpha.. and an areal basis. Exposure to UV wavelength results in significantly higher respiration rates but no changes in ..cap alpha.., Pnet/sub max/, or I/sub k/, when compared with these parameters for the same algal communities incubated at the same light intensities without UV wavelengths. The apparent lack of photoinhibition in these algae allows calculation of the daily integrated production from the P vs. I parameters. This integrated production is highest in July (3.1 +/- 0.2 g C m/sup -2/d/sup -1/) and is reduced by 30% from this maximum in December (2.1 +/- 0.1 g C m/sup -2/d/sup -1/).

  9. Changes in soil algal communities in spruce phytocenoses under the influence of aerotechnogenic pollution

    NASA Astrophysics Data System (ADS)

    Novakovskaya, I. V.; Patova, E. N.

    2007-05-01

    The regularities of the development of algal communities in podzolic soils under coniferous forests were studied in areas differing in their technogenic pollution intensity. In the unpolluted soils under spruce forests, 80 alga species of 6 divisions were found; in the soils under the coniferous forests located in the zone exposed to the technogenic pollution, 59 alga species of 5 divisions were found. The algal groups in the soils of the spruce forests included 14 48 taxa. Chlamydomonas gloeogama, C. reinhardtii, Chlorella vulgaris, Klebsormidium nitens, and Stichococcus bacillaris were resistant to different anthropogenic impacts. The results obtained may be used for monitoring of the state of the soil biota in the soils under the boreal forests of protected areas and also in spruce forests exposed to intense aerial technogenic pollution.

  10. Bayesian Modeling of the Effects of Extreme Flooding and the Grazer Community on Algal Biomass Dynamics in a Monsoonal Taiwan Stream.

    PubMed

    Chiu, Ming-Chih; Kuo, Mei-Hwa; Chang, Hao-Yen; Lin, Hsing-Juh

    2016-08-01

    The effects of grazing and climate change on primary production have been studied widely, but seldom with mechanistic models. We used a Bayesian model to examine the effects of extreme weather and the invertebrate grazer community on epilithic algal biomass dynamics over 10 years (from January 2004 to August 2013). Algal biomass and the invertebrate grazer community were monitored in the upstream drainage of the Dajia River in Taiwan, where extreme floods have been becoming more frequent. The biomass of epilithic algae changed, both seasonally and annually, and extreme flooding changed the growth and resistance to flow detachment of the algae. Invertebrate grazing pressure changes with the structure of the invertebrate grazer community, which, in turn, is affected by the flow regime. Invertebrate grazer community structure and extreme flooding both affected the dynamics of epilithic algae, but in different ways. Awareness of the interactions between algal communities and grazers/abiotic factors can help with the design of future studies and could facilitate the development of management programs for stream ecosystems. PMID:27273089

  11. An Application of Lagrangian Coherent Structures to Harmful Algal Blooms

    NASA Astrophysics Data System (ADS)

    Olascoaga, M. J.; Beron-Vera, F. J.; Brand, L. E.; Kocak, H.

    2009-04-01

    Karenia brevis is present in low concentrations in vast areas of the Gulf of Mexico (GoM). This toxic dinoflagellate sporadically develops blooms anywhere in the GoM, except in the southern portion of West Florida Shelf (WFS). There, these harmful algal blooms (HABs) are recurrent events whose frequency and intensity are increasing. HABs on the WFS are usually only evident once they have achieved high concentrations that can be detected by observation of discolored water, which may be apparent in satellite imagery; by ecological problems such as fish kills; or human health problems. Because the early development stages of HABs are usually not detected, there is limited understanding of the environmental conditions that lead to their development. Analysis of simulated surface ocean currents reveals the presence of a persistent large-scale Lagrangian coherent structure (LCS) on the southern portion of the WFS. A LCS can be regarded as a distinguished material line which divides immiscible fluid regions with distinct advection properties. Consistent with satellite-tracked drifter trajectories, this LCS on the WFS constitutes a cross-shelf barrier for the lateral transport of passive tracers. We hypothesize that such a LCS provides favorable conditions for the development of HABs. LCSs are also employed to trace the early location of an observed HAB on the WFS. Using a simplified population dynamics model we infer the factors that could possibly lead to the development of this HAB. The population dynamics model determines nitrogen in two components, nutrients and phytoplankton, which are assumed to be passively advected by simulated surface ocean currents. Two nutrient sources are inferred for the HAB whose evolution is found to be strongly tied to the simulated LCSs. These nutrient sources are found to be located near shore and likely due to land runoff.

  12. Influence of global change-related impacts on the mercury toxicity of freshwater algal communities.

    PubMed

    Val, Jonatan; Muñiz, Selene; Gomà, Joan; Navarro, Enrique

    2016-01-01

    The climatic-change related increase of temperatures, are expected to alter the distribution and survival of freshwater species, ecosystem functions, and also the effects of toxicants to aquatic biota. This study has thus assessed, as a first time, the modulating effect of climate-change drivers on the mercury (Hg) toxicity of freshwater algal photosynthesis. Natural benthic algal communities (periphyton) have been exposed to Hg under present and future temperature scenarios (rise of 5 °C). The modulating effect of other factors (also altered by global change), as the quality and amount of suspended and dissolved materials in the rivers, has been also assessed, exposing algae to Hg in natural river water or a synthetic medium. The EC50 values ranged from the 0.15-0.74 ppm for the most sensitive communities, to the 24-40 ppm for the most tolerant. The higher tolerance shown by communities exposed to higher Hg concentrations, as Jabarrella was in agreement with the Pollution Induced Community Tolerance concept. In other cases, the dominance of the invasive diatom Didymosphenia geminata explained the tolerance or sensitivity of the community to the Hg toxicity. Results shown that while increases in the suspended solids reduced Hg bioavailability, changes in the dissolved materials - such as organic carbon - may increase it and thus its toxic effects on biota. The impacts of the increase of temperatures on the toxicological behaviour of periphyton (combining both changes at species composition and physiological acclimation) would be certainly modulated by other effects at the land level (i.e., alterations in the amount and quality of dissolved and particulate substances arriving to the rivers). PMID:26024757

  13. Stress-Survival Gene Identification From an Acid Mine Drainage Algal Mat Community

    NASA Astrophysics Data System (ADS)

    Urbina-Navarrete, J.; Fujishima, K.; Paulino-Lima, I. G.; Rothschild-Mancinelli, B.; Rothschild, L. J.

    2014-12-01

    Microbial communities from acid mine drainage environments are exposed to multiple stressors to include low pH, high dissolved metal loads, seasonal freezing, and desiccation. The microbial and algal communities that inhabit these niche environments have evolved strategies that allow for their ecological success. Metagenomic analyses are useful in identifying species diversity, however they do not elucidate the mechanisms that allow for the resilience of a community under these extreme conditions. Many known or predicted genes encode for protein products that are unknown, or similarly, many proteins cannot be traced to their gene of origin. This investigation seeks to identify genes that are active in an algal consortium during stress from living in an acid mine drainage environment. Our approach involves using the entire community transcriptome for a functional screen in an Escherichia coli host. This approach directly targets the genes involved in survival, without need for characterizing the members of the consortium.The consortium was harvested and stressed with conditions similar to the native environment it was collected from. Exposure to low pH (< 3.2), high metal load, desiccation, and deep freeze resulted in the expression of stress-induced genes that were transcribed into messenger RNA (mRNA). These mRNA transcripts were harvested to build complementary DNA (cDNA) libraries in E. coli. The transformed E. coli were exposed to the same stressors as the original algal consortium to select for surviving cells. Successful cells incorporated the transcripts that encode survival mechanisms, thus allowing for selection and identification of the gene(s) involved. Initial selection screens for freeze and desiccation tolerance have yielded E. coli that are 1 order of magnitude more resistant to freezing (0.01% survival of control with no transcript, 0.2% survival of E. coli with transcript) and 3 orders of magnitude more resistant to desiccation (0.005% survival of

  14. [Changes of algal communities in water body with different proportions of nitrogen and phosphorus].

    PubMed

    Sun, Ling; Jin, Xiangcan; Zhong, Yuan; Zhang, Dongmei; Zhu, Lin; Dai, Shugui; Zhuang, Yuanyi

    2006-07-01

    A simulation test was conducted in aquaria to study the responses of algal communities to different N/P ratios in urban water body. The water sample was taken from a small artificial lake in Tianjin, and its initial N/P ratio was adjusted to 0. 5:1,7.2:1, 25:1 and 50:1, respectively. The results showed that in high N/P ratio groups, the numbers of Chlorophyta species decreased, while those of Cyanophyta species didn' t change very much. The numbers of these two species were both decreased in low N/P ratio group. Algal biomass, cell density and chlorophyll a content in medium and high N groups were higher than those in control and high P groups. The mean value of chlorophyll a reached the highest (69.7 microg x L(-1)) in high N group, and was 54.3, 30.3 and 29.7 microg x L(-1) in medium N, control, and high P groups, respectively. At the mid-late stages of culture, green algae Dictyosphaerium pulchellum was dominant in high P group, while blue algae Phormidium tenue, P. corium, Lyngbya limnetica and Microcystis aeruginosa were dominated in high N/P ratio groups. Control group had the highest species richness, while medium and high N groups had the highest and lowest ecological species dominance, respectively. PMID:17044495

  15. Genetic diversity in marine algal virus communities as revealed by sequence analysis of DNA polymerase genes.

    PubMed Central

    Chen, F; Suttle, C A; Short, S M

    1996-01-01

    Algal-virus-specific PCR primers were used to amplify DNA polymerase gene (pol) fragments (683 to 689 bp) from the virus-sized fraction (0.02 to 0.2 microns) concentrated from inshore and offshore water samples collected from the Gulf of Mexico. Algal-virus-like DNA pol genes were detected in five samples collected from the surface and deep chlorophyll maximum. PCR products from an offshore station were cloned, and the genetic diversity of 33 fragments was examined by restriction fragment length polymorphism and sequence analysis. The five different genotypes or operational taxonomic units (OTUs) that were identified on the basis of restriction fragment length polymorphism banding patterns were present in different relative abundances (9 to 34%). One clone from each OTU was sequenced, and phylogenetic analysis showed that all of the OTUs fell within the family Phycodnaviridae. Four of the OTUs fell within a group of viruses (MpV) which infect the photosynthetic picoplankter Micromonas pusilla. The genetic diversity among these genotypes was as large as that previously found for MpV isolates from different oceans. The remaining genotype formed its own clade between viruses which infect M. pusilla and Chrysochromulina brevifilum. These results imply that marine virus communities contain a diverse assemblage of MpV-like viruses, as well as other unknown members of the Phycodnaviridae. PMID:8702280

  16. Seasonal patterns in stream periphyton fatty acids and community benthic algal composition in six high quality headwater streams

    USGS Publications Warehouse

    Honeyfield, Dale C.; Maloney, Kelly O.

    2015-01-01

    Fatty acids are integral components of periphyton and differ among algal taxa. We examined seasonal patterns in periphyton fatty acids in six minimally disturbed headwater streams in Pennsylvania’s Appalachian Mountains, USA. Environmental data and periphyton were collected across four seasons for fatty acid and algal taxa content. Non-metric multidimensional scaling ordination suggested significant seasonal differences in fatty acids; an ordination on algal composition revealed similar seasonal patterns, but with slightly weaker separation of summer and fall. Summer and fall fatty acid profiles were driven by temperature, overstory cover, and conductivity and winter profiles by measures of stream size. Ordination on algal composition suggested that summer and fall communities were driven by overstory and temperature, whereas winter communities were driven by velocity. The physiologically important fatty acid 18:3ω6 was highest in summer and fall. Winter samples had the highest 20:3ω3. Six saturated fatty acids differed among the seasons. Periphyton fatty acids profiles appeared to reflect benthic algal species composition. This suggests that periphyton fatty acid composition can be useful in characterizing basal food resources and stream water quality.

  17. Water-quality parameters and benthic algal communities at selected streams in Minnesota, August 2000 - Study design, methods and data

    USGS Publications Warehouse

    Lee, K.E.

    2002-01-01

    This report describes the study design, sampling methods, and summarizes the physical, chemical, and benthic algal data for a component of the multiagency study that was designed to document diurnal water-quality measurements (specific conductance, pH, water temperature, and dissolved oxygen), benthic algal community composition and chlorophyll-a content, and primary productivity at 12 stream sites on 6 streams in Minnesota during August 2000. Specific conductance, pH, water temperature, dissolved oxygen concentrations and percent dissolved oxygen saturation measurements were made with submersible data recorders at 30 minute intervals for a period of 3-6 days during August 2000. Benthic algae collected from wood and rock substrate were identified and enumerated. Biovolume (volume of algal cells per unit area), density (number of cells per unit area), and chlorophyll-a content from benthic algae were determined. These data can be used as part of the multiagency study to develop an understanding of the relations among nutrient concentrations, algal abundance, algal community composition, and primary production and respiration processes in rivers of differing ecoregions in Minnesota.

  18. Predicting algal growth inhibition toxicity: three-step strategy using structural and physicochemical properties.

    PubMed

    Furuhama, A; Hasunuma, K; Hayashi, T I; Tatarazako, N

    2016-05-01

    We propose a three-step strategy that uses structural and physicochemical properties of chemicals to predict their 72 h algal growth inhibition toxicities against Pseudokirchneriella subcapitata. In Step 1, using a log D-based criterion and structural alerts, we produced an interspecies QSAR between algal and acute daphnid toxicities for initial screening of chemicals. In Step 2, we categorized chemicals according to the Verhaar scheme for aquatic toxicity, and we developed QSARs for toxicities of Class 1 (non-polar narcotic) and Class 2 (polar narcotic) chemicals by means of simple regression with a hydrophobicity descriptor and multiple regression with a hydrophobicity descriptor and a quantum chemical descriptor. Using the algal toxicities of the Class 1 chemicals, we proposed a baseline QSAR for calculating their excess toxicities. In Step 3, we used structural profiles to predict toxicity either quantitatively or qualitatively and to assign chemicals to the following categories: Pesticide, Reactive, Toxic, Toxic low and Uncategorized. Although this three-step strategy cannot be used to estimate the algal toxicities of all chemicals, it is useful for chemicals within its domain. The strategy is also applicable as a component of Integrated Approaches to Testing and Assessment. PMID:27171903

  19. Harmful algal blooms (HABs), dissolved organic matter (DOM), and planktonic microbial community dynamics at a near-shore and a harbour station influenced by upwelling (SW Iberian Peninsula)

    NASA Astrophysics Data System (ADS)

    Loureiro, Sofia; Reñé, Albert; Garcés, Esther; Camp, Jordi; Vaqué, Dolors

    2011-05-01

    The surface microalgal community, including harmful species, dissolved organic matter (DOM), and bacterial and viral populations were studied during an annual cycle (November 2007-October 2008) in a Near-shore (NS) and a Harbour (H) station located in an upwelling area (Sagres, SW Iberian Peninsula). The higher water residence time, water stability and shallowness of harbours in comparison with open waters likely contributed to the differences found between stations regarding chemical variables, statistical correlations and harmful algal proliferations. Also, several differences were noticed from a previous assessment ( Loureiro et al., 2005) including higher SST, lower nitrate and chlorophyll a concentrations, along with a shift in the microplankton community structure from diatom to nanoflagellate predominance. These variations feasibly reflect the response of this dynamic system to regional environmental modifications contributing to the understanding of common patterns in environmental change trends. The division of the sampling period into (1) non-upwelling (Non-Uw), (2) "spin-up" of upwelling (SU-Uw), and (3) "spin-down" and relaxation-downwelling (SD-Rel) stages allowed the identification of natural groupings of microplankton samples by Multi Dimensional Scaling (MDS) analysis. Dissolved organic nitrogen (DON) and viruses were the most significant abiotic and biotic variables, respectively, contributing to the dissimilarities between these stages (SIMPER analysis) and, therefore, potentially affecting the microplankton community structure. Harmful algal species and a stable viral community appeared to be favoured by SD-Rel conditions. Data seem to indicate that both Gymnodinium catenatum and Heterosigma akashiwo, the most abundant potentially harmful species, have been imported into the sampling area. Also, the H location, together with potential retention sites developing around the Cabo de São Vicente upwelling centre, may contribute to the local

  20. Algal and Invertebrate Community Composition along Agricultural Gradients: A Comparative Study from Two Regions of the Eastern United States

    USGS Publications Warehouse

    Calhoun, Daniel L.; Gregory, M. Brian; Weyers, Holly S.

    2008-01-01

    Benthic algal and invertebrate communities in two Coastal Plain regions of the Eastern United States?the Delmarva Peninsula (27 sites) and Georgia Upper Coastal Plain (29 sites)?were assessed to determine if aspects of agricultural land use and nutrient conditions (dissolved and whole-water nitrogen and phosphorus) could be linked to biological community compositions. Extensive effort was made to compile land-use data describing the basin and riparian conditions at multiple scales to determine if scale played a role in these relations. Large differences in nutrient condition were found between the two study areas, wherein on average, the Delmarva sites had three times the total phosphorus and total nitrogen as did the sites in the Georgia Upper Coastal Plain. A statistical approach was undertaken that included multivariate correlations between Bray-Curtis similarity matrices of the biological communities and Euclidean similarity matrices of instream nutrients and land-use categories. Invertebrate assemblage composition was most associated with land use near the sampled reach, and algal diatom assemblage composition was most associated with land use farther from the streams and into the watersheds. Link tree analyses were conducted to isolate portions of nonmetric multidimensional scaling ordinations of community compositions that could be explained by break points in abiotic datasets. Invertebrate communities were better defined by factors such as agricultural land use near streams and geographic position. Algal communities were better defined by agricultural land use at the basin scale and instream nutrient chemistry. Algal autecological indices were more correlated with gradients of nutrient condition than were typically employed invertebrate metrics and may hold more promise in indicating nutrient impairment in these regions. Nutrient conditions in the respective study areas are compared to draft nutrient criteria established by the U.S. Environmental Protection

  1. Coral–algal phase shifts alter fish communities and reduce fisheries production

    PubMed Central

    Ainsworth, Cameron H; Mumby, Peter J

    2015-01-01

    Anthropogenic stress has been shown to reduce coral coverage in ecosystems all over the world. A phase shift towards an algae-dominated system may accompany coral loss. In this case, the composition of the reef-associated fish assemblage will change and human communities relying on reef fisheries for income and food security may be negatively impacted. We present a case study based on the Raja Ampat Archipelago in Eastern Indonesia. Using a dynamic food web model, we simulate the loss of coral reefs with accompanied transition towards an algae-dominated state and quantify the likely change in fish populations and fisheries productivity. One set of simulations represents extreme scenarios, including 100% loss of coral. In this experiment, ecosystem changes are driven by coral loss itself and a degree of habitat dependency by reef fish is assumed. An alternative simulation is presented without assumed habitat dependency, where changes to the ecosystem are driven by historical observations of reef fish communities when coral is lost. The coral–algal phase shift results in reduced biodiversity and ecosystem maturity. Relative increases in the biomass of small-bodied fish species mean higher productivity on reefs overall, but much reduced landings of traditionally targeted species. PMID:24953835

  2. Coral-algal phase shifts alter fish communities and reduce fisheries production.

    PubMed

    Ainsworth, Cameron H; Mumby, Peter J

    2015-01-01

    Anthropogenic stress has been shown to reduce coral coverage in ecosystems all over the world. A phase shift towards an algae-dominated system may accompany coral loss. In this case, the composition of the reef-associated fish assemblage will change and human communities relying on reef fisheries for income and food security may be negatively impacted. We present a case study based on the Raja Ampat Archipelago in Eastern Indonesia. Using a dynamic food web model, we simulate the loss of coral reefs with accompanied transition towards an algae-dominated state and quantify the likely change in fish populations and fisheries productivity. One set of simulations represents extreme scenarios, including 100% loss of coral. In this experiment, ecosystem changes are driven by coral loss itself and a degree of habitat dependency by reef fish is assumed. An alternative simulation is presented without assumed habitat dependency, where changes to the ecosystem are driven by historical observations of reef fish communities when coral is lost. The coral-algal phase shift results in reduced biodiversity and ecosystem maturity. Relative increases in the biomass of small-bodied fish species mean higher productivity on reefs overall, but much reduced landings of traditionally targeted species. PMID:24953835

  3. A community change in the algal endosymbionts of a scleractinian coral following a natural bleaching event: field evidence of acclimatization

    PubMed Central

    Jones, A.M; Berkelmans, R; van Oppen, M.J.H; Mieog, J.C; Sinclair, W

    2008-01-01

    The symbiosis between reef-building corals and their algal endosymbionts (zooxanthellae of the genus Symbiodinium) is highly sensitive to temperature stress, which makes coral reefs vulnerable to climate change. Thermal tolerance in corals is known to be substantially linked to the type of zooxanthellae they harbour and, when multiple types are present, the relative abundance of types can be experimentally manipulated to increase the thermal limits of individual corals. Although the potential exists for this to translate into substantial thermal acclimatization of coral communities, to date there is no evidence to show that this takes place under natural conditions. In this study, we show field evidence of a dramatic change in the symbiont community of Acropora millepora, a common and widespread Indo-Pacific hard coral species, after a natural bleaching event in early 2006 in the Keppel Islands (Great Barrier Reef). Before bleaching, 93.5% (n=460) of the randomly sampled and tagged colonies predominantly harboured the thermally sensitive Symbiodinium type C2, while the remainder harboured a tolerant Symbiodinium type belonging to clade D or mixtures of C2 and D. After bleaching, 71% of the surviving tagged colonies that were initially C2 predominant changed to D or C1 predominance. Colonies that were originally C2 predominant suffered high mortality (37%) compared with D-predominant colonies (8%). We estimate that just over 18% of the original A. millepora population survived unchanged leaving 29% of the population C2 and 71% D or C1 predominant six months after the bleaching event. This change in the symbiont community structure, while it persists, is likely to have substantially increased the thermal tolerance of this coral population. Understanding the processes that underpin the temporal changes in symbiont communities is key to assessing the acclimatization potential of reef corals. PMID:18348962

  4. From benchtop to raceway : spectroscopic signatures of dynamic biological processes in algal communities.

    SciTech Connect

    Trahan, Christine Alexandra; Garcia, Omar Fidel; Martino, Anthony A.; Raymer, Michelle; Collins, Aaron M.; Hanson, David T.; Turner, Tom; Powell, Amy Jo; James, Scott Carlton; Timlin, Jerilyn Ann; Scholle, Steven; Dwyer, Brian P.; Ruffing, Anne; Jones, Howland D. T.; Ricken, James Bryce; Reichardt, Thomas A.

    2010-08-01

    The search is on for new renewable energy and algal-derived biofuel is a critical piece in the multi-faceted renewable energy puzzle. It has 30x more oil than any terrestrial oilseed crop, ideal composition for biodiesel, no competition with food crops, can be grown in waste water, and is cleaner than petroleum based fuels. This project discusses these three goals: (1) Conduct fundamental research into the effects that dynamic biotic and abiotic stressors have on algal growth and lipid production - Genomics/Transcriptomics, Bioanalytical spectroscopy/Chemical imaging; (2) Discover spectral signatures for algal health at the benchtop and greenhouse scale - Remote sensing, Bioanalytical spectroscopy; and (3) Develop computational model for algal growth and productivity at the raceway scale - Computational modeling.

  5. Seasonal and altitudinal variations in snow algal communities on an Alaskan glacier (Gulkana glacier in the Alaska range)

    NASA Astrophysics Data System (ADS)

    Takeuchi, Nozomu

    2013-09-01

    Snow and ice algae are cold tolerant algae growing on the surface of snow and ice, and they play an important role in the carbon cycles for glaciers and snowfields in the world. Seasonal and altitudinal variations in seven major taxa of algae (green algae and cyanobacteria) were investigated on the Gulkana glacier in Alaska at six different elevations from May to September in 2001. The snow algal communities and their biomasses changed over time and elevation. Snow algae were rarely observed on the glacier in May although air temperature had been above 0 ° C since the middle of the month and surface snow had melted. In June, algae appeared in the lower areas of the glacier, where the ablation ice surface was exposed. In August, the distribution of algae was extended to the upper parts of the glacier as the snow line was elevated. In September, the glacier surface was finally covered with new winter snow, which terminated algal growth in the season. Mean algal biomass of the study sites continuously increased and reached 6.3 × 10 μl m-2 in cell volume or 13 mg carbon m-2 in September. The algal community was dominated by Chlamydomonas nivalis on the snow surface, and by Ancylonema nordenskiöldii and Mesotaenium berggrenii on the ice surface throughout the melting season. Other algae were less abundant and appeared in only a limited area of the glacier. Results in this study suggest that algae on both snow and ice surfaces significantly contribute to the net production of organic carbon on the glacier and substantially affect surface albedo of the snow and ice during the melting season.

  6. Microbially mediated sulphide production in a thermal, acidic algal mat community in Yellowstone National Park.

    PubMed

    Ferris, Michael J; Magnuson, Timothy S; Fagg, Jennifer A; Thar, Roland; Kühl, Michael; Sheehan, Kathy B; Henson, Joan M

    2003-10-01

    Our objective in this study was to characterize prokaryotic sulphide production within the oxygenic, predominantly eukaryotic algal mat in an acidic stream, Nymph Creek, in Yellowstone National Park (YNP). We used microsensors to examine fluctuations in H2S and O2 concentrations over time through the vertical aspect of the approximately 3 mm mat in a 46-48 degrees C region of the creek. We also used analyses of PCR-amplified 16S rRNA gene sequences obtained from denaturing gradient gels, and PCR-amplified sequences of a functional gene associated with microbial sulphate respiration (dsrA) to characterize the bacterial community in the same region of the mat. During midday, photosynthesis rates were high within the first 500 micro m interval of the mat and high oxygen concentrations (600% air saturation) penetrated deeply (>1800 micro m) into the mat. During early evening and night, oxygen concentrations within the first 1100 micro m of the mat decreased over time from 60% air saturation (a.s) to 12% a.s. A precipitous decline in oxygen concentration occurred at a depth of 1100 micro m in all night measurements and anoxic conditions were present below 1200 micro m. Within this anoxic region, sulphide concentrations increased from nearly 0 micro M at 1200 micro m depth to 100 micro M at 2400 micro m depth. Enrichment cultures inoculated with Nymph Creek mat organisms also produced H2S. Sequence analyses of 16S rRNA and dsrA genes indicated the presence of at least five bacterial genera including species involved in dissimilative sulphate or sulphur reduction. PMID:14510849

  7. Assessment of nutrient enrichment by use of algal-, invertebrate-, and fish-community attributes in wadeable streams in ecoregions surrounding the Great Lakes

    USGS Publications Warehouse

    Frey, Jeffrey W.; Bell, Amanda H.; Hambrook Berkman, Julie A.; Lorenz, David L.

    2011-01-01

    CWPE, algae exhibited greater differences than invertebrates and fish between all of the nutrient categories for both TN and TP; however, in the lower nutrient gradient in the streams of the GNE, invertebrates exhibited greater differences between the nutrient categories. Certain species of algae, invertebrates, and fish were more prevalent in low- and high-nutrient categories within each of the diatom ecoregions. Breakpoint analysis was used to identify the concentration at which the relations between the response variable (biological attribute) and the stressor variable (TN and TP) change. There were significant breakpoints for nutrients (TN and TP) and multiple attributes for algae, invertebrates, and fish communities within the CWPE and GNE diatom ecoregions. In general, more significant breakpoints, with lower concentrations, were found in the GNE than the more nutrient-rich CWPE. The breakpoints from all biological communities were generally about 3-5 times higher in the south (CWPE) than the north (GNE). In the north, breakpoints with similar lower concentrations were found for TN from all biological communities (around 0.60 milligram per liter) and for TP (between 0.02 and 0.03 milligram per liter) for the algae and invertebrate communities. The findings from our study suggest that the range in breakpoints for TN and TP from the GNE can be used as oligotrophic and eutrophic boundaries derived from biological response based on this ecoregion having (1) a gradient with sufficiently low to high nutrient concentrations, (2) distinctive differences in the biological communities in the low- to high-nutrient streams, (3) similarity of breakpoints within algal, invertebrate, and fish communities, (4) significant attributes with either direct relations to nutrients or traditional changes in community structure (that is, decreases in sensitive species or increases in tolerant species), and (5) similar breakpoints in other studies in this and other regions. In nutrie

  8. Algal and fungal diversity in Antarctic lichens.

    PubMed

    Park, Chae Haeng; Kim, Kyung Mo; Elvebakk, Arve; Kim, Ok-Sun; Jeong, Gajin; Hong, Soon Gyu

    2015-01-01

    The composition of lichen ecosystems except mycobiont and photobiont has not been evaluated intensively. In addition, recent studies to identify algal genotypes have raised questions about the specific relationship between mycobiont and photobiont. In the current study, we analyzed algal and fungal community structures in lichen species from King George Island, Antarctica, by pyrosequencing of eukaryotic large subunit (LSU) and algal internal transcribed spacer (ITS) domains of the nuclear rRNA gene. The sequencing results of LSU and ITS regions indicated that each lichen thallus contained diverse algal species. The major algal operational taxonomic unit (OTU) defined at a 99% similarity cutoff of LSU sequences accounted for 78.7-100% of the total algal community in each sample. In several cases, the major OTUs defined by LSU sequences were represented by two closely related OTUs defined by 98% sequence similarity of ITS domain. The results of LSU sequences indicated that lichen-associated fungi belonged to the Arthoniomycetes, Eurotiomycetes, Lecanoromycetes, Leotiomycetes, and Sordariomycetes of the Ascomycota, and Tremellomycetes and Cystobasidiomycetes of the Basidiomycota. The composition of major photobiont species and lichen-associated fungal community were mostly related to the mycobiont species. The contribution of growth forms or substrates on composition of photobiont and lichen-associated fungi was not evident. PMID:25105247

  9. Field and laboratory guide to freshwater cyanobacteria harmful algal blooms for Native American and Alaska Native communities

    USGS Publications Warehouse

    Rosen, Barry H.; Ann St. Amand

    2015-01-01

    Cyanobacteria can produce toxins and form harmful algal blooms. The Native American and Alaska Native communities that are dependent on subsistence fishing have an increased risk of exposure to these cyanotoxins. It is important to recognize the presence of an algal bloom in a waterbody and to distinguish a potentially toxic harmful algal bloom from a non-toxic bloom. This guide provides field images that show cyanobacteria blooms, some of which can be toxin producers, as well as other non-toxic algae blooms and floating plants that might be confused with algae. After recognition of a potential toxin-producing cyanobacterial bloom in the field, the type(s) of cyanobacteria present needs to be identified. Species identification, which requires microscopic examination, may help distinguish a toxin-producer from a non-toxin producer. This guide also provides microscopic images of the common cyanobacteria that are known to produce toxins, as well as images of algae that form blooms but do not produce toxins.

  10. Parasites alter community structure.

    PubMed

    Wood, Chelsea L; Byers, James E; Cottingham, Kathryn L; Altman, Irit; Donahue, Megan J; Blakeslee, April M H

    2007-05-29

    Parasites often play an important role in modifying the physiology and behavior of their hosts and may, consequently, mediate the influence hosts have on other components of an ecological community. Along the northern Atlantic coast of North America, the dominant herbivorous snail Littorina littorea structures rocky intertidal communities through strong grazing pressure and is frequently parasitized by the digenean trematode Cryptocotyle lingua. We hypothesized that the effects of parasitism on host physiology would induce behavioral changes in L. littorea, which in turn would modulate L. littorea's influence on intertidal community composition. Specifically, we hypothesized that C. lingua infection would alter the grazing rate of L. littorea and, consequently, macroalgal communities would develop differently in the presence of infected versus uninfected snails. Our results show that uninfected snails consumed 40% more ephemeral macroalgal biomass than infected snails in the laboratory, probably because the digestive system of infected snails is compromised by C. lingua infection. In the field, this weaker grazing by infected snails resulted in significantly greater expansion of ephemeral macroalgal cover relative to grazing by uninfected snails. By decreasing the per-capita grazing rate of the dominant herbivore, C. lingua indirectly affects the composition of the macroalgal community and may in turn affect other species that depend on macroalgae for resources or habitat structure. In light of the abundance of parasites across systems, we suggest that, through trait-mediated indirect effects, parasites may be a common determinant of structure in ecological communities. PMID:17517667

  11. Development and application of indices to assess the condition of benthic algal communities in U.S. streams and rivers

    USGS Publications Warehouse

    Potapova, Marina; Carlisle, Daren M.

    2011-01-01

    Multi-metric indices (MMIs) are a measure of a combination of characteristics of biological communities and are used as indicators of water quality and ecological health. Although MMIs for algal communities have been developed for specific regions of the United States, none of the indices have national applicability. The MMIs described in this report were developed by the National Water-Quality Assessment Program of the U.S. Geological Survey to assess the overall health of benthic algal communities in U.S. streams and rivers within five geographic regions that encompass the conterminous United States.The traditional procedure for developing MMIs (also referred to as indices of biological integrity) is to select individual metrics that, separately, can distinguish between undisturbed sites (selected for this study as reference sites) and predetermined disturbed sites. The metrics are then combined into a single index. In addition to traditional approaches for selecting individual metrics, the current study used stepwise logistic regressions to select sets of metrics that best predicted whether sites were in an undisturbed or a disturbed condition. Multi-metric indices and logistic regression models were developed for five regions of the United States using calibration datasets and were evaluated using independent validation datasets.

  12. BENTHIC AMPHIPOD COMMUNITY RESPONSE TO STRESS INDUCED BY ALGAL MATS IN A PACIFIC NORTHWEST ESTUARY

    EPA Science Inventory

    Amphipod, algal biomass and sediment samples were taken at two- to four-week intervals from June through December, 2000 along lines perpendicular to two transects in Yaquina Bay, OR, extending from within the Zostera marina bed at the river channel edge through intertidal burrowi...

  13. AMPHIPOD COMMUNITY RESPONSE TO STRESS INDUCED BY ALGAL MATS IN A PACIFIC NORTHWEST ESTUARY

    EPA Science Inventory

    Amphipod, algal and sediment samples were taken at two- to four-week intervals from June through December, 2000 along two transects in Yaquina Bay, OR. The transects extended from within the Zostera marina bed at the river channel edge through intertidal burrowing shrimp ...

  14. Primary production of edaphic algal communities in a Mississippi salt marsh

    SciTech Connect

    Sullivan, M.J.; Moncreiff, C.A.

    1988-03-01

    Primary production rates of edaphic algae associated with the sediments beneath four monospecific canopies of vascular plants were determined over an annual cycle in a Mississippi salt marsh. The edaphic algal flora was dominated by small, motile pennate diatoms. Algal production (as measured by /sup 14/C uptake) was generally highest in spring-early summer and lowest in fall. Hourly rates ranged from a low of 1.4 mg C/m/sup 2/ in Juncus roemerianus Scheele to a high of 163 mg C/m/sup 2/ beneath the Scirpus olneyi Gray canopy. Stepwise multiple regressions identified a soil moisture index and chlorophyll a as the best environmental predictors of hourly production; light energy reaching the marsh surface and sediment and air temperature proved of little value. Adding the relative abundances of 33 diatom taxa to the set of independent variables only slightly increased R/sup 2/; however, virtually all variables selected were diatom taxa. R/sup 2/ was only 0.38 for the Spartina alterniflora Loisel. habitat but ranged from 0.70 to 0.87 for the remaining three vascular plant zones. Annual rates of algal production (g C/m/sup 2/) were estimated as follows: Juncus (28), Spartina (57), Distichlis spicata (L.) Greene (88), and Scirpus (151). The ratio of annual edaphic algal production to vascular plant net aerial production (EAP/VPP) was 10-12% for the first three habitats and 61% for Scirpus. Chlorophyll a concentrations, annual algal production rates, and EAP/VPP values were comparable to those determined in Texas, Delaware, and Massachusetts salt marshes but lower than those reported for Georgia and particularly California marshes.

  15. Algal community characteristics and response to nitrogen and phosphorus concentrations in streams in the Ozark Plateaus, Southern Missouri, 1993-95 and 2006-07

    USGS Publications Warehouse

    Femmer, Suzanne R.

    2012-01-01

    Nutrient and algae data were collected in the 1990s and 2000s by the U.S. Geological Survey for the National Water- Quality Assessment program in the Ozark Highlands, southern Missouri. These data were collected at sites of differing drainage area, land use, nutrient concentrations, and physiography. All samples were collected at sites with a riffle/pool structure and cobble/gravel bed material. A total of 60 samples from 45 sites were available for analyses to determine relations between nutrient concentrations and algal community structure in this region. This information can be used by the Missouri Department of Natural Resources to develop the State's nutrient criteria plan. Water samples collected for this study had total nitrogen concentrations ranging from 0.07 to 4.41 milligram per liter (mg/L) with a median of 0.26 mg/L, and total phosphorus concentrations ranging from 0.003 to 0.78 mg/L with a median of 0.007 mg/L. These nutrient concentrations were transformed into nutrient categories consisting of varying percentiles of data. Algal community data were entered into the U.S. Geological Survey's Algae Data Analysis System for the computation of more than 250 metrics. These metrics were correlated with nutrient categories, and four metrics with the strongest relation with the nutrient data were selected. These metrics were Organic Nitrogen Tolerance, Oxygen Tolerance, Bahls Pollution Class, and the Saprobien index with the 25th and 80th percentile nutrient categories. These data indicate that near the 80th percentile (Total Nitrogen = 0.84 mg/L, Total Phosphorus = 0.035 mg/L) the algae communities significantly changed from nitrogen-fixing species dominance to those species more tolerant of eutrophic conditions.

  16. The relationship between physical variables on topographically simple and complex reefs and algal assemblage structure beneath an Ecklonia radiata canopy

    NASA Astrophysics Data System (ADS)

    Toohey, Benjamin D.

    2007-01-01

    Limestone reefs in South-Western Australia range in topographic complexity at the 1-10 m scale from simple, flat, planar reef structures to topographically complex reefs with many rock walls, overhangs and channels. Algal assemblage structure is known to differ between topographically simple and complex reefs. This research assessed if differences in algal assemblage structure could be associated with the physical environment present on each reef type. Sampling of the physical environment and algal assemblage was carried out on simple, planar reefs and complex, rugose reefs. The physical environment described almost 80% of the algal assemblage structure under an Ecklonia radiata canopy. It was found that topographically simple reefs had greater sediment cover and water depth than adjacent reefs with more complex topography which had more downwelling light, stronger and more turbulent water motion and a greater range of substrate slopes. Greater variation in most physical variables on topographically complex reef shows a greater diversity of microenvironments on that reef type. It is argued that these differences in physical environment between reef types have a considerable influence on algal assemblages by altering key biological processes such as recruitment and interspecific competition.

  17. Change in algal symbiont communities after bleaching, not prior heat exposure, increases heat tolerance of reef corals.

    PubMed

    Silverstein, Rachel N; Cunning, Ross; Baker, Andrew C

    2015-01-01

    Mutualistic organisms can be particularly susceptible to climate change stress, as their survivorship is often limited by the most vulnerable partner. However, symbiotic plasticity can also help organisms in changing environments by expanding their realized niche space. Coral-algal (Symbiodinium spp.) symbiosis exemplifies this dichotomy: the partnership is highly susceptible to 'bleaching' (stress-induced symbiosis breakdown), but stress-tolerant symbionts can also sometimes mitigate bleaching. Here, we investigate the role of diverse and mutable symbiotic partnerships in increasing corals' ability to thrive in high temperature conditions. We conducted repeat bleaching and recovery experiments on the coral Montastraea cavernosa, and used quantitative PCR and chlorophyll fluorometry to assess the structure and function of Symbiodinium communities within coral hosts. During an initial heat exposure (32 °C for 10 days), corals hosting only stress-sensitive symbionts (Symbiodinium C3) bleached, but recovered (at either 24 °C or 29 °C) with predominantly (>90%) stress-tolerant symbionts (Symbiodinium D1a), which were not detected before bleaching (either due to absence or extreme low abundance). When a second heat stress (also 32 °C for 10 days) was applied 3 months later, corals that previously bleached and were now dominated by D1a Symbiodinium experienced less photodamage and symbiont loss compared to control corals that had not been previously bleached, and were therefore still dominated by Symbiodinium C3. Additional corals that were initially bleached without heat by a herbicide (DCMU, at 24 °C) also recovered predominantly with D1a symbionts, and similarly lost fewer symbionts during subsequent thermal stress. Increased thermotolerance was also not observed in C3-dominated corals that were acclimated for 3 months to warmer temperatures (29 °C) before heat stress. These findings indicate that increased thermotolerance post-bleaching resulted from

  18. Distribution of fish, benthic invertebrate, and algal communities in relation to physical and chemical conditions, Yakima River basin, Washington, 1990

    USGS Publications Warehouse

    Cuffney, T.F.; Meador, M.R.; Porter, S.D.; Gurtz, M.E.

    1997-01-01

    Biological investigations were conducted in the Yakima River Basin, Washington, in conjunction with a pilot study for the U.S. Geological Survey's National Water-Quality Assessment Program. Ecological surveys were conducted at 25 sites in 1990 to (1) assess water-quality conditions based on fish, benthic invertebrate, and algal communities; (2) determine the hydrologic, habitat, and chemical factors that affect the distributions of these organisms; and (3) relate physical and chemical conditions to water quality. Results of these investigations showed that land uses and other associated human activities influenced the biological characteristics of streams and rivers and overall water-quality conditions. Fish communities of headwater streams in the Cascades and Eastern Cascades ecoregions of the Yakima River Basin were primarily composed of salmonids and sculpins, with cyprinids dominating in the rest of the basin. The most common of the 33 fish taxa collected were speckled dace, rainbow trout, and Paiute sculpin. The highest number of taxa (193) was found among the inverte- brates. Insects, particularly sensitive forms such as mayflies, stoneflies, and caddisflies (EPT--Ephemeroptera, Plecoptera, and Trichoptera fauna), formed the majority of the invertebrate communities of the Cascades and Eastern Cascades ecoregions. Diatoms dominated algal communities throughout the basin; 134 algal taxa were found on submerged rocks, but other stream microhabitats were not sampled as part of the study. Sensitive red algae and diatoms were predominant in the Cascades and Eastern Cascades ecoregions, whereas the abundance of eutrophic diatoms and green algae was large in the Columbia Basin ecoregion of the Yakima River Basin. Ordination of physical, chemical, and biological site characteristics indicated that elevation was the dominant factor accounting for the distribution of biota in the Yakima River Basin; agricultural intensity and stream size were of secondary importance

  19. Seasonal variation in benthic community oxygen demand: A response to an ice algal bloom in the Beaufort Sea, Canadian Arctic?

    NASA Astrophysics Data System (ADS)

    Renaud, Paul E.; Riedel, Andrea; Michel, Christine; Morata, Nathalie; Gosselin, Michel; Juul-Pedersen, Thomas; Chiuchiolo, Amy

    2007-08-01

    Understanding pathways of carbon cycling on Arctic shelves is critical if we are to evaluate the potential effects of climate change on these systems. We investigated the relationship between ice algal standing stock and benthic respiration between January and July 2004 at a time series station in the southeastern Beaufort Sea. Both ice algal chlorophyll a and benthic sediment oxygen demand showed > 10-fold increases from between March and April. While some of the increase in oxygen demand can be attributed to bacteria and meio-fauna, most was due to the activities of macroinfauna. We also observed a trend toward lower sediment pigment content during the pulse in benthic carbon remineralization. While chl a sedimentation also increased by a factor of 7 during this period, fluxes were not sufficient to provide for the increased carbon demand. We suggest that sedimenting ice algae provided a cue for increased benthic activity, and that direct consumption of ice algae and increased oxygen availability in the sediment due to bioturbation by epifaunal organisms led to the enhancement in respiration rates. Seasonal patterns in primary productivity and the activity of resident epifaunal and infaunal communities are, thus, important factors in determining carbon cycling patterns on Arctic shelves.

  20. Algal Species and Light Microenvironment in a Low-pH, Geothermal Microbial Mat Community

    PubMed Central

    Ferris, M. J.; Sheehan, K. B.; Kühl, M.; Cooksey, K.; Wigglesworth-Cooksey, B.; Harvey, R.; Henson, J. M.

    2005-01-01

    Unicellular algae are the predominant microbial mat-forming phototrophs in the extreme environments of acidic geothermal springs. The ecology of these algae is not well known because concepts of species composition are inferred from cultivated isolates and microscopic observations, methods known to provide incomplete and inaccurate assessments of species in situ. We used sequence analysis of 18S rRNA genes PCR amplified from mat samples from different seasons and different temperatures along a thermal gradient to identify algae in an often-studied acidic (pH 2.7) geothermal creek in Yellowstone National Park. Fiber-optic microprobes were used to show that light for algal photosynthesis is attenuated to <1% over the 1-mm surface interval of the mat. Three algal sequences were detected, and each was present year-round. A Cyanidioschyzon merolae sequence was predominant at temperatures of ≥49°C. A Chlorella protothecoides var. acidicola sequence and a Paradoxia multisita-like sequence were predominant at temperatures of ≤39°C. PMID:16269755

  1. Algal species and light microenvironment in a low-pH, geothermal microbial mat community.

    PubMed

    Ferris, M J; Sheehan, K B; Kühl, M; Cooksey, K; Wigglesworth-Cooksey, B; Harvey, R; Henson, J M

    2005-11-01

    Unicellular algae are the predominant microbial mat-forming phototrophs in the extreme environments of acidic geothermal springs. The ecology of these algae is not well known because concepts of species composition are inferred from cultivated isolates and microscopic observations, methods known to provide incomplete and inaccurate assessments of species in situ. We used sequence analysis of 18S rRNA genes PCR amplified from mat samples from different seasons and different temperatures along a thermal gradient to identify algae in an often-studied acidic (pH 2.7) geothermal creek in Yellowstone National Park. Fiber-optic microprobes were used to show that light for algal photosynthesis is attenuated to < 1% over the 1-mm surface interval of the mat. Three algal sequences were detected, and each was present year-round. A Cyanidioschyzon merolae sequence was predominant at temperatures of > or = 49 degrees C. A Chlorella protothecoides var. acidicola sequence and a Paradoxia multisita-like sequence were predominant at temperatures of < or = 39 degrees C. PMID:16269755

  2. Freshwater benthic algal population and community changes due to acidity and aluminum-acid mixtures in artificial streams

    SciTech Connect

    Genter, R.B.; Amyot, D.J. )

    1994-03-01

    Communities of freshwater benthic algae were exposed to water acidified daily to pH 4.8 along and in mixtures with 50, 100, or 500 [mu]g L[sup [minus]1] Al. Daily acidification to nominal pH 4.8 in acidified treatments exposed algae to a range of pHs that led to a variety of Al species of different toxicity. Calcium concentrations in stream were higher in acidified and Al treatments on day 1, and dissolved Al in stream water was higher in the highest Al treatment on days 1, 7, and 28; otherwise acid and Al treatments did not significantly alter Al and Ca in the exposure water. Calcium bioaccumulation by periphyton was lower in acidified and Al treatments on all sampling days. Concentrations of Mg in water and periphyton did not differ between treatments. The artificial stream system generated alkalinity to buffer acidified water; the amount of generated alkalinity returned to approximately the same levels for the first week, but the amount of alkalinity generated during the second week appeared to decline, and acid-only and acid-Al mixtures diverged in their ability to generate alkalinity during the third and fourth weeks. Aluminum in acidified water inhibited abundance of diatoms and green and blue-green algae more than the effects of acid stress alone. The green filamentous alga Mougeotia showed a slight increase in abundance in the acid-only treatment. The middle-Al treatment generated more alkalinity and had higher abundance of some algal taxa on days 14 and 28, even though measured Al concentrations in water and periphyton fell between low- and high-Al-treatment levels. Community-level tests, combining a taxonomic analysis of algal population abundance with chemical analysis of water and bioaccumulation, provide valuable insight to assess anthropogenic stress.

  3. Distribution, behavior, and condition of herbivorous fishes on coral reefs track algal resources.

    PubMed

    Tootell, Jesse S; Steele, Mark A

    2016-05-01

    Herbivore distribution can impact community structure and ecosystem function. On coral reefs, herbivores are thought to play an important role in promoting coral dominance, but how they are distributed relative to algae is not well known. Here, we evaluated whether the distribution, behavior, and condition of herbivorous fishes correlated with algal resource availability at six sites in the back reef environment of Moorea, French Polynesia. Specifically, we tested the hypotheses that increased algal turf availability would coincide with (1) increased biomass, (2) altered foraging behavior, and (3) increased energy reserves of herbivorous fishes. Fish biomass and algal cover were visually estimated along underwater transects; behavior of herbivorous fishes was quantified by observations of focal individuals; fish were collected to assess their condition; and algal turf production rates were measured on standardized tiles. The best predictor of herbivorous fish biomass was algal turf production, with fish biomass increasing with algal production. Biomass of herbivorous fishes was also negatively related to sea urchin density, suggesting competition for limited resources. Regression models including both algal turf production and urchin density explained 94 % of the variation in herbivorous fish biomass among sites spread over ~20 km. Behavioral observations of the parrotfish Chlorurus sordidus revealed that foraging area increased as algal turf cover decreased. Additionally, energy reserves increased with algal turf production, but declined with herbivorous fish density, implying that algal turf is a limited resource for this species. Our findings support the hypothesis that herbivorous fishes can spatially track algal resources on coral reefs. PMID:26271287

  4. Assessment of potential effects of water produced from coalbed natural gas development on macroinvertebrate and algal communities in the Powder River and Tongue River, Wyoming and Montana, 2010

    USGS Publications Warehouse

    Peterson, David A.; Hargett, Eric G.; Feldman, David L.

    2011-01-01

    Ongoing development of coalbed natural gas in the Powder River structural basin in Wyoming and Montana led to formation of an interagency aquatic task group to address concerns about the effects of the resulting production water on biological communities in streams of the area. Ecological assessments, made from 2005–08 under the direction of the task group, indicated biological condition of the macroinvertebrate and algal communities in the middle reaches of the Powder was lower than in the upper or lower reaches. On the basis of the 2005–08 results, sampling of the macroinvertebrate and algae communities was conducted at 18 sites on the mainstem Powder River and 6 sites on the mainstem Tongue River in 2010. Sampling-site locations were selected on a paired approach, with sites located upstream and downstream of discharge points and tributaries associated with coalbed natural gas development. Differences in biological condition among site pairs were evaluated graphically and statistically using multiple lines of evidence that included macroinvertebrate and algal community metrics (such as taxa richness, relative abundance, functional feeding groups, and tolerance) and output from observed/expected (O/E) macroinvertebrate models from Wyoming and Montana. Multiple lines of evidence indicated a decline in biological condition in the middle reaches of the Powder River, potentially indicating cumulative effects from coalbed natural gas discharges within one or more reaches between Flying E Creek and Wild Horse Creek in Wyoming. The maximum concentrations of alkalinity in the Powder River also occurred in the middle reaches. Biological condition in the upper and lower reaches of the Powder River was variable, with declines between some site pairs, such as upstream and downstream of Dry Fork and Willow Creek, and increases at others, such as upstream and downstream of Beaver Creek. Biological condition at site pairs on the Tongue River showed an increase in one case

  5. Characterization of a Methanogenic Community within an Algal Fed Anaerobic Digester

    PubMed Central

    Ellis, Joshua T.; Tramp, Cody; Sims, Ronald C.; Miller, Charles D.

    2012-01-01

    The microbial diversity and metabolic potential of a methanogenic consortium residing in a 3785-liter anaerobic digester, fed with wastewater algae, was analyzed using 454 pyrosequencing technology. DNA was extracted from anaerobic sludge material and used in metagenomic analysis through PCR amplification of the methyl-coenzyme M reductase α subunit (mcrA) gene using primer sets ML, MCR, and ME. The majority of annotated mcrA sequences were assigned taxonomically to the genera Methanosaeta in the order Methanosarcinales. Methanogens from the genus Methanosaeta are obligate acetotrophs, suggesting this genus plays a dominant role in methane production from the analyzed fermentation sample. Numerous analyzed sequences within the algae fed anaerobic digester were unclassified and could not be assigned taxonomically. Relative amplicon frequencies were determined for each primer set to determine the utility of each in pyrosequencing. Primer sets ML and MCR performed better quantitatively (representing the large majority of analyzed sequences) than primer set ME. However, each of these primer sets was shown to provide a quantitatively unique community structure, and thus they are of equal importance in mcrA metagenomic analysis. PMID:23724331

  6. Biological oxygen demand optode analysis of coral reef-associated microbial communities exposed to algal exudates.

    PubMed

    Gregg, Ak; Hatay, M; Haas, Af; Robinett, Nl; Barott, K; Vermeij, Mja; Marhaver, Kl; Meirelles, P; Thompson, F; Rohwer, F

    2013-01-01

    Algae-derived dissolved organic matter has been hypothesized to induce mortality of reef building corals. One proposed killing mechanism is a zone of hypoxia created by rapidly growing microbes. To investigate this hypothesis, biological oxygen demand (BOD) optodes were used to quantify the change in oxygen concentrations of microbial communities following exposure to exudates generated by turf algae and crustose coralline algae (CCA). BOD optodes were embedded with microbial communities cultured from Montastraea annularis and Mussismilia hispida, and respiration was measured during exposure to turf and CCA exudates. The oxygen concentrations along the optodes were visualized with a low-cost Submersible Oxygen Optode Recorder (SOOpR) system. With this system we observed that exposure to exudates derived from turf algae stimulated higher oxygen drawdown by the coral-associated bacteria than CCA exudates or seawater controls. Furthermore, in both turf and CCA exudate treatments, all microbial communities (coral-, algae-associated and pelagic) contributed significantly to the observed oxygen drawdown. This suggests that the driving factor for elevated oxygen consumption rates is the source of exudates rather than the initially introduced microbial community. Our results demonstrate that exudates from turf algae may contribute to hypoxia-induced coral stress in two different coral genera as a result of increased biological oxygen demand of the local microbial community. Additionally, the SOOpR system developed here can be applied to measure the BOD of any culturable microbe or microbial community. PMID:23882444

  7. Unique picoeukaryotic algal community under multiple environmental stress conditions in a shallow, alkaline pan.

    PubMed

    Pálffy, Károly; Felföldi, Tamás; Mentes, Anikó; Horváth, Hajnalka; Márialigeti, Károly; Boros, Emil; Vörös, Lajos; Somogyi, Boglárka

    2014-01-01

    Winter phytoplankton communities in the shallow alkaline pans of Hungary are frequently dominated by picoeukaryotes, sometimes in particularly high abundance. In winter 2012, the ice-covered alkaline Zab-szék pan was found to be extraordinarily rich in picoeukaryotic green algae (42-82 × 10(6) cells ml(-1)) despite the simultaneous presence of multiple stressors (low temperature and light intensity with high pH and salinity). The maximum photosynthetic rate of the picoeukaryote community was 1.4 μg C μg chlorophyll a (-1) h(-1) at 125 μmol m(-2) s(-1). The assimilation rates compared with the available light intensity measured on the field show that the community was considerably light-limited. Estimated areal primary production was 180 mg C m(-2) d(-1). On the basis of the 18S rRNA gene analysis (cloning and DGGE), the community was phylogenetically heterogeneous with several previously undescribed chlorophyte lineages, which indicates the ability of picoeukaryotic communities to maintain high genetic diversity under extreme conditions. PMID:24281914

  8. Effects of No. 2 Fuel Oil, Nigerian Crude Oil, and Used Crankcase Oil on Attached Algal Communities: Acute and Chronic Toxicity of Water-Soluble Constituents

    PubMed Central

    Bott, Thomas L.; Rogenmuser, Kurt

    1978-01-01

    Water extracts of a no. 2 fuel oil, a Nigerian crude oil, and used crankcase oil were examined for their effects on algal communities in experiments lasting several weeks conducted under near-natural conditions. No. 2 fuel oil extracts depressed algal biomass (chlorophyll a) and resulted in blue-green algal (cyanobacterial) dominance and decreased diatom occurrence. Changes in concentrations of chlorophyll c, which was specific for diatoms in this work, and phycocyanin, which was specific for blue-green algae, confirmed the observations. Used crankcase oil extracts also depressed biomass, but Nigerian crude extracts did not, and both these extracts had less effect on community composition than did no. 2 fuel oil extracts. Photosynthetic 14C incorporation was both stimulated and depressed by exposure to extracts with hydrocarbon concentrations 0.038 to 0.124 mg/liter. Short-term exposure to higher concentrations (1.17 to 15.30 mg of hydrocarbons per liter) of no. 2 fuel oil extracts depressed photosynthetic 14C incorporation by Vaucheria-dominated communities in all tests but one. Toxicity was greater from extracts prepared in the light than from extracts prepared in the dark. PMID:16345329

  9. Effects of no. 2 fuel oil, nigerian crude oil, and used crankcase oil on attached algal communities: acute and chronic toxicity of water-soluble constituents.

    PubMed

    Bott, T L; Rogenmuser, K

    1978-11-01

    Water extracts of a no. 2 fuel oil, a Nigerian crude oil, and used crankcase oil were examined for their effects on algal communities in experiments lasting several weeks conducted under near-natural conditions. No. 2 fuel oil extracts depressed algal biomass (chlorophyll a) and resulted in blue-green algal (cyanobacterial) dominance and decreased diatom occurrence. Changes in concentrations of chlorophyll c, which was specific for diatoms in this work, and phycocyanin, which was specific for blue-green algae, confirmed the observations. Used crankcase oil extracts also depressed biomass, but Nigerian crude extracts did not, and both these extracts had less effect on community composition than did no. 2 fuel oil extracts. Photosynthetic C incorporation was both stimulated and depressed by exposure to extracts with hydrocarbon concentrations 0.038 to 0.124 mg/liter. Short-term exposure to higher concentrations (1.17 to 15.30 mg of hydrocarbons per liter) of no. 2 fuel oil extracts depressed photosynthetic C incorporation by Vaucheria-dominated communities in all tests but one. Toxicity was greater from extracts prepared in the light than from extracts prepared in the dark. PMID:16345329

  10. Characterization of the Kootenai River Algae Community and Primary Productivity Before and After Experimental Nutrient Addition, 2004–2007 [Chapter 2, Kootenai River Algal Community Characterization, 2009 KTOI REPORT].

    SciTech Connect

    Holderman, Charlie; Anders, Paul; Shafii, Bahman

    2009-07-01

    , and a meandering reach. The study design included 14 sampling sites: an upstream, unimpounded reference site (KR-14), four control (non-fertilized) canyon sites downstream from Libby Dam, but upstream from nutrient addition (KR-10 through KR-13), two treatment sites referred to collectively as the nutrient addition zone (KR-9 and KR-9.1, located at and 5 km downstream from the nutrient addition site), two braided reach sites (KR-6 and KR-7), and four meander reach sites (KR-1 through KR-4). A series of qualitative evaluations and quantitative analyses were used to assess baseline conditions and effects of experimental nutrient addition treatments on chlorophyll, primary productivity, and taxonomic composition and metric arrays for the diatom and green algae communities. Insufficient density in the samples precluded analyses of bluegreen algae taxa and metrics for pre- and post-nutrient addition periods. Chlorophyll a concentration (mg/m{sup 2}), chlorophyll accrual rate (mg/m{sup 2}/30d), total chlorophyll concentration (chlorophyll a and b) (mg/m{sup 2}), and total chlorophyll accrual rate (mg/m{sup 2}/30d) were calculated. Algal taxa were identified and grouped by taxonomic order as Cyanophyta (blue-greens), Chlorophyta (greens), Bacillariophyta (diatoms), Chrysophyta (goldens), and dominant species from each sample site were identified. Algal densities (number/ml) in periphyton samples were calculated for each sample site and sampling date. Principal Component Analysis (PCA) was performed to reduce the dimension of diatom and algae data and to determine which taxonomic groups and metrics were contributing significantly to the observed variation. PCA analyses were tabulated to indicate eigenvalues, proportion, and cumulative percent variation, as well as eigenvectors (loadings) for each of the components. Biplot graphic displays of PCA axes were also generated to characterize the pattern and structure of the underlying variation. Taxonomic data and a series of

  11. Benthic plant communities in acidic Lake Colden, New York: Sphagnum and the algal mat

    SciTech Connect

    Hendrey, G R; Vertucci, J A

    1980-03-01

    Lake Colden, in the central Adirondack Mountains of New York State is botanically similar to acidified lakes in Sweden. Acidification of some Swedish lakes has been associated with an expansion of Sphagnum, primarily in shallow, sheltered littoral areas but also to depths of 18m. During a brief botanical survey on 24-25 July 1979, we observed a dense meadow of Sphagnum pylaesii around much of the shoreline of Lake Colden. Plant community composition was determined by a visual estimate of cover along a single typical transect and through underwater photography on 28-29 August 1979. Water samples were collected and returned to our laboratory for analyses several days later. Sample pH was determined by potentiometry and alkalinity by multiple end point titrations. Biomass samples were also taken of the Sphagnum mat community and dry weight was determined. Chemical content of plant tissue was analyzed.

  12. Atrazine does not affect algal biomass or snail populations in microcosm communities at environmentally relevant concentrations.

    PubMed

    Baxter, Leilan R; Moore, Dana L; Sibley, Paul K; Solomon, Keith R; Hanson, Mark L

    2011-07-01

    The herbicide atrazine is a photosynthetic inhibitor used around the world in agricultural applications. Contamination of surface waters adjacent to treated areas can directly reduce growth of nontarget aquatic autotrophs, but the severity of impacts is highly dependent on species sensitivity and exposure concentration. Secondary effects resulting from macrophyte or phytoplankton decline may include an expansion of the more tolerant periphyton community. Recently, this shift in the autotrophic community has been proposed as a mechanism for increased rates of parasite infections in amphibians via augmented populations of aquatic snails which act as intermediate hosts to larval trematodes. To further clarify this relationship, an outdoor microcosm study was conducted to examine the effects of atrazine on primary production and snail populations over a range of environmentally relevant concentrations. In July 2009, 15 experimental ponds were treated to achieve initial concentrations of 0, 1, 10, 30, and 100 µg/L atrazine. Over a period of 73 d, measures were taken of macrophyte, phytoplankton, and periphyton biomass, growth, and fecundity of caged snails (Physella spp. and Stagnicola elodes) and free-living snails (Physella spp.). Except for declines in macrophyte biomass at the highest treatment level, no consistent relationships were found between atrazine concentration and any measured parameter. Comparison of these results with previous findings highlights the variability of responses to atrazine exposure between similarly constructed freshwater communities, even at concentrations up to 20 times higher than sustained environmental levels. PMID:21567448

  13. Quantitative structure-activity relationships (QSARs) using the novel marine algal toxicity data of phenols.

    PubMed

    Ertürk, M Doğa; Saçan, Melek Türker; Novic, Marjana; Minovski, Nikola

    2012-09-01

    The present study reports for the first time in its entirety the toxicity of 30 phenolic compounds to marine alga Dunaliella tertiolecta. Toxicity of polar narcotics and respiratory uncouplers was strongly correlated to hydrophobicity as described by the logarithm of the octanol/water partition coefficient (Log P). Compounds expected to act by more reactive mechanisms, particularly hydroquinones, were shown to have toxicity in excess of that predicted by Log P. A quality quantitative structure-activity relationship (QSAR) was obtained with Log P and a 2D autocorrelation descriptor weighted by atomic polarizability (MATS3p) only after the removal of hydroquinones from the data set. In an attempt to model the whole data set including hydroquinones, 3D descriptors were included in the modeling process and three quality QSARs were developed using multiple linear regression (MLR). One of the most significant results of the present study was the superior performance of the consensus MLR model, obtained by averaging the predictions from each individual linear model, which provided excellent prediction accuracy for the test set (Q(test)²=0.94). The four-parameter Counter Propagation Artificial Neural Network (CP ANN) model, which was constructed using four out of six descriptors that appeared in the linear models, also provided an excellent external predictivity (Q(test)²=0.93). The proposed algal QSARs were further tested in their predictivity using an external set comprising toxicity data of 44 chemicals on freshwater alga Pseudokirchneriella subcapitata. The two-parameter global model employing a 3D descriptor (Mor24m) and a charge-related descriptor (C(ortho)) not only had high external predictivity (Q(ext)²=0.74), but it also had excellent external data set coverage (%97). PMID:23085159

  14. Voluntary Associations and Community Structure.

    ERIC Educational Resources Information Center

    Dillman, Don A.; And Others

    This study examined overlapping membership of voluntary associations as the basis of a statistical technique for analyzing community structure. An underlying assumption was that organizations select certain membership linkages in preference to others within a community. Thus one would expect to find points of integration and cleavage among…

  15. Coralline algal structure is more sensitive to rate, rather than the magnitude, of ocean acidification

    PubMed Central

    Kamenos, Nicholas A; Burdett, Heidi L; Aloisio, Elena; Findlay, Helen S; Martin, Sophie; Longbone, Charlotte; Dunn, Jonathan; Widdicombe, Stephen; Calosi, Piero

    2013-01-01

    Marine pCO2 enrichment via ocean acidification (OA), upwelling and release from carbon capture and storage (CCS) facilities is projected to have devastating impacts on marine biomineralisers and the services they provide. However, empirical studies using stable endpoint pCO2 concentrations find species exhibit variable biological and geochemical responses rather than the expected negative patterns. In addition, the carbonate chemistry of many marine systems is now being observed to be more variable than previously thought. To underpin more robust projections of future OA impacts on marine biomineralisers and their role in ecosystem service provision, we investigate coralline algal responses to realistically variable scenarios of marine pCO2 enrichment. Coralline algae are important in ecosystem function; providing habitats and nursery areas, hosting high biodiversity, stabilizing reef structures and contributing to the carbon cycle. Red coralline marine algae were exposed for 80 days to one of three pH treatments: (i) current pH (control); (ii) low pH (7.7) representing OA change; and (iii) an abrupt drop to low pH (7.7) representing the higher rates of pH change observed at natural vent systems, in areas of upwelling and during CCS releases. We demonstrate that red coralline algae respond differently to the rate and the magnitude of pH change induced by pCO2 enrichment. At low pH, coralline algae survived by increasing their calcification rates. However, when the change to low pH occurred at a fast rate we detected, using Raman spectroscopy, weaknesses in the calcite skeleton, with evidence of dissolution and molecular positional disorder. This suggests that, while coralline algae will continue to calcify, they may be structurally weakened, putting at risk the ecosystem services they provide. Notwithstanding evolutionary adaptation, the ability of coralline algae to cope with OA may thus be determined primarily by the rate, rather than magnitude, at which pCO2

  16. Effects of intracellular structural associations on degradation of algal chloropigments in natural oxic and anoxic seawaters

    NASA Astrophysics Data System (ADS)

    Ding, Haibing; Sun, Ming-Yi

    2005-09-01

    To understand the effects of intracellular structural associations on degradation of algal chloropigments, we conducted a series of microcosm experiments by incubating Emiliania huxleyi cells (a marine haptophyte) in natural oxic and anoxic seawaters collected from a stratified water column in the Cariaco Basin. The incubated cell detritus were sequentially treated with two buffer solutions to separate pigment components into soluble and insoluble fractions. By using non-denaturing gel electrophoresis, several chlorophyll-complexes, free chlorophyll, and another unknown chlorophyll-containing component were further separated from the soluble fraction. The chlorophyll-complexes included those bound with high molecular weight core-proteins (CP-I and CP43+CP47) and low molecular weight polypeptides (LHC-I and LHC-II) in the cellular photosystems PS-I and PS-II. Overall pigment recovery from these fractions and gel bands was well equivalent to the total amount from direct acetone extraction of the cells. We followed the time-dependent concentration changes of chlorophyll-a (Chl-a), phaeophorbide-a (Ppb-a), and phaeophytin-a (Ppt-a) in all fractions and complexes to estimate the degradation rate constants of chloropigments in natural oxic and anoxic seawaters. Our experimental results demonstrated that the intracellular structural associations had important influences on degradation of chloropigments under different redox conditions. In general, total Chl-a degraded faster (˜4X) in oxic seawater than in anoxic seawater. However, the rate differences between oxic and anoxic conditions varied among the fractions and complexes. Degradation rate constants of Chl-a in soluble fraction were much higher (>10X) than those in insoluble fraction under both oxic and anoxic conditions. Chl-a bound with the complexes in PS-II appeared to be more reactive (˜2X) than that in PS-I under oxic conditions but the difference in degradation rate constants between two photosystems became

  17. Seasonal synchronicity of algal assemblages in three Midwestern agricultural streams having varying concentrations of atrazine, nutrients, and sediment.

    PubMed

    Andrus, J Malia; Winter, Diane; Scanlan, Michael; Sullivan, Sean; Bollman, Wease; Waggoner, J B; Hosmer, Alan J; Brain, Richard A

    2013-08-01

    Numerous studies characterizing the potential effects of atrazine on algal assemblages have been conducted using micro- or mesocosms; however, few evaluations focused on in situ lotic algal communities, potentially confounding risk assessment conclusions. This exploratory study, conducted at several sites in the midwestern United States where atrazine is commonly used, presents in situ observations of native algal communities relative to atrazine exposure and other parameters. Planktonic and periphytic algae from three streams in three Midwestern states, having historically differing atrazine levels, were sampled over a 16-week period in 2011 encompassing atrazine applications and the summer algal growth period at each site. Changes in abundance, diversity, and composition of algal communities were placed in the context of hydrological, climatic, and water quality parameters (including components sometimes present in agricultural runoff) also collected during the study. Diatoms dominated communities at each of the three sites and periphyton was much more abundant than phytoplankton. As expected, significant variations in algal community and environmental parameters were observed between sites. However, correspondence analysis plots revealed that patterns of temporal variation in algal communities at each site and in periphyton or phytoplankton were dominated by seasonal environmental gradients. Significant concordance in these seasonal patterns was detected among sites and between phytoplankton and periphyton communities (via procrustes Protest analysis), suggesting synchronicity of algal communities across a regional scale. While atrazine concentrations generally exhibited seasonal trends at the study watersheds; no effects on algal abundance, diversity or assemblage structure were observed as a result of atrazine pulses. This lack of response may be due to exposure events of insufficient concentration or duration (consistent with previously reported results) or

  18. Cost structures and life cycle impacts of algal biomass and biofuel production

    NASA Astrophysics Data System (ADS)

    Christiansen, Katrina Lea

    2011-12-01

    Development and extraction of energy sources, energy production and energy use have huge economic, environmental and geopolitical impacts. Increasing energy demands in tandem with reductions in fossil fuel production has led to significant investments in research into alternative forms of energy. One that is promising but yet not commercially established is the production of biofuel from algae. This research quantitatively assessed the potential of algae biofuel production by examining its cost and environmental impacts. First, two models developed by the RAND corporation were employed to assess Cost Growth defined as the ratio of actual costs to estimated costs, and Plant Performance defined as the ratio of actual production levels to design performance, of three algal biofuel production technologies. The three algal biofuel production technologies examined to open raceway ponds (ORPs), photobioreactors (PBRs), and a system that couples PBRs to ORPs (PBR-ORPs). Though these analyses lack precision due to uncertainty, the results highlight the risks associated with implementing algal biofuel systems, as all scenarios examined were predicted to have Cost Growth, ranging from 1.2 to 1.8, and Plant Performance was projected as less than 50% of design performance for all cases. Second, the Framework the Evaluation of Biomass Energy Feedstocks (FEBEF) was used to assess the cost and environmental impacts of biodiesel produced from three algal production technologies. When these results were compared with ethanol from corn and biodiesel from soybeans, biodiesel from algae produced from the different technologies were estimated to be more expensive, suffered from low energy gains, and did not result in lower greenhouse gas emissions. To identify likely routes to making algal biofuels more competitive, a third study was undertaken. In this case, FEBEF was employed to examine pinch-points (defined as the most costly, energy consuming, greenhouse gas producing processes), in

  19. Interactive effects of ocean acidification and warming on coral reef associated epilithic algal communities under past, present-day and future ocean conditions

    NASA Astrophysics Data System (ADS)

    Vogel, N.; Cantin, N. E.; Strahl, J.; Kaniewska, P.; Bay, L.; Wild, C.; Uthicke, S.

    2016-06-01

    Epilithic algal communities play critical ecological roles on coral reefs, but their response to individual and interactive effects of ocean warming (OW) and ocean acidification (OA) is still largely unknown. We investigated growth, photosynthesis and calcification of early epilithic algal community assemblages exposed for 6 months to four temperature profiles (-1.1, ±0.0, +0.9, +1.6 °C) that were crossed with four carbon dioxide partial pressure (pCO2) levels (360, 440, 650, 940 µatm), under flow-through conditions and natural light regimes. Additionally, we compared the cover of heavily calcified crustose coralline algae (CCA) and lightly calcified red algae of the genus Peyssonnelia among treatments. Increase in cover of epilithic communities showed optima under moderately elevated temperatures and present pCO2, while cover strongly decreased under high temperatures and high-pCO2 conditions, particularly due to decreasing cover of CCA. Similarly, community calcification rates were strongly decreased at high pCO2 under both measured temperatures. While final cover of CCA decreased under high temperature and pCO2 (additive negative effects), cover of Peyssonnelia spp. increased at high compared to annual average and moderately elevated temperatures. Thus, cover of Peyssonnelia spp. increased in treatment combinations with less CCA, which was supported by a significant negative correlation between organism groups. The different susceptibility to stressors most likely derived from a different calcification intensity and/or mineral. Notably, growth of the epilithic communities and final cover of CCA were strongly decreased under reduced-pCO2 conditions compared to the present. Thus, CCA may have acclimatized from past to present-day pCO2 conditions, and changes in carbonate chemistry, regardless in which direction, negatively affect them. However, if epilithic organisms cannot further acclimatize to OW and OA, the interacting effects of both factors may change

  20. Molecular evidence for a diverse green algal community growing in the hair of sloths and a specific association with Trichophilus welckeri (Chlorophyta, Ulvophyceae)

    PubMed Central

    2010-01-01

    Background Sloths are slow-moving arboreal mammals inhabiting tropical rainforests in Central and South America. The six living species of sloths are occasionally reported to display a greenish discoloration of their pelage. Trichophilus welckeri, a green algal species first described more than a century ago, is widely believed to discolor the animals fur and provide the sloth with effective camouflage. However, this phenomenon has not been explored in any detail and there is little evidence to substantiate this widely held opinion. Results Here we investigate the genetic diversity of the eukaryotic community present in fur of all six extant species of sloth. Analysis of 71 sloth hair samples yielding 426 partial 18S rRNA gene sequences demonstrates a diverse eukaryotic microbial assemblage. Phylogenetic analysis reveals that sloth fur hosts a number of green algal species and suggests that acquisition of these organisms from the surrounding rainforest plays an important role in the discoloration of sloth fur. However, an alga corresponding to the morphological description of Trichophilus welckeri was found to be frequent and abundant on sloth fur. Phylogenetic analysis demonstrated the retention of this alga on the fur of sloths independent of geographic location. Conclusions These results demonstrate a unique diverse microbial eukaryotic community in the fur of sloths from Central and South America. Our analysis streghtens the case for symbiosis between sloths and Trichophilus welckeri. PMID:20353556

  1. Algicidal bacteria in the sea and their impact on algal blooms.

    PubMed

    Mayali, Xavier; Azam, Farooq

    2004-01-01

    Over the past two decades, many reports have revealed the existence of bacteria capable of killing phytoplankton. These algicidal bacteria sometimes increase in abundance concurrently with the decline of algal blooms, suggesting that they may affect algal bloom dynamics. Here, we synthesize the existing knowledge on algicidal bacteria interactions with marine eukaryotic microalgae. We discuss the effectiveness of the current methods to characterize the algicidal phenotype in an ecosystem context. We briefly consider the literature on the phylogenetic identification of algicidal bacteria, their interaction with their algal prey, the characterization of algicidal molecules, and the enumeration of algicidal bacteria during algal blooms. We conclude that, due to limitations of current methods, the evidence for algicidal bacteria causing algal bloom decline is circumstantial. New methods and an ecosystem approach are needed to test hypotheses on the impact of algicidal bacteria in algal bloom dynamics. This will require enlarging the scope of inquiry from its current focus on the potential utility of algicidal bacteria in the control of harmful algal blooms. We suggest conceptualizing bacterial algicidy within the general problem of bacterial regulation of algal community structure in the ocean. PMID:15134248

  2. A trait based dynamic energy budget approach to explore emergent microalgal community structure

    NASA Astrophysics Data System (ADS)

    Cheng, Y.; Bouskill, N.; Karaoz, U.; Geng, H.; Lane, T.; Pett-Ridge, J.; Mayali, X.; Brodie, E.

    2015-12-01

    Microalgae play important roles in the global carbon budget. Phytoplankton, including microalgae, are responsible for around 50% of global primary production, and also hold promise as a viable renewable biofuel source. Research has been underway for decades to realize the full potential of algal biofuels at the commercial scale, however, uni-algal ponds are typically threatened by collapse due to microalgal grazing and parasite invasions. Recently, it has been proposed that functionally diverse microalgal-bacterial communities can achieve high biomass and/or lipid yields, and are more stable (less susceptible to invasion) than a monoculture. Similar positive diversity-productivity relationships have been observed in a wide range of ecosystem studies, but the purposeful maintenance of a diverse microbiome is less common in managed systems. In our work, a trait based dynamic energy budget model was developed to explore emergent microalgal community structure under various environmental (e.g. light, temperature, nutrient availability) conditions. The complex algal community can be reduced into functional groups (guilds). Each guild (algae or bacteria) is characterized by distinct physiological traits (e.g. nutrient requirement, growth rate, substrate affinity, lipid production) constrained by biochemical trade-offs. These trait values are derived from literature and information encoded in genomic data. Metabolism of the algae and the bacterial species (symbiotic or non-symbiotic) are described within a dynamic energy budget framework. The model offers a mechanistic framework to predict the optimal microalgal community assemblage towards high productivity and resistance to invasion under prevailing environmental conditions.

  3. Detection of community structure in networks based on community coefficients

    NASA Astrophysics Data System (ADS)

    Lu, Hu; Wei, Hui

    2012-12-01

    Determining community structure in networks is fundamental to the analysis of the structural and functional properties of those networks, including social networks, computer networks, and biological networks. Modularity function Q, which was proposed by Newman and Girvan, was once the most widely used criterion for evaluating the partition of a network into communities. However, modularity Q is subject to a serious resolution limit. In this paper, we propose a new function for evaluating the partition of a network into communities. This is called community coefficient C. Using community coefficient C, we can automatically identify the ideal number of communities in the network, without any prior knowledge. We demonstrate that community coefficient C is superior to the modularity Q and does not have a resolution limit. We also compared the two widely used community structure partitioning methods, the hierarchical partitioning algorithm and the normalized cuts (Ncut) spectral partitioning algorithm. We tested these methods on computer-generated networks and real-world networks whose community structures were already known. The Ncut algorithm and community coefficient C were found to produce better results than hierarchical algorithms. Unlike several other community detection methods, the proposed method effectively partitioned the networks into different community structures and indicated the correct number of communities.

  4. Algal functional annotation tool

    2012-07-12

    Abstract BACKGROUND: Progress in genome sequencing is proceeding at an exponential pace, and several new algal genomes are becoming available every year. One of the challenges facing the community is the association of protein sequences encoded in the genomes with biological function. While most genome assembly projects generate annotations for predicted protein sequences, they are usually limited and integrate functional terms from a limited number of databases. Another challenge is the use of annotations tomore » interpret large lists of 'interesting' genes generated by genome-scale datasets. Previously, these gene lists had to be analyzed across several independent biological databases, often on a gene-by-gene basis. In contrast, several annotation databases, such as DAVID, integrate data from multiple functional databases and reveal underlying biological themes of large gene lists. While several such databases have been constructed for animals, none is currently available for the study of algae. Due to renewed interest in algae as potential sources of biofuels and the emergence of multiple algal genome sequences, a significant need has arisen for such a database to process the growing compendiums of algal genomic data. DESCRIPTION: The Algal Functional Annotation Tool is a web-based comprehensive analysis suite integrating annotation data from several pathway, ontology, and protein family databases. The current version provides annotation for the model alga Chlamydomonas reinhardtii, and in the future will include additional genomes. The site allows users to interpret large gene lists by identifying associated functional terms, and their enrichment. Additionally, expression data for several experimental conditions were compiled and analyzed to provide an expression-based enrichment search. A tool to search for functionally-related genes based on gene expression across these conditions is also provided. Other features include dynamic visualization of genes on

  5. Algal functional annotation tool

    SciTech Connect

    2012-07-12

    Abstract BACKGROUND: Progress in genome sequencing is proceeding at an exponential pace, and several new algal genomes are becoming available every year. One of the challenges facing the community is the association of protein sequences encoded in the genomes with biological function. While most genome assembly projects generate annotations for predicted protein sequences, they are usually limited and integrate functional terms from a limited number of databases. Another challenge is the use of annotations to interpret large lists of 'interesting' genes generated by genome-scale datasets. Previously, these gene lists had to be analyzed across several independent biological databases, often on a gene-by-gene basis. In contrast, several annotation databases, such as DAVID, integrate data from multiple functional databases and reveal underlying biological themes of large gene lists. While several such databases have been constructed for animals, none is currently available for the study of algae. Due to renewed interest in algae as potential sources of biofuels and the emergence of multiple algal genome sequences, a significant need has arisen for such a database to process the growing compendiums of algal genomic data. DESCRIPTION: The Algal Functional Annotation Tool is a web-based comprehensive analysis suite integrating annotation data from several pathway, ontology, and protein family databases. The current version provides annotation for the model alga Chlamydomonas reinhardtii, and in the future will include additional genomes. The site allows users to interpret large gene lists by identifying associated functional terms, and their enrichment. Additionally, expression data for several experimental conditions were compiled and analyzed to provide an expression-based enrichment search. A tool to search for functionally-related genes based on gene expression across these conditions is also provided. Other features include dynamic visualization of genes on KEGG

  6. Production and stability of structured lipids from algal oils and capric acid.

    PubMed

    Hamam, Fayez; Shahidi, Fereidoon

    2004-01-01

    This study aimed to incorporate capric acid (CA) into selected algal oils, namely arachidoinc acid single cell oil (ARASCO), docosahexaenoic acid single cell oil (DHASCO) and the OMEGA-GOLD oil rich in dcosahexaenoic acid (DHA) and dosapentaenoic acid (n-6 DPA). Response surface methodology indicated that under optimum conditions (12.3% enzyme, 45 degrees C, and 29.4 h) CA incorporation was 20.0% into ARASCO; (4.2% enzyme, 43.3 degrees C, and 27.1 h) 22.6% into DHASCO and (2.5% enzyme, 46.6 degrees C and 25.2 h) 20.7% into the OMEGA-GOLD oil. Stereospecific analysis indicated that in all oils examined CA was mainly located at the sn-1 and sn-3 positions of the resultant TAG molecules while the highly unsaturated fatty acids being primarily esterified to the sn-2 positions of the three oils. In all cases, enzymatically modified oils were more susceptible to oxidation than their unmodified counterparts. PMID:15630303

  7. Discovering Network Structure Beyond Communities

    PubMed Central

    Nishikawa, Takashi; Motter, Adilson E.

    2011-01-01

    To understand the formation, evolution, and function of complex systems, it is crucial to understand the internal organization of their interaction networks. Partly due to the impossibility of visualizing large complex networks, resolving network structure remains a challenging problem. Here we overcome this difficulty by combining the visual pattern recognition ability of humans with the high processing speed of computers to develop an exploratory method for discovering groups of nodes characterized by common network properties, including but not limited to communities of densely connected nodes. Without any prior information about the nature of the groups, the method simultaneously identifies the number of groups, the group assignment, and the properties that define these groups. The results of applying our method to real networks suggest the possibility that most group structures lurk undiscovered in the fast-growing inventory of social, biological, and technological networks of scientific interest. PMID:22355667

  8. Effects of fish density and river fertilization on algal standing stocks, invertebrates communities, and fish production in an Arctic River

    USGS Publications Warehouse

    Deegan, Linda A.; Peterson, B.J.; Golden, H.; McIvor, C.C.; Miller, M.C.

    1997-01-01

    This study examined the relative importance of bottom-up and top-down controls of an arctic stream food web by simultaneous manipulation of the top predator and nutrient availability. We created a two-step trophic system (algae to insects) by removal of the top predator (Arctic grayling, Thymallus arcticus) in fertilized and control stream reaches. Fish abundance was also increased 10 times to examine the effect of high fish density on stream ecosystem dynamics and fish. We measured the response of epilithic algae, benthic and drifting insects, and fish to nutrient enrichment and to changes in fish density. Insect grazers had little effect on algae and fish had little effect on insects. In both the control and fertilized reaches, fish growth, energy storage, and reproductive response of females declined with increased fish density. Fish growth and energy storage were more closely correlated with per capita insect availability than with per capita algal standing stock

  9. Microbial-algal community changes during the latest Permian ecological crisis: Evidence from lipid biomarkers at Cili, South China

    NASA Astrophysics Data System (ADS)

    Luo, Genming; Wang, Yongbiao; Grice, Kliti; Kershaw, Steve; Algeo, Thomas J.; Ruan, Xiaoyan; Yang, Hao; Jia, Chengling; Xie, Shucheng

    2013-06-01

    Microbialites flourished globally immediately following the latest Permian mass extinction. In this study, lipid biomarker records were analyzed in the Cili section (Hunan Province, South China) in order to determine the types of microbes involved in microbialite formation and their response to contemporaneous environmental changes. Various biomarkers were identified in the aliphatic and aromatic fractions using gas chromatography (GC) and GC-mass spectrometry (GC-MS). Low abundance of steranes in the microbialite layer suggests that it did not contain large amounts of algae, in striking contrast to the abundant algal fossils and algal-derived steranes present in the underlying (pre-crisis) skeletal limestone. Although pristine/phytane (Pr/Ph) ratios increased in the microbialite layer, covariation of Pr/Ph with the ratio of low- to high-molecular-weight n-alkanes (C20 -/C20 +) suggests that the former proxy was controlled by microbial (particularly cyanobacterial) inputs rather than by redox conditions. The microbialite also yielded low ratios of hopanes to short-chain n-alkanes (HP/Lalk) and high abundances of C21n-alkylcyclohexane, indicating that, in addition to cyanobacteria, anaerobic bacteria, archaea, and possibly acritarchs flourished in the aftermath of the marine extinction event. The upper part of the thinly bedded micritic limestone overlying the microbialite exhibits a bimodal distribution of n-alkanes as well as increased abundances of extended tricyclic terpanes and steranes, suggesting a return of habitable shallow-marine conditions for eukaryotic algae several hundred thousand years after the latest Permian mass extinction. Increases in the dibenzofuran ratio (i.e., DBF/(DBF + DBT + F)) and in the coronene to phenanthrene ratio (Cor/P) in the skeletal limestone immediately below the microbialite are evidence of enhanced soil erosion rates and wildfire intensity, marking the collapse of terrestrial ecosystems. The terrestrial crisis thus slightly

  10. Significant Scales in Community Structure

    PubMed Central

    Traag, V. A.; Krings, G.; Van Dooren, P.

    2013-01-01

    Many complex networks show signs of modular structure, uncovered by community detection. Although many methods succeed in revealing various partitions, it remains difficult to detect at what scale some partition is significant. This problem shows foremost in multi-resolution methods. We here introduce an efficient method for scanning for resolutions in one such method. Additionally, we introduce the notion of “significance” of a partition, based on subgraph probabilities. Significance is independent of the exact method used, so could also be applied in other methods, and can be interpreted as the gain in encoding a graph by making use of a partition. Using significance, we can determine “good” resolution parameters, which we demonstrate on benchmark networks. Moreover, optimizing significance itself also shows excellent performance. We demonstrate our method on voting data from the European Parliament. Our analysis suggests the European Parliament has become increasingly ideologically divided and that nationality plays no role. PMID:24121597

  11. Response of algal metrics to nutrients and physical factors and identification of nutrient thresholds in agricultural streams

    USGS Publications Warehouse

    Black, R.W.; Moran, P.W.; Frankforter, J.D.

    2011-01-01

    Many streams within the United States are impaired due to nutrient enrichment, particularly in agricultural settings. The present study examines the response of benthic algal communities in agricultural and minimally disturbed sites from across the western United States to a suite of environmental factors, including nutrients, collected at multiple scales. The first objective was to identify the relative importance of nutrients, habitat and watershed features, and macroinvertebrate trophic structure to explain algal metrics derived from deposition and erosion habitats. The second objective was to determine if thresholds in total nitrogen (TN) and total phosphorus (TP) related to algal metrics could be identified and how these thresholds varied across metrics and habitats. Nutrient concentrations within the agricultural areas were elevated and greater than published threshold values. All algal metrics examined responded to nutrients as hypothesized. Although nutrients typically were the most important variables in explaining the variation in each of the algal metrics, environmental factors operating at multiple scales also were important. Calculated thresholds for TN or TP based on the algal metrics generated from samples collected from erosion and deposition habitats were not significantly different. Little variability in threshold values for each metric for TN and TP was observed. The consistency of the threshold values measured across multiple metrics and habitats suggest that the thresholds identified in this study are ecologically relevant. Additional work to characterize the relationship between algal metrics, physical and chemical features, and nuisance algal growth would be of benefit to the development of nutrient thresholds and criteria. ?? 2010 The Author(s).

  12. Response of algal metrics to nutrients and physical factors and identification of nutrient thresholds in agricultural streams.

    PubMed

    Black, Robert W; Moran, Patrick W; Frankforter, Jill D

    2011-04-01

    Many streams within the United States are impaired due to nutrient enrichment, particularly in agricultural settings. The present study examines the response of benthic algal communities in agricultural and minimally disturbed sites from across the western United States to a suite of environmental factors, including nutrients, collected at multiple scales. The first objective was to identify the relative importance of nutrients, habitat and watershed features, and macroinvertebrate trophic structure to explain algal metrics derived from deposition and erosion habitats. The second objective was to determine if thresholds in total nitrogen (TN) and total phosphorus (TP) related to algal metrics could be identified and how these thresholds varied across metrics and habitats. Nutrient concentrations within the agricultural areas were elevated and greater than published threshold values. All algal metrics examined responded to nutrients as hypothesized. Although nutrients typically were the most important variables in explaining the variation in each of the algal metrics, environmental factors operating at multiple scales also were important. Calculated thresholds for TN or TP based on the algal metrics generated from samples collected from erosion and deposition habitats were not significantly different. Little variability in threshold values for each metric for TN and TP was observed. The consistency of the threshold values measured across multiple metrics and habitats suggest that the thresholds identified in this study are ecologically relevant. Additional work to characterize the relationship between algal metrics, physical and chemical features, and nuisance algal growth would be of benefit to the development of nutrient thresholds and criteria. PMID:20577796

  13. Tracing the early development of harmful algal blooms on the West Florida Shelf with the aid of Lagrangian coherent structures

    NASA Astrophysics Data System (ADS)

    Olascoaga, M. J.; Beron-Vera, F. J.; Brand, L. E.; KoçAk, H.

    2008-12-01

    Several theories have been proposed to explain the development of harmful algal blooms (HABs) produced by the toxic dinoflagellate Karenia brevis on the West Florida Shelf. However, because the early stages of HAB development are usually not detected, these theories have been so far very difficult to verify. In this paper we employ simulated Lagrangian coherent structures (LCSs) to trace potential early locations of the development of a HAB in late 2004 before it was transported to a region where it could be detected by satellite imagery. The LCSs, which are extracted from surface ocean currents produced by a data-assimilative HYCOM (HYbrid-Coordinate Ocean Model) simulation, constitute material fluid barriers that demarcate potential pathways for HAB evolution. Using a simplified population dynamics model we infer the factors that could possibly lead to the development of the HAB in question. The population dynamics model determines nitrogen in two components, nutrients and phytoplankton, which are assumed to be passively advected by surface ocean currents produced by the above HYCOM simulation. Two nutrient sources are inferred for the HAB whose evolution is found to be strongly tied to the simulated LCSs. These nutrient sources are found to be located nearshore and possibly due to land runoff.

  14. Algal bioassessment metrics for wadeable streams and rivers of Maine, USA

    USGS Publications Warehouse

    Danielson, T.J.; Loftin, C.S.; Tsomides, L.; Difranco, J.L.; Connors, B.

    2011-01-01

    Many state water-quality agencies use biological assessment methods based on lotic fish and macroinvertebrate communities, but relatively few states have incorporated algal multimetric indices into monitoring programs. Algae are good indicators for monitoring water quality because they are sensitive to many environmental stressors. We evaluated benthic algal community attributes along a landuse gradient affecting wadeable streams and rivers in Maine, USA, to identify potential bioassessment metrics. We collected epilithic algal samples from 193 locations across the state. We computed weighted-average optima for common taxa for total P, total N, specific conductance, % impervious cover, and % developed watershed, which included all land use that is no longer forest or wetland. We assigned Maine stream tolerance values and categories (sensitive, intermediate, tolerant) to taxa based on their optima and responses to watershed disturbance. We evaluated performance of algal community metrics used in multimetric indices from other regions and novel metrics based on Maine data. Metrics specific to Maine data, such as the relative richness of species characterized as being sensitive in Maine, were more correlated with % developed watershed than most metrics used in other regions. Few community-structure attributes (e.g., species richness) were useful metrics in Maine. Performance of algal bioassessment models would be improved if metrics were evaluated with attributes of local data before inclusion in multimetric indices or statistical models. ?? 2011 by The North American Benthological Society.

  15. Green algal infection of American horseshoe crab (Limulus polyphemus) exoskeletal structures.

    PubMed

    Braverman, Hillary; Leibovitz, Louis; Lewbart, Gregory A

    2012-09-15

    Degenerative lesions in the dorsum of the horseshoe crab (Limulus polyphemus) exoskeleton, eyes, arthrodial membrane, and base of the telson were documented in a population of wild caught laboratory animals. The disease can lead to loss of tissue structure and function, deformed shells, abnormal molting, loss of ocular structures, erosion of interskeletal membranes, and cardiac hemorrhage. Microscopy, histopathology, and in vitro culture confirmed the causative agent to be a green algae of the family Ulvaceae. Further research may explain how green algae overcome horseshoe crab innate immunity leading to external and internal damage. PMID:22709543

  16. Lagrangian Coherent Structures (LCS) and the dispersion of algal bloom and marine debris in the Yellow and East China Sea

    NASA Astrophysics Data System (ADS)

    Kim, Y. H.; Choi, B.; Son, Y. B.; Shim, W. J.; Hwang, J. H.; Park, Y.

    2012-12-01

    Series of satellite images show that the development and migration of green macroalgal bloom (known as Ulva prolifera) in the Yellow Sea (YS) and Eastern China Sea (ECS). This presentation will utilize the Lagrangian Coherent Structures (LCS) analysis to demonstrate the dispersion pattern of algal bloom patches. Analyzing LCS such as stable and unstable manifolds is one of emerging technologies for characterizing Lagrangian pathways in aquatic environments. This approach is based on the assumption that unstable manifolds such as ridges (i.e., high values) in the finite-time Lyapunov exponent (FTLE) fields coincide with material transport barriers. In this study, the FTLE fields were computed from gridded trajectories using flow fields provided by Regional Ocean Modeling System (ROMS) in the YS/ECS during summer 2011. The results show that there exist two strong transport barriers that lie along the east-west direction, at least, for the simulation period; one is located from the north of Changjiang River mouth to the middle of the Yellow Sea and the other one is stretched from the south of Shandong Peninsular toward east/southeast. This LCS analysis suggests that patches of green algae developed in the coastal region of Jiangsu Province during summer may migrate toward east into the middle of the YS or even toward Korean coast rather than extending along the Jiangsu coast, which is consistent with the observation results derived from the satellite ocean color data. In the very same manner, the utilization of LCS results to evaluate the distribution/transport pattern of marine debris in the YS/ECS will also be discussed during the presentation.

  17. Internal structure of segment reefs: Halimeda algal mounds in the Mediterranean Miocene

    NASA Astrophysics Data System (ADS)

    Braga, Juan C.; Martín, José M.; Riding, Robert

    1996-01-01

    Halimeda reefs in the upper Miocene strata (˜6 Ma) of the Sorbas basin, southeastern Spain, shed light on the internal structure of more extensive but less accessible Holocene counterparts, and challenge conventional reef concepts. Coarse discoid segments, released by Halimeda during life or immediately after death, dominate the lenslike mounds. Their chaotic, loose appearance disguises the reefal nature of the mounds. Segments, accumulating at or very close to sites of growth, were quickly stabilized by microbial and cement crusts that bound them into distinctive rigid gravel fabrics. This early lithification generated relief but inhibited off-mound export of sediment, although large blocks detached locally and moved downslope. Encrustation of parautochthonous Halimeda gravel created a unique reef type: segment reefs.

  18. Simple probabilistic algorithm for detecting community structure

    NASA Astrophysics Data System (ADS)

    Ren, Wei; Yan, Guiying; Liao, Xiaoping; Xiao, Lan

    2009-03-01

    With the growing number of available social and biological networks, the problem of detecting the network community structure is becoming more and more important which acts as the first step to analyze these data. The community structure is generally regarded as that nodes in the same community tend to have more edges and less if they are in different communities. We propose a simple probabilistic algorithm for detecting community structure which employs expectation-maximization (SPAEM). We also give a criterion based on the minimum description length to identify the optimal number of communities. SPAEM can detect overlapping nodes and handle weighted networks. It turns out to be powerful and effective by testing simulation data and some widely known data sets.

  19. Community Structure in Directed Networks

    NASA Astrophysics Data System (ADS)

    Leicht, E. A.; Newman, M. E. J.

    2008-03-01

    We consider the problem of finding communities or modules in directed networks. In the past, the most common approach to this problem has been to ignore edge direction and apply methods developed for community discovery in undirected networks, but this approach discards potentially useful information contained in the edge directions. Here we show how the widely used community finding technique of modularity maximization can be generalized in a principled fashion to incorporate information contained in edge directions. We describe an explicit algorithm based on spectral optimization of the modularity and show that it gives demonstrably better results than previous methods on a variety of test networks, both real and computer generated.

  20. Community structure in the phonological network

    PubMed Central

    Siew, Cynthia S. Q.

    2013-01-01

    Community structure, which refers to the presence of densely connected groups within a larger network, is a common feature of several real-world networks from a variety of domains such as the human brain, social networks of hunter-gatherers and business organizations, and the World Wide Web (Porter et al., 2009). Using a community detection technique known as the Louvain optimization method, 17 communities were extracted from the giant component of the phonological network described in Vitevitch (2008). Additional analyses comparing the lexical and phonological characteristics of words in these communities against words in randomly generated communities revealed several novel discoveries. Larger communities tend to consist of short, frequent words of high degree and low age of acquisition ratings, and smaller communities tend to consist of longer, less frequent words of low degree and high age of acquisition ratings. Real communities also contained fewer different phonological segments compared to random communities, although the number of occurrences of phonological segments found in real communities was much higher than that of the same phonological segments in random communities. Interestingly, the observation that relatively few biphones occur very frequently and a large number of biphones occur rarely within communities mirrors the pattern of the overall frequency of words in a language (Zipf, 1935). The present findings have important implications for understanding the dynamics of activation spread among words in the phonological network that are relevant to lexical processing, as well as understanding the mechanisms that underlie language acquisition and the evolution of language. PMID:23986735

  1. Social significance of community structure: Statistical view

    NASA Astrophysics Data System (ADS)

    Li, Hui-Jia; Daniels, Jasmine J.

    2015-01-01

    Community structure analysis is a powerful tool for social networks that can simplify their topological and functional analysis considerably. However, since community detection methods have random factors and real social networks obtained from complex systems always contain error edges, evaluating the significance of a partitioned community structure is an urgent and important question. In this paper, integrating the specific characteristics of real society, we present a framework to analyze the significance of a social community. The dynamics of social interactions are modeled by identifying social leaders and corresponding hierarchical structures. Instead of a direct comparison with the average outcome of a random model, we compute the similarity of a given node with the leader by the number of common neighbors. To determine the membership vector, an efficient community detection algorithm is proposed based on the position of the nodes and their corresponding leaders. Then, using a log-likelihood score, the tightness of the community can be derived. Based on the distribution of community tightness, we establish a connection between p -value theory and network analysis, and then we obtain a significance measure of statistical form . Finally, the framework is applied to both benchmark networks and real social networks. Experimental results show that our work can be used in many fields, such as determining the optimal number of communities, analyzing the social significance of a given community, comparing the performance among various algorithms, etc.

  2. Social significance of community structure: statistical view.

    PubMed

    Li, Hui-Jia; Daniels, Jasmine J

    2015-01-01

    Community structure analysis is a powerful tool for social networks that can simplify their topological and functional analysis considerably. However, since community detection methods have random factors and real social networks obtained from complex systems always contain error edges, evaluating the significance of a partitioned community structure is an urgent and important question. In this paper, integrating the specific characteristics of real society, we present a framework to analyze the significance of a social community. The dynamics of social interactions are modeled by identifying social leaders and corresponding hierarchical structures. Instead of a direct comparison with the average outcome of a random model, we compute the similarity of a given node with the leader by the number of common neighbors. To determine the membership vector, an efficient community detection algorithm is proposed based on the position of the nodes and their corresponding leaders. Then, using a log-likelihood score, the tightness of the community can be derived. Based on the distribution of community tightness, we establish a connection between p-value theory and network analysis, and then we obtain a significance measure of statistical form . Finally, the framework is applied to both benchmark networks and real social networks. Experimental results show that our work can be used in many fields, such as determining the optimal number of communities, analyzing the social significance of a given community, comparing the performance among various algorithms, etc. PMID:25679651

  3. RANGELAND COMMUNITIES: STRUCTURE, FUNCTION, AND CLASSIFICATION

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Determining the vegetational attributes of rangelands is critical to their management. Yet incorporating vegetation structure, function, and classification into a single chapter is an ambitious goal and an attempt to blur the boundaries between classical community ecology that characterize patterns...

  4. Photophysiology and albedo-changing potential of the ice algal community on the surface of the Greenland ice sheet.

    PubMed

    Yallop, Marian L; Anesio, Alexandre M; Perkins, Rupert G; Cook, Joseph; Telling, Jon; Fagan, Daniel; MacFarlane, James; Stibal, Marek; Barker, Gary; Bellas, Chris; Hodson, Andy; Tranter, Martyn; Wadham, Jemma; Roberts, Nicholas W

    2012-12-01

    Darkening of parts of the Greenland ice sheet surface during the summer months leads to reduced albedo and increased melting. Here we show that heavily pigmented, actively photosynthesising microalgae and cyanobacteria are present on the bare ice. We demonstrate the widespread abundance of green algae in the Zygnematophyceae on the ice sheet surface in Southwest Greenland. Photophysiological measurements (variable chlorophyll fluorescence) indicate that the ice algae likely use screening mechanisms to downregulate photosynthesis when exposed to high intensities of visible and ultraviolet radiation, rather than non-photochemical quenching or cell movement. Using imaging microspectrophotometry, we demonstrate that intact cells and filaments absorb light with characteristic spectral profiles across ultraviolet and visible wavelengths, whereas inorganic dust particles typical for these areas display little absorption. Our results indicate that the phototrophic community growing directly on the bare ice, through their photophysiology, most likely have an important role in changing albedo, and subsequently may impact melt rates on the ice sheet. PMID:23018772

  5. Photophysiology and albedo-changing potential of the ice algal community on the surface of the Greenland ice sheet

    PubMed Central

    Yallop, Marian L; Anesio, Alexandre M; Perkins, Rupert G; Cook, Joseph; Telling, Jon; Fagan, Daniel; MacFarlane, James; Stibal, Marek; Barker, Gary; Bellas, Chris; Hodson, Andy; Tranter, Martyn; Wadham, Jemma; Roberts, Nicholas W

    2012-01-01

    Darkening of parts of the Greenland ice sheet surface during the summer months leads to reduced albedo and increased melting. Here we show that heavily pigmented, actively photosynthesising microalgae and cyanobacteria are present on the bare ice. We demonstrate the widespread abundance of green algae in the Zygnematophyceae on the ice sheet surface in Southwest Greenland. Photophysiological measurements (variable chlorophyll fluorescence) indicate that the ice algae likely use screening mechanisms to downregulate photosynthesis when exposed to high intensities of visible and ultraviolet radiation, rather than non-photochemical quenching or cell movement. Using imaging microspectrophotometry, we demonstrate that intact cells and filaments absorb light with characteristic spectral profiles across ultraviolet and visible wavelengths, whereas inorganic dust particles typical for these areas display little absorption. Our results indicate that the phototrophic community growing directly on the bare ice, through their photophysiology, most likely have an important role in changing albedo, and subsequently may impact melt rates on the ice sheet. PMID:23018772

  6. Arctic spring awakening - Steering principles behind the phenology of vernal ice algal blooms

    NASA Astrophysics Data System (ADS)

    Leu, E.; Mundy, C. J.; Assmy, P.; Campbell, K.; Gabrielsen, T. M.; Gosselin, M.; Juul-Pedersen, T.; Gradinger, R.

    2015-12-01

    Marine ecosystems at high latitudes are characterized by extreme seasonal changes in light conditions, as well as a limited period of high primary production during spring and early summer. As light returns at the end of winter to Arctic ice-covered seas, a first algal bloom takes place in the bottom layer of the sea ice. This bottom ice algae community develops through three distinct phases in the transition from winter to spring, starting with phase I, a predominantly net heterotroph community that has limited interaction with the pelagic or benthic realms. Phase II begins in the spring once light for photosynthesis becomes available at the ice bottom, although interaction with the water column and benthos remains limited. The transition to the final phase III is then mainly driven by a balance of atmospheric and oceanographic forcing that induce structural changes in the sea ice and ultimately the removal of algal biomass from the ice. Due to limited data availability an incomplete understanding exists of all the processes determining ice algal bloom phenology and the considerable geographic differences in sympagic algal standing stocks and primary production. We present here the first pan-Arctic compilation of available time-series data on vernal sea ice algal bloom development and identify the most important factors controlling its development and termination. Using data from the area surrounding Resolute Bay (Nunavut, Canada) as an example, we support previous investigations that snow cover on top of the ice influences sea ice algal phenology, with highest biomass development, but also earliest termination of blooms, under low snow cover. We also provide a pan-Arctic overview of sea ice algae standing stocks and primary production, and discuss the pertinent processes behind the geographic differences we observed. Finally, we assess potential future changes in vernal algal bloom phenology as a consequence of climate change, including their importance to

  7. Changes in the Structure of the Microbial Community Associated with Nannochloropsis salina following Treatments with Antibiotics and Bioactive Compounds

    DOE PAGESBeta

    Geng, Haifeng; Tran-Gyamfi, Mary B.; Lane, Todd W.; Sale, Kenneth L.; Yu, Eizadora T.

    2016-07-26

    Open microalgae cultures host a myriad of bacteria, creating a complex system of interacting species that influence algal growth and health. Many algal microbiota studies have been conducted to determine the relative importance of bacterial taxa to algal culture health and physiological states, but these studies have not characterized the interspecies relationships in the microbial communities. Here we subjected Nanochroloropsis salina cultures to multiple chemical treatments (antibiotics and quorum sensing compounds) and obtained dense time-series data on changes to the microbial community using 16S gene amplicon metagenomic sequencing (21,029,577 reads for 23 samples) to measure microbial taxa-taxa abundance correlations. Short-termmore » treatment with antibiotics resulted in substantially larger shifts in the microbiota structure compared to changes observed following treatment with signaling compounds and glucose. We also calculated operational taxonomic unit (OTU) associations and generated OTU correlation networks to provide an overview of possible bacterial OTU interactions. This analysis identified five major cohesive modules of microbiota with similar co-abundance profiles across different chemical treatments. The Eigengenes of OTU modules were examined for correlation with different external treatment factors. This correlation-based analysis revealed that culture age (time) and treatment types have primary effects on forming network modules and shaping the community structure. Additional network analysis detected Alteromonadeles and Alphaproteobacteria as having the highest centrality, suggesting these species are “keystone” OTUs in the microbial community. Furthermore, we illustrated that the chemical tropodithietic acid, which is secreted by several species in the Alphaproteobacteria taxon, is able to drastically change the structure of the microbiota within 3 h. Lastly, taken together, these results provide valuable insights into the structure

  8. Changes in the Structure of the Microbial Community Associated with Nannochloropsis salina following Treatments with Antibiotics and Bioactive Compounds.

    PubMed

    Geng, Haifeng; Tran-Gyamfi, Mary B; Lane, Todd W; Sale, Kenneth L; Yu, Eizadora T

    2016-01-01

    Open microalgae cultures host a myriad of bacteria, creating a complex system of interacting species that influence algal growth and health. Many algal microbiota studies have been conducted to determine the relative importance of bacterial taxa to algal culture health and physiological states, but these studies have not characterized the interspecies relationships in the microbial communities. We subjected Nanochroloropsis salina cultures to multiple chemical treatments (antibiotics and quorum sensing compounds) and obtained dense time-series data on changes to the microbial community using 16S gene amplicon metagenomic sequencing (21,029,577 reads for 23 samples) to measure microbial taxa-taxa abundance correlations. Short-term treatment with antibiotics resulted in substantially larger shifts in the microbiota structure compared to changes observed following treatment with signaling compounds and glucose. We also calculated operational taxonomic unit (OTU) associations and generated OTU correlation networks to provide an overview of possible bacterial OTU interactions. This analysis identified five major cohesive modules of microbiota with similar co-abundance profiles across different chemical treatments. The Eigengenes of OTU modules were examined for correlation with different external treatment factors. This correlation-based analysis revealed that culture age (time) and treatment types have primary effects on forming network modules and shaping the community structure. Additional network analysis detected Alteromonadeles and Alphaproteobacteria as having the highest centrality, suggesting these species are "keystone" OTUs in the microbial community. Furthermore, we illustrated that the chemical tropodithietic acid, which is secreted by several species in the Alphaproteobacteria taxon, is able to drastically change the structure of the microbiota within 3 h. Taken together, these results provide valuable insights into the structure of the microbiota

  9. Changes in the Structure of the Microbial Community Associated with Nannochloropsis salina following Treatments with Antibiotics and Bioactive Compounds

    PubMed Central

    Geng, Haifeng; Tran-Gyamfi, Mary B.; Lane, Todd W.; Sale, Kenneth L.; Yu, Eizadora T.

    2016-01-01

    Open microalgae cultures host a myriad of bacteria, creating a complex system of interacting species that influence algal growth and health. Many algal microbiota studies have been conducted to determine the relative importance of bacterial taxa to algal culture health and physiological states, but these studies have not characterized the interspecies relationships in the microbial communities. We subjected Nanochroloropsis salina cultures to multiple chemical treatments (antibiotics and quorum sensing compounds) and obtained dense time-series data on changes to the microbial community using 16S gene amplicon metagenomic sequencing (21,029,577 reads for 23 samples) to measure microbial taxa-taxa abundance correlations. Short-term treatment with antibiotics resulted in substantially larger shifts in the microbiota structure compared to changes observed following treatment with signaling compounds and glucose. We also calculated operational taxonomic unit (OTU) associations and generated OTU correlation networks to provide an overview of possible bacterial OTU interactions. This analysis identified five major cohesive modules of microbiota with similar co-abundance profiles across different chemical treatments. The Eigengenes of OTU modules were examined for correlation with different external treatment factors. This correlation-based analysis revealed that culture age (time) and treatment types have primary effects on forming network modules and shaping the community structure. Additional network analysis detected Alteromonadeles and Alphaproteobacteria as having the highest centrality, suggesting these species are “keystone” OTUs in the microbial community. Furthermore, we illustrated that the chemical tropodithietic acid, which is secreted by several species in the Alphaproteobacteria taxon, is able to drastically change the structure of the microbiota within 3 h. Taken together, these results provide valuable insights into the structure of the microbiota

  10. Deciphering Network Community Structure by Surprise

    PubMed Central

    Aldecoa, Rodrigo; Marín, Ignacio

    2011-01-01

    The analysis of complex networks permeates all sciences, from biology to sociology. A fundamental, unsolved problem is how to characterize the community structure of a network. Here, using both standard and novel benchmarks, we show that maximization of a simple global parameter, which we call Surprise (S), leads to a very efficient characterization of the community structure of complex synthetic networks. Particularly, S qualitatively outperforms the most commonly used criterion to define communities, Newman and Girvan's modularity (Q). Applying S maximization to real networks often provides natural, well-supported partitions, but also sometimes counterintuitive solutions that expose the limitations of our previous knowledge. These results indicate that it is possible to define an effective global criterion for community structure and open new routes for the understanding of complex networks. PMID:21909420

  11. Methods for collecting algal samples as part of the National Water-Quality Assessment Program

    USGS Publications Warehouse

    Porter, Stephen D.; Cuffney, Thomas F.; Gurtz, Martin E.; Meador, Michael R.

    1993-01-01

    Benthic algae (periphyton) and phytoplankton communities are characterized in the U.S. Geological Survey's National Water-Quality Assessment Program as part of an integrated physical, chemical, and biological assessment of the Nation's water quality. This multidisciplinary approach provides multiple lines of evidence for evaluating water-quality status and trends, and for refining an understanding of the factors that affect water-quality conditions locally, regionally, and nationally. Water quality can be characterized by evaluating the results of qualitative and quantitative measurements of the algal community. Qualitative periphyton samples are collected to develop of list of taxa present in the sampling reach. Quantitative periphyton samples are collected to measure algal community structure within selected habitats. These samples of benthic algal communities are collected from natural substrates, using the sampling methods that are most appropriate for the habitat conditions. Phytoplankton samples may be collected in large nonwadeable streams and rivers to meet specific program objectives. Estimates of algal biomass (chlorophyll content and ash-free dry mass) also are optional measures that may be useful for interpreting water-quality conditions. A nationally consistent approach provides guidance on site, reach, and habitat selection, as well as information on methods and equipment for qualitative and quantitative sampling. Appropriate quality-assurance and quality-control guidelines are used to maximize the ability to analyze data locally, regionally, and nationally.

  12. Resilience and recovery: the effect of triclosan exposure timing during development, on the structure and function of river biofilm communities.

    PubMed

    Lawrence, J R; Topp, E; Waiser, M J; Tumber, V; Roy, J; Swerhone, G D W; Leavitt, P; Paule, A; Korber, D R

    2015-04-01

    Triclosan (TCS) is a ubiquitous antibacterial agent found in soaps, scrubs, and consumer products. There is limited information on hazardous effects of TCS in the environment. Here, rotating annular reactors were used to cultivate river biofilm communities exposed to 1.8 μg l(-1) TCS with the timing and duration of exposure and recovery during development varied. Two major treatment regimens were employed: (i) biofilm development for 2, 4 or 6 weeks prior to TCS exposure and (ii) exposure of biofilms to TCS for 2, 4 or 6 weeks followed by recovery. Biofilms not exposed to TCS were used as a reference condition. Communities cultivated without and then exposed to TCS all exhibited reductions in algal biomass and significant (p<0.05) reductions in cyanobacterial biomass. No significant effects were observed on bacterial biomass. CLSM imaging of biofilms at 8 weeks revealed unique endpoints in terms of community architecture. Community composition was altered by any exposure to TCS, as indicated by significant shifts in denaturing gradient gel electrophoresis fingerprints and exopolymer composition relative to the reference. Bacterial, algal and cyanobacterial components initially exposed to TCS were significantly different from those TCS-free at time zero. Pigment analyses suggested that significant changes in composition of algal and cyanobacterial populations occurred with TCS exposure. Bacterial thymidine incorporation rates were reduced by TCS exposure and carbon utilization spectra shifted in terms substrate metabolism. Direct counts of protozoans indicated that TCS was suppressive, whereas micrometazoan populations were, in some instances, stimulated. These results indicate that even a relatively brief exposure of a river biofilm community to relatively low levels of TCS alters both the trajectory and final community structure. Although some evidence of recovery was observed, removal of TCS did not result in a return to the unexposed reference condition. PMID

  13. Centrality measures for networks with community structure

    NASA Astrophysics Data System (ADS)

    Gupta, Naveen; Singh, Anurag; Cherifi, Hocine

    2016-06-01

    Understanding the network structure, and finding out the influential nodes is a challenging issue in large networks. Identifying the most influential nodes in a network can be useful in many applications like immunization of nodes in case of epidemic spreading, during intentional attacks on complex networks. A lot of research is being done to devise centrality measures which could efficiently identify the most influential nodes in a network. There are two major approaches to this problem: On one hand, deterministic strategies that exploit knowledge about the overall network topology, while on the other end, random strategies are completely agnostic about the network structure. Centrality measures that can deal with a limited knowledge of the network structure are of prime importance. Indeed, in practice, information about the global structure of the overall network is rarely available or hard to acquire. Even if available, the structure of the network might be too large that it is too much computationally expensive to calculate global centrality measures. To that end, a centrality measure is proposed here that requires information only at the community level. Indeed, most of the real-world networks exhibit a community structure that can be exploited efficiently to discover the influential nodes. We performed a comparative evaluation of prominent global deterministic strategies together with stochastic strategies, an available and the proposed deterministic community-based strategy. Effectiveness of the proposed method is evaluated by performing experiments on synthetic and real-world networks with community structure in the case of immunization of nodes for epidemic control.

  14. Environmental Regulation of Microbial Community Structure

    NASA Technical Reports Server (NTRS)

    Bebout, Leslie; DesMarais, D.; Heyenga, G.; Nelson, F.; DeVincenzi, D. (Technical Monitor)

    2002-01-01

    Most naturally occurring microbes live in complex microbial communities consisting of thousands of phylotypes of microorganisms living in close proximity. Each of these draws nutrients from the environment and releases metabolic waste products, which may in turn serve as substrates for other microbial groups. Gross environmental changes, such as irradiance level, hydrodynamic flow regime, temperature or water chemistry can directly affect the productivity of some community members, which in turn will affect other dependent microbial populations and rate processes. As a first step towards the development of "standard" natural communities of microorganisms for a variety of potential NASA applications, we are measuring biogeochemical cycling in artificially structured communities of microorganisms, created using natural microbial mat communities as inoculum. The responses of these artificially assembled communities of microorganisms to controlled shifts in ecosystem incubation conditions is being determined. This research requires close linking of environmental monitoring, with community composition in a closed and controlled incubation setting. We are developing new incubation chamber designs to allow for this integrated approach to examine the interplay between environmental conditions, microbial community composition and biogeochemical processes.

  15. COMPARISON OF LARGE RIVER SAMPLING METHODS ON ALGAL METRICS

    EPA Science Inventory

    We compared the results of four methods used to assess the algal communities at 60 sites distributed among four rivers. Based on Principle Component Analysis of physical habitat data collected concomitantly with the algal data, sites were separated into those with a mean thalweg...

  16. Impact of phytoplankton community structure and function on marine particulate optical properties

    NASA Astrophysics Data System (ADS)

    McFarland, Malcolm Neil

    Phytoplankton are an ecologically important and diverse group of organisms whose distribution, abundance, and population dynamics vary significantly over small spatial (cm) and temporal (minutes) scales in the coastal ocean. Our inability to observe phytoplankton community structure and function at these small scales has severely limited our understanding of the fundamental ecological and evolutionary mechanisms that drive phytoplankton growth, mortality, adaptation and speciation. The goal of this dissertation was to enhance our understanding of phytoplankton ecology by improving in situ observational techniques based on the optical properties of cells, colonies, populations, and communities. Field and laboratory studies were used to determine the effects of phytoplankton species composition, morphology, and physiology on the inherent optical properties of communities and to explore the adaptive significance of bio-optically important cellular characteristics. Initial field studies found a strong association between species composition and the relative magnitude and shape of particulate absorption, scattering, and attenuation coefficient spectra. Subsequent field studies using scanning flow cytometry to directly measure optically important phytoplankton and non-algal particle characteristics demonstrated that the size and pigment content of large (>20 microm) phytoplankton cells and colonies vary significantly with the slope of particulate attenuation and absorption spectra, and with the ratio of particulate scattering to absorption. These relationships enabled visualization of phytoplankton community composition and mortality over small spatial and temporal scales derived from high resolution optical measurements acquired with an autonomous profiling system. Laboratory studies with diverse uni-algal cultures showed that morphological and physiological characteristics of cells and colonies can account for ˜30% of the optical variation observed in natural

  17. Integrating macroecological metrics and community taxonomic structure.

    PubMed

    Harte, John; Rominger, Andrew; Zhang, Wenyu

    2015-10-01

    We extend macroecological theory based on the maximum entropy principle from species level to higher taxonomic categories, thereby predicting distributions of species richness across genera or families and the dependence of abundance and metabolic rate distributions on taxonomic tree structure. Predictions agree with qualitative trends reported in studies on hyper-dominance in tropical tree species, mammalian body size distributions and patterns of rarity in worldwide plant communities. Predicted distributions of species richness over genera or families for birds, arthropods, plants and microorganisms are in excellent agreement with data. Data from an intertidal invertebrate community, but not from a dispersal-limited forest, are in excellent agreement with a predicted new relationship between body size and abundance. Successful predictions of the original species level theory are unmodified in the extended theory. By integrating macroecology and taxonomic tree structure, maximum entropy may point the way towards a unified framework for understanding phylogenetic community structure. PMID:26248954

  18. Closed benchmarks for network community structure characterization

    NASA Astrophysics Data System (ADS)

    Aldecoa, Rodrigo; Marín, Ignacio

    2012-02-01

    Characterizing the community structure of complex networks is a key challenge in many scientific fields. Very diverse algorithms and methods have been proposed to this end, many working reasonably well in specific situations. However, no consensus has emerged on which of these methods is the best to use in practice. In part, this is due to the fact that testing their performance requires the generation of a comprehensive, standard set of synthetic benchmarks, a goal not yet fully achieved. Here, we present a type of benchmark that we call “closed,” in which an initial network of known community structure is progressively converted into a second network whose communities are also known. This approach differs from all previously published ones, in which networks evolve toward randomness. The use of this type of benchmark allows us to monitor the transformation of the community structure of a network. Moreover, we can predict the optimal behavior of the variation of information, a measure of the quality of the partitions obtained, at any moment of the process. This enables us in many cases to determine the best partition among those suggested by different algorithms. Also, since any network can be used as a starting point, extensive studies and comparisons can be performed using a heterogeneous set of structures, including random ones. These properties make our benchmarks a general standard for comparing community detection algorithms.

  19. Structural Impacts on Thallus and Algal Cell Components of Two Lichen Species in Response to Low-Level Air Pollution in Pacific Northwest Forests

    NASA Astrophysics Data System (ADS)

    Ra, Hyung-Shim Y.; Rubin, Laura; Crang, Richard F. E.

    2004-04-01

    Lichens have long been regarded as bioindicators of air pollution, and structural studies typically have indicated negative impacts in highly polluted areas. In this research, Parmelia sulcata and Platismatia glauca were collected from one clean and two polluted sites in the Pacific Northwest forests of the United States to investigate the anatomical and ultrastructural responses of relatively resistant lichens to moderate air pollution. Light microscopy of polluted materials revealed only slight increases in the algal cell proportions of the thallus, and a decrease in the fungal cells of the medulla. Using transmission electron microscopy, increased lipid droplets in the cytoplasm and an increase in the cell wall thickness of the photobionts were found in the polluted lichens. These results were compared with physiological data in which the net carbon uptake did not show any significant differences; however, the total chlorophyll content was heightened in the polluted samples. The increased total chlorophyll content and the absence of any changes in the algal cell proportions of the polluted samples suggest that the photobionts possessed a higher chlorophyll content per unit volume of the photobiont at polluted sites. The results also indicate that lichens have altered their storage allocation in different cellular compartments. This may be a result of symbiotic readjustment(s) between the photobiont and the mycobiont. In comparison with the physiological results from these two species, these changes do not represent damaging effects by low-level air pollution.

  20. Cross-habitat interactions among bivalve species control community structure on intertidal flats.

    PubMed

    Donadi, Serena; van der Heide, Tjisse; van der Zee, Els M; Eklöf, Johan S; van de Koppel, Johan; Weerman, Ellen J; Piersma, Theunis; Olff, Han; Eriksson, Britas Klemens

    2013-02-01

    Increasing evidence shows that spatial interactions between sedentary organisms can structure communities and promote landscape complexity in many ecosystems. Here we tested the hypothesis that reef-forming mussels (Mytilus edulis L.), a dominant intertidal ecosystem engineer in the Wadden Sea, promote abundances of the burrowing bivalve Cerastoderma edule L. (cockle) in neighboring habitats at relatively long distances coastward from mussel beds. Field surveys within and around three mussel beds showed a peak in cockle densities at 50-100 m toward the coast from the mussel bed, while cockle abundances elsewhere in the study area were very low. Field transplantation of cockles showed higher survival of young cockles (2-3 years old) and increased spat fall coastward of the mussel bed compared to within the bed and to areas without mussels, whereas growth decreased within and coastward of the mussel bed. Our measurements suggest that the observed spatial patterns in cockle numbers resulted from (1) inhibition effects by the mussels close to the beds due to preemptive algal depletion and deteriorated sediment conditions and (2) facilitation effects by the mussels farther away from the beds due to reduction of wave energy. Our results imply that these spatial, scale-dependent interactions between reef-forming ecosystem engineers and surrounding communities of sedentary benthic organisms can be an important determinant of the large-scale community structure in intertidal ecosystems. Understanding this interplay between neighboring communities of sedentary species is therefore essential for effective conservation and restoration of soft-bottom intertidal communities. PMID:23691667

  1. Direct Effect of Carbon Dioxide Concentration on Phytoplankton Community Structure in the Ross Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    Riesselman, C. R.; Tortell, P. D.; Payne, C. D.; Dunbar, R. B.; Ditullio, G. R.

    2006-12-01

    As the largest high-nutrient low-chlorophyll (HNLC) region on the planet, the Southern Ocean plays a critical role in global biogeochemical cycling and climate modulation. Primary productivity and phytoplankton community structure in the waters surrounding Antarctica have demonstrated unique sensitivity to small changes in major and trace element availability and vertical mixing. However, the capacity of changing atmospheric CO2 to restructure Antarctic phytoplankton communities has only recently been proposed. During the austral summer of 2005-2006, the "Controls on Ross Sea Algal Community Structure" (CORSACS) project performed an integrated series of shipboard incubations coupled with polynya water column sampling designed to investigate the interplay of iron, light, and CO2 levels as determinants of primary production and phytoplankton community structure. Results from the CORSACS CO2 manipulation incubation experiment demonstrate substantial shifts in the taxonomic distribution of phytoplankton exposed to an experimental CO2 gradient. Triplicate semi-continuous culture bottles were bubbled with air mixtures containing 100, 370, and 800 ppm CO2, designed to approximate bloom conditions under glacial, modern, and projected future levels of carbon dioxide. At the conclusion of the 18-day incubation, the 100 ppm community was dominated by the small, finely silicified pennate diatom Pseudonitzschia subcurvata, while the abundance of larger, colonial Chaetoceros species increased significantly in the 800 ppm community. These results represent the first evidence that perturbations in atmospheric CO2 have the potential to reorganize phytoplankton community structure in the Southern Ocean, and have implications for both the glacial productivity paradox and the future of polar trophic structure.

  2. Eukaryotic algal phytochromes span the visible spectrum.

    PubMed

    Rockwell, Nathan C; Duanmu, Deqiang; Martin, Shelley S; Bachy, Charles; Price, Dana C; Bhattacharya, Debashish; Worden, Alexandra Z; Lagarias, J Clark

    2014-03-11

    Plant phytochromes are photoswitchable red/far-red photoreceptors that allow competition with neighboring plants for photosynthetically active red light. In aquatic environments, red and far-red light are rapidly attenuated with depth; therefore, photosynthetic species must use shorter wavelengths of light. Nevertheless, phytochrome-related proteins are found in recently sequenced genomes of many eukaryotic algae from aquatic environments. We examined the photosensory properties of seven phytochromes from diverse algae: four prasinophyte (green algal) species, the heterokont (brown algal) Ectocarpus siliculosus, and two glaucophyte species. We demonstrate that algal phytochromes are not limited to red and far-red responses. Instead, different algal phytochromes can sense orange, green, and even blue light. Characterization of these previously undescribed photosensors using CD spectroscopy supports a structurally heterogeneous chromophore in the far-red-absorbing photostate. Our study thus demonstrates that extensive spectral tuning of phytochromes has evolved in phylogenetically distinct lineages of aquatic photosynthetic eukaryotes. PMID:24567382

  3. School, Community Leadership, and Election Structure

    ERIC Educational Resources Information Center

    Allen, Ann

    2008-01-01

    This article examines how the political structure of school elections contributes to leadership perspectives related to school-community engagement. Interview data from school superintendents, school board presidents, and city mayors across four cities and two election types were analyzed to determine if differences in school election structure…

  4. Emergence of structured communities through evolutionary dynamics.

    PubMed

    Shtilerman, Elad; Kessler, David A; Shnerb, Nadav M

    2015-10-21

    Species-rich communities, in which many competing species coexist in a single trophic level, are quite frequent in nature, but pose a formidable theoretical challenge. In particular, it is known that complex competitive systems become unstable and unfeasible when the number of species is large. Recently, many studies have attributed the stability of natural communities to the structure of the interspecific interaction network, yet the nature of such structures and the underlying mechanisms responsible for them remain open questions. Here we introduce an evolutionary model, based on the generic Lotka-Volterra competitive framework, from which a stable, structured, diverse community emerges spontaneously. The modular structure of the competition matrix reflects the phylogeny of the community, in agreement with the hierarchial taxonomic classification. Closely related species tend to have stronger niche overlap and weaker fitness differences, as opposed to pairs of species from different modules. The competitive-relatedness hypothesis and the idea of emergent neutrality are discussed in the context of this evolutionary model. PMID:26231415

  5. Phylogenetic structure in tropical hummingbird communities

    PubMed Central

    Graham, Catherine H.; Parra, Juan L.; Rahbek, Carsten; McGuire, Jimmy A.

    2009-01-01

    How biotic interactions, current and historical environment, and biogeographic barriers determine community structure is a fundamental question in ecology and evolution, especially in diverse tropical regions. To evaluate patterns of local and regional diversity, we quantified the phylogenetic composition of 189 hummingbird communities in Ecuador. We assessed how species and phylogenetic composition changed along environmental gradients and across biogeographic barriers. We show that humid, low-elevation communities are phylogenetically overdispersed (coexistence of distant relatives), a pattern that is consistent with the idea that competition influences the local composition of hummingbirds. At higher elevations communities are phylogenetically clustered (coexistence of close relatives), consistent with the expectation of environmental filtering, which may result from the challenge of sustaining an expensive means of locomotion at high elevations. We found that communities in the lowlands on opposite sides of the Andes tend to be phylogenetically similar despite their large differences in species composition, a pattern implicating the Andes as an important dispersal barrier. In contrast, along the steep environmental gradient between the lowlands and the Andes we found evidence that species turnover is comprised of relatively distantly related species. The integration of local and regional patterns of diversity across environmental gradients and biogeographic barriers provides insight into the potential underlying mechanisms that have shaped community composition and phylogenetic diversity in one of the most species-rich, complex regions of the world. PMID:19805042

  6. Phylogenetic structure in tropical hummingbird communities.

    PubMed

    Graham, Catherine H; Parra, Juan L; Rahbek, Carsten; McGuire, Jimmy A

    2009-11-17

    How biotic interactions, current and historical environment, and biogeographic barriers determine community structure is a fundamental question in ecology and evolution, especially in diverse tropical regions. To evaluate patterns of local and regional diversity, we quantified the phylogenetic composition of 189 hummingbird communities in Ecuador. We assessed how species and phylogenetic composition changed along environmental gradients and across biogeographic barriers. We show that humid, low-elevation communities are phylogenetically overdispersed (coexistence of distant relatives), a pattern that is consistent with the idea that competition influences the local composition of hummingbirds. At higher elevations communities are phylogenetically clustered (coexistence of close relatives), consistent with the expectation of environmental filtering, which may result from the challenge of sustaining an expensive means of locomotion at high elevations. We found that communities in the lowlands on opposite sides of the Andes tend to be phylogenetically similar despite their large differences in species composition, a pattern implicating the Andes as an important dispersal barrier. In contrast, along the steep environmental gradient between the lowlands and the Andes we found evidence that species turnover is comprised of relatively distantly related species. The integration of local and regional patterns of diversity across environmental gradients and biogeographic barriers provides insight into the potential underlying mechanisms that have shaped community composition and phylogenetic diversity in one of the most species-rich, complex regions of the world. PMID:19805042

  7. The nested structure of a scavenger community

    PubMed Central

    Selva, Nuria; Fortuna, Miguel A

    2007-01-01

    Scavenging is a widespread phenomenon in vertebrate communities which has rarely been accounted for, in spite of playing an essential role in food webs by enhancing nutrient recycling and community stability. Most studies on scavenger assemblages have often presented an oversimplified view of carrion foraging. Here, we applied for the first time the concept of nestedness to the study of a species-rich scavenger community in a forest ecosystem (Białowieża Primeval Forest, Poland) following a network approach. By analysing one of the most complete datasets existing up to now in a pristine environment, we have shown that the community of facultative scavengers is not randomly assembled but highly nested. A nested pattern means that species-poor carcasses support a subset of the scavenger assemblage occurring at progressively species-rich carcasses. This result contradicts the conventional view of facultative scavenging as random and opportunistic and supports recent findings in scavenging ecology. It also suggests that factors other than competition play a major role in determining community structure. Nested patterns in scavenger communities appear to be promoted by the high diversity in carrion resources and consumers, the differential predictability of the ungulate carcass types and stressful environmental conditions. PMID:17301021

  8. Community structure and dynamics in social systems

    NASA Astrophysics Data System (ADS)

    Wilkinson, Dennis M.

    This thesis presents applications of statistical physics to the study of the structure and dynamics of social systems, that is, systems whose interactions are based on information exchange. Social systems typically possess a community structure arising from the self organization of groups of interacting components into tightly-knit clusters. An automated method of identifying communities within a network of interactions is first presented. The method includes a statistical component crucial to obtaining accurate results in large, complex systems. It is applied to two real-world social networks, a network of email interactions and a network of related articles in the biomedical literature. The clusters it identifies within these networks are shown to correspond to communities of interrelated components. Next, the dynamics of cooperative problem solving processes on social systems are studied. A simple stochastic model is proposed which captures key aspects of the dynamics which have been empirically observed. Most important among these are the increase in average time to solution and in likelihood of long delays as the system size increases, as well as the log-normal distribution of times to solution. It is shown that a community structure both reduces the average time to solution and decreases the probability of delay. In cases where a system of cooperative efforts does not possess an inherent community structure, the effect of imposing communities is examined. The factor which most affects the dynamics when communities are imposed is shown to be the degree to which individuals neglect information from outside their own communities. The theory of stochastic vector processes is central to the dynamics of social systems and a mathematical study of this subject is presented. Expressions describing the evolution of the moments in the neighborhood of fixed points are obtained for arbitrary systems. Approximation techniques are applied in the small and large noise limits

  9. Information transfer in community structured multiplex networks

    NASA Astrophysics Data System (ADS)

    Solé Ribalta, Albert; Granell, Clara; Gómez, Sergio; Arenas, Alex

    2015-08-01

    The study of complex networks that account for different types of interactions has become a subject of interest in the last few years, specially because its representational power in the description of users interactions in diverse online social platforms (Facebook, Twitter, Instagram, etc.). The mathematical description of these interacting networks has been coined under the name of multilayer networks, where each layer accounts for a type of interaction. It has been shown that diffusive processes on top of these networks present a phenomenology that cannot be explained by the naive superposition of single layer diffusive phenomena but require the whole structure of interconnected layers. Nevertheless, the description of diffusive phenomena on multilayer networks has obviated the fact that social networks have strong mesoscopic structure represented by different communities of individuals driven by common interests, or any other social aspect. In this work, we study the transfer of information in multilayer networks with community structure. The final goal is to understand and quantify, if the existence of well-defined community structure at the level of individual layers, together with the multilayer structure of the whole network, enhances or deteriorates the diffusion of packets of information.

  10. Harmful Algal Blooms (HABs)

    MedlinePlus

    ... Topics Eighth Annual National Conference on Health Communication, Marketing & Media August 19-21, 2014 Atlanta, GA Harmful Algal Blooms Recommend on Facebook Tweet Share Compartir On this Page What's the ...

  11. Identifying community structure in complex networks

    NASA Astrophysics Data System (ADS)

    Shao, Chenxi; Duan, Yubing

    2015-07-01

    A wide variety of applications could be formulated to resolve the problem of finding all communities from a given network, ranging from social and biological network analysis to web mining and searching. In this study, we propose the concept of virtual attractive strength between each pair of node in networks, and then give the definition of community structure based on the proposed attractive strength. Furthermore, we present a community detection method by moving vertices to the clusters that produce the largest attractive strengths to them until the division of network reaches unchanged. Experimental results on synthetic and real networks indicate that the proposed approach has favorite effectiveness and fast convergence speed, which provides an efficient method for exploring and analyzing complex systems.

  12. Modularity and community structure in networks.

    PubMed

    Newman, M E J

    2006-06-01

    Many networks of interest in the sciences, including social networks, computer networks, and metabolic and regulatory networks, are found to divide naturally into communities or modules. The problem of detecting and characterizing this community structure is one of the outstanding issues in the study of networked systems. One highly effective approach is the optimization of the quality function known as "modularity" over the possible divisions of a network. Here I show that the modularity can be expressed in terms of the eigenvectors of a characteristic matrix for the network, which I call the modularity matrix, and that this expression leads to a spectral algorithm for community detection that returns results of demonstrably higher quality than competing methods in shorter running times. I illustrate the method with applications to several published network data sets. PMID:16723398

  13. A multi-decade time series of kelp forest community structure at San Nicolas Island, California

    USGS Publications Warehouse

    Lafferty, Kevin D.; Kenner, Michael C.; Estes, James A.; Tinker, M. Tim; Bodkin, James L.; Cowen, Robert K.; Harrold, Christopher; Novak, Mark; Rassweiler, Andrew; Reed, Daniel C.

    2013-01-01

    San Nicolas Island is surrounded by broad areas of shallow subtidal habitat, characterized by dynamic kelp forest communities that undergo dramatic and abrupt shifts in community composition. Although these reefs are fished, the physical isolation of the island means that they receive less impact from human activities than most reefs in Southern California, making San Nicolas an ideal place to evaluate alternative theories about the dynamics of these communities. Here we present monitoring data from seven sampling stations surrounding the island, including data on fish, invertebrate, and algal abundance. These data are unusual among subtidal monitoring data sets in that they combine relatively frequent sampling (twice per year) with an exceptionally long time series (since 1980). Other outstanding qualities of the data set are the high taxonomic resolution captured and the monitoring of permanent quadrats and swaths where the history of the community structure at specific locations has been recorded through time. Finally, the data span a period that includes two of the strongest ENSO events on record, a major shift in the Pacific decadal oscillation, and the reintroduction of sea otters to the island in 1987 after at least 150 years of absence. These events provide opportunities to evaluate the effects of bottom-up forcing, top-down control, and physical disturbance on shallow rocky reef communities.

  14. [Phytoplankton pigment patterns and community structure in the Yangtze Estuary and its adjacent areas].

    PubMed

    Lai, Jun-xiang; Yu, Zhi-ming; Song, Xiu-xian; Han, Xiao-tian; Cao, Xi-hua; Yuan, Yong-quan

    2013-09-01

    Three cruises were carried out in the Yangtze Estuary and its adjacent areas in May, November, June during 2009-2010. The spatial variations of phytoplankton community structure were investigated based on RP-HPLC analysis of pigments and CHEMTAX processing of the pigment data. 21 kinds of pigments were detected, among which chlorophyll a, peridinin, fucoxanthin, 19'-butanoyloxyfucoxanthin, 19'-hexanoyloxyfucoxanthin, chlorophyll b, diadinoxanthin, alloxanthin and zeaxanthin were the major pigments in the Yangtze Estuary and its adjacent areas. Chlorophyll a was the most abundant in all pigments, followed by fuxoxanthin. Other pigments generally contributed a minor proportion to the total pigments. High concentrations of fucoxanthin and peridinin were observed in May 2009 and June 2010, indicating blooms of diatoms and dinoflagellates. The results showed that the composition and distribution of phytoplankton pigments were influenced by environmental factors. The phytoplankton community, as determined by biomarker pigment concentration using HPLC and CHEMTAX, was composed mainly of diatoms, dinoflagellates, cryptophytes, chlorophytes, cyanobacteria, prymnesiophytes, chrysophytes and prasinophytes. The dominant algal groups were diatoms, dinoflagellates and chlorophytes in May 2009. The phytoplankton community was characterized by high contribution of diatoms in November 2009. Diatoms, dinoflagellates and cryptophytes accounted for 62.5% of chlorophyll a in June 2010, and the relative abundance of cyanobacteria was higher in this cruise. The spatial variations of phytoplankton community structure featured distinct regionality. Diatoms, chlorophytes and cryptophytes were the main groups in the inshore waters, and the abundances of prymnesiophytes, chrysophytes and cyanobacteria were increasing from inshore to the open sea. PMID:24288983

  15. A cheating limit for structured communities

    SciTech Connect

    Perelson, Alan S; Gerrish, Philip J

    2008-01-01

    The constructive creativity of natural selection originates from its paradoxical ability to foster cooperation through competition. Cooperating communities ranging from complex societies to somatic tissue are constantly under attack, however, by non-cooperating mutants or transformants, called 'cheaters'. Structure in these communities promotes the formation of cooperating clusters whose competitive superiority can alone be sufficient to thwart outgrowths of cheaters and thereby maintain cooperation. But we find that when cheaters appear too frequently -- exceeding a threshold mutation or transformation rate -- their scattered outgrowths infiltrate and break up cooperating clusters, resulting in a cascading loss of community integrity, a switch to net positive selection for cheaters, and ultimately in the loss of cooperation. We find that this threshold mutation rate is directly proportional to the fitness support received from each cooperating neighbor minus the individual fitness benefit of cheating. When mutation rate also evolves, this threshold is crossed spontaneously after thousands of generations, at which point cheaters rapidly invade. In a structured community, cooperation can persist only if the mutation rate remains below a critical value.

  16. Taxonomies of networks from community structure

    NASA Astrophysics Data System (ADS)

    Onnela, Jukka-Pekka; Fenn, Daniel J.; Reid, Stephen; Porter, Mason A.; Mucha, Peter J.; Fricker, Mark D.; Jones, Nick S.

    2012-09-01

    The study of networks has become a substantial interdisciplinary endeavor that encompasses myriad disciplines in the natural, social, and information sciences. Here we introduce a framework for constructing taxonomies of networks based on their structural similarities. These networks can arise from any of numerous sources: They can be empirical or synthetic, they can arise from multiple realizations of a single process (either empirical or synthetic), they can represent entirely different systems in different disciplines, etc. Because mesoscopic properties of networks are hypothesized to be important for network function, we base our comparisons on summaries of network community structures. Although we use a specific method for uncovering network communities, much of the introduced framework is independent of that choice. After introducing the framework, we apply it to construct a taxonomy for 746 networks and demonstrate that our approach usefully identifies similar networks. We also construct taxonomies within individual categories of networks, and we thereby expose nontrivial structure. For example, we create taxonomies for similarity networks constructed from both political voting data and financial data. We also construct network taxonomies to compare the social structures of 100 Facebook networks and the growth structures produced by different types of fungi.

  17. Taxonomies of networks from community structure

    PubMed Central

    Reid, Stephen; Porter, Mason A.; Mucha, Peter J.; Fricker, Mark D.; Jones, Nick S.

    2014-01-01

    The study of networks has become a substantial interdisciplinary endeavor that encompasses myriad disciplines in the natural, social, and information sciences. Here we introduce a framework for constructing taxonomies of networks based on their structural similarities. These networks can arise from any of numerous sources: they can be empirical or synthetic, they can arise from multiple realizations of a single process (either empirical or synthetic), they can represent entirely different systems in different disciplines, etc. Because mesoscopic properties of networks are hypothesized to be important for network function, we base our comparisons on summaries of network community structures. Although we use a specific method for uncovering network communities, much of the introduced framework is independent of that choice. After introducing the framework, we apply it to construct a taxonomy for 746 networks and demonstrate that our approach usefully identifies similar networks. We also construct taxonomies within individual categories of networks, and we thereby expose nontrivial structure. For example, we create taxonomies for similarity networks constructed from both political voting data and financial data. We also construct network taxonomies to compare the social structures of 100 Facebook networks and the growth structures produced by different types of fungi. PMID:23030977

  18. Epidemic spreading on complex networks with community structures

    NASA Astrophysics Data System (ADS)

    Stegehuis, Clara; van der Hofstad, Remco; van Leeuwaarden, Johan S. H.

    2016-07-01

    Many real-world networks display a community structure. We study two random graph models that create a network with similar community structure as a given network. One model preserves the exact community structure of the original network, while the other model only preserves the set of communities and the vertex degrees. These models show that community structure is an important determinant of the behavior of percolation processes on networks, such as information diffusion or virus spreading: the community structure can both enforce as well as inhibit diffusion processes. Our models further show that it is the mesoscopic set of communities that matters. The exact internal structures of communities barely influence the behavior of percolation processes across networks. This insensitivity is likely due to the relative denseness of the communities.

  19. Epidemic spreading on complex networks with community structures

    PubMed Central

    Stegehuis, Clara; van der Hofstad, Remco; van Leeuwaarden, Johan S. H.

    2016-01-01

    Many real-world networks display a community structure. We study two random graph models that create a network with similar community structure as a given network. One model preserves the exact community structure of the original network, while the other model only preserves the set of communities and the vertex degrees. These models show that community structure is an important determinant of the behavior of percolation processes on networks, such as information diffusion or virus spreading: the community structure can both enforce as well as inhibit diffusion processes. Our models further show that it is the mesoscopic set of communities that matters. The exact internal structures of communities barely influence the behavior of percolation processes across networks. This insensitivity is likely due to the relative denseness of the communities. PMID:27440176

  20. Epidemic spreading on complex networks with community structures.

    PubMed

    Stegehuis, Clara; van der Hofstad, Remco; van Leeuwaarden, Johan S H

    2016-01-01

    Many real-world networks display a community structure. We study two random graph models that create a network with similar community structure as a given network. One model preserves the exact community structure of the original network, while the other model only preserves the set of communities and the vertex degrees. These models show that community structure is an important determinant of the behavior of percolation processes on networks, such as information diffusion or virus spreading: the community structure can both enforce as well as inhibit diffusion processes. Our models further show that it is the mesoscopic set of communities that matters. The exact internal structures of communities barely influence the behavior of percolation processes across networks. This insensitivity is likely due to the relative denseness of the communities. PMID:27440176

  1. Macroinvertebrate and algal community sample collection methods and data collected at selected sites in the Eagle River watershed, Colorado, 2000-07

    USGS Publications Warehouse

    Zuellig, Robert E.; Bruce, James F.

    2010-01-01

    State and local agencies are concerned about the effects of increasing urban development and human population growth on water quality and the biological condition of regional streams in the Eagle River watershed. In response to these needs, the U.S. Geological Survey initiated a study in cooperation with the Colorado River Water Conservation District, Eagle County, Eagle River Water and Sanitation District, Upper Eagle Regional Water Authority, Colorado Department of Transportation, City of Aurora, Town of Eagle, Town of Gypsum, Town of Minturn, Town of Vail, Vail Resorts, Colorado Springs Utilities, Denver Water, and the U.S. Department of Agriculture Forest Service. As part of this study, previously collected macroinvertebrate and algal data from the Eagle River watershed were compiled. This report includes macroinvertebrate data collected by the U.S. Geological Survey and(or) the U.S. Department of Agriculture Forest Service from 73 sites from 2000 to 2007 and algal data collected from up to 26 sites between 2000 and 2001 in the Eagle River watershed. Additionally, a brief description of the sample collection methods and data processing procedures are presented.

  2. Relations of Principal Components Analysis Site Scores to Algal-Biomass, Habitat, Basin-Characteristics, Nutrient, and Biological-Community Data in the Whitewater River and East Fork White River Basins, Indiana, 2002

    USGS Publications Warehouse

    Caskey, Brian J.; Frey, Jeffrey W.; Lowe, B. Scott

    2007-01-01

    Data were gathered from May through September 2002 at 76 randomly selected sites in the Whitewater River and East Fork White River Basins, Indiana, for algal biomass, habitat, nutrients, and biological communities (fish and invertebrates). Basin characteristics (land use and drainage area) and biolog-ical-community attributes and metric scores were determined for the basin of each sampling site. Yearly Principal Compo-nents Analysis site scores were calculated for algal biomass (periphyton and seston). The yearly Principal Components Analysis site scores for the first axis (PC1) were related using Spearman's rho to the seasonal algal-biomass, basin-charac-teristics, habitat, seasonal nutrient, and biological-community attribute and metric score data. The periphyton PC1 site score was not significantly related to the nine habitat or 12 nutrient variables examined. One land-use variable, drainage area, was negatively related to the periphyton PC1. Of the 43 fish-community attributes and metrics examined, the periphyton PC1 was negatively related to one attribute (large-river percent) and one metric score (car-nivore percent metric score). It was positively related to three fish-community attributes (headwater percent, pioneer percent, and simple lithophil percent). The periphyton PC1 was not statistically related to any of the 21 invertebrate-community attributes or metric scores examined. Of the 12 nutrient variables examined two were nega-tively related to the seston PC1 site score in two seasons: total Kjeldahl nitrogen (July and September), and TP (May and September). There were no statistically significant relations between the seston PC1 and the five basin-characteristics or nine habitat variables examined. Of the 43 fish-community attributes and metrics examined, the seston PC1 was positively related to one attribute (headwater percent) and negatively related to one metric score (large-river percent metric score) . Of the 21 invertebrate-community attributes

  3. Relations of Principal Components Analysis Site Scores to Algal-Biomass, Habitat, Basin-Characteristics, Nutrient, and Biological-Community Data in the West Fork White River Basin, Indiana, 2001

    USGS Publications Warehouse

    Frey, Jeffrey W.; Caskey, Brian J.; Lowe, B. Scott

    2007-01-01

    Data were gathered from July through September 2001 at 34 randomly selected sites in the West Fork White River Basin, Indiana for algal biomass, habitat, nutrients, and biological communities (fish and invertebrates). Basin characteristics (drainage area and land use) and biological-community attributes and metric scores were determined for the basin of each sampling site. Yearly Principal Components Analysis site scores were calculated for algal biomass (periphyton and seston). The yearly Principal Components Analysis site scores for the first axis (PC1) were related, using Spearman's rho, to the seasonal algal-biomass, basin-characteristics, habitat, seasonal nutrient, biological-community attribute and metric score data. The periphyton PC1 site score, which was most influenced by ash-free dry mass, was negatively related to one (percent closed canopy) of nine habitat variables examined. Of the 43 fish-community attributes and metric scores examined, the periphyton PC1 was positively related to one fish-community attribute (percent tolerant). Of the 21 invertebrate-community attributes and metric scores examined, the periphyton PC1 was positively related to one attribute (Ephemeroptera, Plecoptera, and Trichoptera (EPT) index) and one metric score (EPT index metric score). The periphyton PC1 was not related to the five basin-characteristic or 12 nutrient variables examined. The seston PC1 site score, which was most influenced by particulate organic carbon, was negatively related to two of the 12 nutrient variables examined: total Kjeldahl nitrogen (July) and total phosphorus (July). Of the 43 fish-community attributes and metric scores examined, the seston PC1 was negatively related to one attribute (large-river percent). Of the 21 invertebrate-community attributes and metric scores examined, the seston PC1 was negatively related to one attribute (EPT-to-total ratio). The seston PC1 was not related to the five basin-characteristics or nine habitat variables

  4. Cell-free expression of the APP transmembrane fragments with Alzheimer's disease mutations using algal amino acid mixture for structural NMR studies.

    PubMed

    Bocharova, Olga V; Urban, Anatoly S; Nadezhdin, Kirill D; Bocharov, Eduard V; Arseniev, Alexander S

    2016-07-01

    Structural investigations need ready supply of the isotope labeled proteins with inserted mutations n the quantities sufficient for the heteronuclear NMR. Though cell-free expression system has been widely used in the past years, high startup cost and complex compound composition prevent many researches from the developing this technique, especially for membrane protein production. Here we demonstrate the utility of a robust, cost-optimized cell-free expression technique for production of the physiologically important transmembrane fragment of amyloid precursor protein, APP686-726, containing Alzheimer's disease mutations in the juxtamembrane (E693G, Arctic form) and the transmembrane parts (V717G, London form, or L723P, Australian form). The protein cost was optimized by varying the FM/RM ratio as well as the amino acid concentration. We obtained the wild-type and mutant transmembrane fragments in the pellet mode of continuous exchange cell-free system consuming only commercial algal mixture of the (13)C,(15)N-labeled amino acids. Scaling up analytical tests, we achieved milligram quantity yields of isotope labeled wild-type and mutant APP686-726 for structural studies by high resolution NMR spectroscopy in membrane mimicking environment. The described approach has from 5 to 23-fold cost advantage over the bacterial expression methods described earlier and 1.5 times exceeds our previous result obtained with the longer APP671-726WT fragment. PMID:27071311

  5. Community-oriented support and research structures

    NASA Astrophysics Data System (ADS)

    Attig, Norbert; Eickermann, Thomas; Gibbon, Paul; Lippert, Thomas

    2009-07-01

    Coordinated by the Partnership for Advanced Computing in Europe (PRACE) Europe is restructuring and strengthening its high-performance computing infrastructure with the aim to create a model HPC ecosystem. At the tip of the pyramid, up to six centres are envisaged that will operate systems of the highest performance class. The HPC Research Infrastructure (HPC-RI) will comprise European, national and regional centres. Science communities are integral partners, strong links will include Grid and Cloud users. The HPC-RI strives at providing scientists all over Europe, on the one hand, with unlimited and independent access to state-of-the-art computer resources in all performance classes and, on the other hand, with a world-class pan-European competence and support network. While the hardware-oriented buildup of the infrastructure is making progress, high-quality user support and software development in the upcoming era of unprecedented parallelism and exascale on the horizon have become the imminent challenges. This has been clearly recognized by the European Commission, who will issue calls for proposals to fund petascale software development in summer 2009. Although traditional support structures are well established in Europe's major supercomputing centres, it is questionable if these structures are able to meet the challenges of the future: in general, support structures are based on cross-disciplinary computer science and mathematics teams; disciplinary computational science support usually is given in an ad-hoc, project-oriented manner. In this paper, we describe our approach to establish a suitable support structure-Simulation Laboratories (SL). SLs are currently being established at the Jülich Supercomputing Centre of the Forschungszentrum Jülich (FZJ) and at the Steinbuch Centre for Computing (SCC) of the Karlsruhe Institute for Technology (KIT) in Germany. While SLs are community-oriented, i.e. each SL focusses on a specific community, they are structured

  6. [Structural variability of the lithorheophile macrobenthos communities].

    PubMed

    Chertoprud, M V

    2007-01-01

    The relationship between the abundance of taxa and life forms of lithorheophile macrobenthos and its variability were studied based on 200 quantitative samples from six territories of the Palaearctic (Moscow province, northwestern Caucasus, eastern Carpathians, northern Karelia, South Urals, and Altai mountains). The set of taxa predominant in the communities and their ecology are described. It is found that community structure varies strongly, depending on the characteristics of each region, on the size of the watercourse, and on the season. Six types of biocenoses are recognized by means of the Braun-Blanquet method, each characterized by its peculiar set of predominant life forms and families rather similar in different territories. The differences between these types are related to the size and the hydrological conditions of the watercourse. Biocenosis 1 is typical to smal brooks (up to 0.01-0.1 m3/s), characterised by the predominance of detritophagous animals non-specific to the type of food (Gammarus, Nemoura, Limnephilidae). In biocenosis 2a (large brooks with water flow 0.03-0.3 m3/s and velocity 0.1-0.3 m/s), almost immobile shell scrapers (Ancylus, Silo, Agapetes, Glossosoma) are predominant. Biocenosis 2b (large brooks with velocity 0.3-0.5 m/s) have a more or less balanced set of fundamental lithorheophile life forms. Biocenosis 2c (large mountain brooks with velocity 0.5-1 m/s) is characterised by specialized scrapers of the rapids (Epeorus and Diomesa) and filterers (Simuliidae). In biocenosis 3 (small rivers), sedentary filterers (Hydropsychidae, Simulliidae) are predominant; scrapers also play a significant role. Biocenosis 4 (rivers with water flow more than 3 m3/s, thick incrustations, and silted stones on the bottom) has predominant filterers (Hydropsychidae) and vermiform algophagous animals inside the incrustations (Orthocladius, Psychomyia). Significant variability in community structure unrelated to the environmental factors is revealed

  7. Submesoscale dynamics and planktonic community structure

    NASA Astrophysics Data System (ADS)

    Franks, P. J.; Taniguchi, D. A.

    2012-12-01

    The vertical velocities associated with submesoscale dynamics occur on time scales that are resonant with planktonic growth and grazing rates. This resonance may cause submesoscale dynamics to be disproportionately important to planktonic productivity and carbon sequestration. To investigate the role of submesoscale motions on planktonic community structure, we used a continuum size-structured planktonic ecosystem model. The model is based on a traditional NPZ framework, but allows for size dependence of all biological processes. The model was carefully parameterized with data from the literature, and reproduces realistic planktonic size spectra. Perturbing the model with a nutrient pulse similar to that driven by submesoscale upwelling leads to significant perturbations to the ecosystem. Pulses of enhanced biomass propagate from small to large organisms over time scales of days to weeks. We explore the model stability and dynamics, and their dependence on the parameter values, to gain understanding of the potential for submesoscale physical motions to influence planktonic ecosystem dynamics.

  8. Algal Biofuels Fact Sheet

    SciTech Connect

    2009-10-27

    This fact sheet provides information on algal biofuels, which are generating considerable interest around the world. They may represent a sustainable pathway for helping to meet the U.S. biofuel production targets set by the Energy Independence and Security Act of 2007.

  9. Purification and characterization of high- and low-molecular-mass isoforms of phosphoenolpyruvate carboxylase from Chlamydomonas reinhardtii. Kinetic, structural and immunological evidence that the green algal enzyme is distinct from the prokaryotic and higher plant enzymes.

    PubMed Central

    Rivoal, J; Plaxton, W C; Turpin, D H

    1998-01-01

    Phosphoenolpyruvate carboxylase (PEPC) is a key enzyme in the supply of carbon skeletons for the assimilation of nitrogen by green algae. Two PEPC isoforms with respective native molecular masses of 400 (PEPC1) and 650 (PEPC2) kDa have been purified from Chlamydomonas reinhardtii CW-15 cc1883 (Chlorophyceae). SDS/PAGE, immunoblot and CNBr peptide-mapping analyses indicate the presence of the same 100 kDa PEPC catalytic subunit in both isoforms. PEPC1 is a homotetramer, whereas PEPC2 seems to be a complex between the PEPC catalytic subunit and other immunologically unrelated polypeptides of 50-70 kDa. Kinetic analyses indicate that these PEPC isoforms are (1) differentially regulated by pH, (2) activated by glutamine and dihydroxyacetone phosphate and (3) inhibited by glutamate, aspartate, 2-oxoglutarate and malate. These results are consistent with the current model for the regulation of anaplerotic carbon fixation in green algae, and demonstrate that green algal PEPCs are uniquely regulated by glutamine. Several techniques were used to assess the structural relationships between C. reinhardtii PEPC and the higher plant or prokaryotic enzyme. Immunoblot studies using anti-(green algal or higher plant PEPC) IgGs suggested that green algal (C. reinhardtii, Selenastrum minutum), higher plant (maize, banana fruit, tobacco) and prokaryotic (Synechococcus leopoliensis, Escherichia coli) PEPCs have little or no immunological relatedness. Moreover, the N-terminal amino acid sequence of the C. reinhardtii PEPC subunit did not have significant similarity to the highly conserved corresponding region in enzymes from higher plants, and CNBr cleavage patterns of green algal PEPCs were distinct from those of higher plant and cyanobacterial PEPCs. These results point to significant evolutionary divergence between green algal, higher plant and prokaryotic PEPCs. PMID:9512480

  10. Community Attachment and Satisfaction: The Role of a Community's Social Network Structure

    ERIC Educational Resources Information Center

    Crowe, Jessica

    2010-01-01

    This paper links the micro and macro levels of analysis by examining how different aspects of community sentiment are affected by one's personal ties to the community compared with the organizational network structure of the community. Using data collected from residents of six communities in Washington State, network analysis combined with…

  11. Influence of phosphorus availability on the community structure and physiology of cultured biofilms.

    PubMed

    Li, Shuangshuang; Wang, Chun; Qin, Hongjie; Li, Yinxia; Zheng, Jiaoli; Peng, Chengrong; Li, Dunhai

    2016-04-01

    Biofilms have important effects on nutrient cycling in aquatic ecosystems. However, publications about the community structure and functions under laboratory conditions are rare. This study focused on the developmental and physiological properties of cultured biofilms under various phosphorus concentrations performed in a closely controlled continuous flow incubator. The results showed that the biomass (Chl a) and photosynthesis of algae were inhibited under P-limitation conditions, while the phosphatase activity and P assimilation rate were promoted. The algal community structure of biofilms was more likely related to the colonization stage than with the phosphorus availability. Cyanobacteria were more competitive than other algae in biofilms, particularly when cultured under low P levels. A dominance shift occurred from non-filamentous algae in the early stage to filamentous algae in the mid and late stages under P concentrations of 0.01, 0.1 and 0.6 mg/L. However, the total N content, dry weight biomass and bacterial community structure of biofilms were unaffected by phosphorus availability. This may be attributed to the low respiration rate, high accumulation of extracellular polymeric substances and high alkaline phosphatase activity in biofilms when phosphorus availability was low. The bacterial community structure differed over time, while there was little difference between the four treatments, which indicated that it was mainly affected by the colonization stage of the biofilms rather than the phosphorus availability. Altogether, these results suggested that the development of biofilms was influenced by the phosphorus availability and/or the colonization stage and hence determined the role that biofilms play in the overlying water. PMID:27090691

  12. Common community structure in time-varying networks

    NASA Astrophysics Data System (ADS)

    Zhang, Shihua; Zhao, Junfei; Zhang, Xiang-Sun

    2012-05-01

    In this report we introduce the concept of common community structure in time-varying networks. We propose a novel optimization algorithm to rapidly detect common community structure in such networks. Both theoretical and numerical results show that the proposed method not only can resolve detailed common communities, but also can effectively identify the dynamical phenomena in time-varying networks.

  13. Virioplankton Community Structure in Tunisian Solar Salterns

    PubMed Central

    Boujelben, Ines; Yarza, Pablo; Almansa, Cristina; Villamor, Judith; Maalej, Sami; Santos, Fernando

    2012-01-01

    The microbial community inhabiting Sfax solar salterns on the east coast of Tunisia has been studied by means of different molecular and culture-dependent tools that have unveiled the presence of novel microbial groups as well as a community structure different from that of other coastal hypersaline environments. We have focused on the study of the viral assemblages of these salterns and their changes along the salinity gradient and over time. Viruses from three ponds (C4, M1, and TS) encompassing salinities from moderately hypersaline to saturated (around 14, 19, and 35%, respectively) were sampled in May and October 2009 and analyzed by transmission electron microscopy (TEM) and pulsed-field gel electrophoresis (PFGE). Additionally, for all three October samples and the May TS sample, viral metagenomic DNA was cloned in fosmids, end sequenced, and analyzed. Viral concentration, as well as virus-to-cell ratios, increased along the salinity gradient, with around 1010 virus-like particles (VLPs)/ml in close-to-saturation ponds, which represents the highest viral concentration reported so far for aquatic systems. Four distinct morphologies could be observed with TEM (spherical, tailed, spindled, and filamentous) but with various proportions in the different samples. Metagenomic analyses indicated that every pond harbored a distinct viral assemblage whose G+C content could be roughly correlated with that of the active part of the microbial community that may have constituted the putative hosts. As previously reported for hypersaline metaviromes, most sequences did not have matches in the databases, although some were conserved among the Sfax metaviromes. BLASTx, BLASTp, and dinucleotide frequency analyses indicated that (i) factors additional to salinity could be structuring viral communities and (ii) every metavirome had unique gene contents and dinucleotide frequencies. Comparison with hypersaline metaviromes available in the databases indicated that the viral

  14. Community Structure and Vietnamese Refugee Adaptation: The Significance of Context.

    ERIC Educational Resources Information Center

    Starr, Paul D.; Roberts, Alden E.

    1982-01-01

    Describes research investigating the effects of community structure on the adjustment of Vietnamese refugees in America. Emphasizes how congruence between individual characteristics and characteristics of the receiving community determine successful refugee adaptation to a new environment. (MJL)

  15. Bipartite Community Structure of eQTLs.

    PubMed

    Platig, John; Castaldi, Peter J; DeMeo, Dawn; Quackenbush, John

    2016-09-01

    Genome Wide Association Studies (GWAS) and expression quantitative trait locus (eQTL) analyses have identified genetic associations with a wide range of human phenotypes. However, many of these variants have weak effects and understanding their combined effect remains a challenge. One hypothesis is that multiple SNPs interact in complex networks to influence functional processes that ultimately lead to complex phenotypes, including disease states. Here we present CONDOR, a method that represents both cis- and trans-acting SNPs and the genes with which they are associated as a bipartite graph and then uses the modular structure of that graph to place SNPs into a functional context. In applying CONDOR to eQTLs in chronic obstructive pulmonary disease (COPD), we found the global network "hub" SNPs were devoid of disease associations through GWAS. However, the network was organized into 52 communities of SNPs and genes, many of which were enriched for genes in specific functional classes. We identified local hubs within each community ("core SNPs") and these were enriched for GWAS SNPs for COPD and many other diseases. These results speak to our intuition: rather than single SNPs influencing single genes, we see groups of SNPs associated with the expression of families of functionally related genes and that disease SNPs are associated with the perturbation of those functions. These methods are not limited in their application to COPD and can be used in the analysis of a wide variety of disease processes and other phenotypic traits. PMID:27618581

  16. Community Structure in Online Collegiate Social Networks

    NASA Astrophysics Data System (ADS)

    Traud, Amanda; Kelsic, Eric; Mucha, Peter; Porter, Mason

    2009-03-01

    Online social networking sites have become increasingly popular with college students. The networks we studied are defined through ``friendships'' indicated by Facebook users from UNC, Oklahoma, Caltech, Georgetown, and Princeton. We apply the tools of network science to study the Facebook networks from these five different universities at a single point in time. We investigate each single-institution network's community structure, which we obtain through partitioning the graph using an eigenvector method. We use both graphical and quantitative tools, including pair-counting methods, which we interpret through statistical analysis and permutation tests to measure the correlations between the network communities and a set of characteristics given by each user (residence, class year, major, and high school). We also analyze the single gender subsets of these networks, and the impact of missing demographical data. Our study allows us to compare the online social networks for the five schools as well as infer differences in offline social interactions. At the schools studied, we were able to define which characteristics of the Facebook users correlate best with friendships.

  17. The network of collaboration among rappers and its community structure

    NASA Astrophysics Data System (ADS)

    Smith, Reginald D.

    2006-02-01

    The social network formed by the collaboration between rappers is studied using standard statistical techniques for analysing complex networks. In addition, the community structure of the rap music community is analysed using a new method that uses weighted edges to determine which connections are most important and revealing among all the communities. The results of this method as well as possible reasons for the structure of the rap music community are discussed.

  18. Drifting algae and zoobenthos — Effects on settling and community structure

    NASA Astrophysics Data System (ADS)

    Bonsdorff, Erik

    Shallow (5 to 10 m) sandy bottoms in the Baltic Sea are important areas for zoobenthic production. The infaunal communities are generally governed by the hydrographical conditions are transport of the sediment through wind effects. With increasing eutrophication in the Baltic Sea, drifting mats of annual algae ( Cladophora, Stictyosiphon, Polysiphonia, Rhodemela, Sphacelaria, Pilayella, Furcellaria, Ceramium, etc) have become increasingly common, adding to the structuring and regulating factors for the infauna. In 1990 and 91, a field-study (SCUBA diving; zoobenthos and algae sampling) was carried out in the Åland archipelogo, in thennorthern and their structuring effect on the zoobenthos. Algal biomass increased from 150 ± 19 g DW·m -2 in 1990 to 832±60 g DW·m -2 in 1991, having no effect on oxygen saturation in 1990, but showing signs of reduced oxygen saturation in 1991. Organic content of the sediment remained stable (0.60 to 0.74%) during the entire study period. The zoobenthic community showed significant responses to the drifting algae at population level and in terms of community structure (by 1991: significantly reduced species number; low similarity values (40 to 65%) between bare sand and under the algae). The main species affected were the dominating bivalve Macoma balthica, the polychaetes Pygospio elegans and Manayunkia aestuarina, and the amphipod Corophium volutator. The settlement of M. balthica spat was significantly reduced by the algae (>70% in 1990/91), and no individuals of the dominating polychaetes were recorded under the mat. C. volutator, however, benefited from the algae, and greatly increased in numbers. The results clearly demonstrate the types of physical effects drift-algae will have no sandy-bottom benthos, and show that significant changes in the communities over large areas can be expected with increasing eutrophication.

  19. Algal populations controlled by fish herbivory across a wave exposure gradient on southern temperate shores.

    PubMed

    Taylor, David I; Schiel, David R

    2010-01-01

    Consumers that forage across habitats can affect communities by altering the abundance and distribution of key species. In marine communities, studies of trophic interactions have generally focused on the effects of herbivorous and predatory invertebrates on benthic algae and mussel populations. However, large mobile consumers that move across habitats, such as fishes, can strongly affect community dynamics through consumption of habitat-dominating species, but their effects often vary over environmental gradients. On temperate rocky shores, herbivorous fishes are generally a small part of the fish fauna compared to the tropics, and there is sparse evidence that they play a major direct role in algal community dynamics, particularly of large brown algae that dominate many reefs. In New Zealand, however, a wide-ranging herbivorous fish, Odax pullus, feeds exclusively on macroalgae, including Durvillaea antarctica, a large low-intertidal fucoid reaching 10 m in length and 70 kg in mass. In four experiments we tested the extent of fish herbivory and how it was affected by algal canopy structure across a gradient of wave exposure at multiple sites. Exclusion experiments showed that fish impacts greatly reduced the cover and biomass of Durvillaea and that these effects decreased with increasing wave stress and algal canopy cover, effectively restricting the alga to exposed conditions. Almost all plants were entirely removed by fish where there was a sparse algal canopy in sheltered and semi-exposed sites, but there was significantly less grazing in exposed sites. Recruit Durvillaea beneath canopies were less affected by fish grazing, but they grew slowly. Successful natural recruitment, therefore, occurred almost exclusively on exposed shores outside canopies where many plants escaped severe grazing, and growth to maturity was far greater than elsewhere. Such large and direct impacts on the local and regional distribution of large brown algal populations by mobile

  20. Spatial Patterns in Herbivory on a Coral Reef Are Influenced by Structural Complexity but Not by Algal Traits

    PubMed Central

    Vergés, Adriana; Vanderklift, Mathew A.; Doropoulos, Christopher; Hyndes, Glenn A.

    2011-01-01

    Background Patterns of herbivory can alter the spatial structure of ecosystems, with important consequences for ecosystem functions and biodiversity. While the factors that drive spatial patterns in herbivory in terrestrial systems are well established, comparatively less is known about what influences the distribution of herbivory in coral reefs. Methodology and Principal Findings We quantified spatial patterns of macroalgal consumption in a cross-section of Ningaloo Reef (Western Australia). We used a combination of descriptive and experimental approaches to assess the influence of multiple macroalgal traits and structural complexity in establishing the observed spatial patterns in macroalgal herbivory, and to identify potential feedback mechanisms between herbivory and macroalgal nutritional quality. Spatial patterns in macroalgal consumption were best explained by differences in structural complexity among habitats. The biomass of herbivorous fish, and rates of herbivory were always greater in the structurally-complex coral-dominated outer reef and reef flat habitats, which were also characterised by high biomass of herbivorous fish, low cover and biomass of macroalgae and the presence of unpalatable algae species. Macroalgal consumption decreased to undetectable levels within 75 m of structurally-complex reef habitat, and algae were most abundant in the structurally-simple lagoon habitats, which were also characterised by the presence of the most palatable algae species. In contrast to terrestrial ecosystems, herbivory patterns were not influenced by the distribution, productivity or nutritional quality of resources (macroalgae), and we found no evidence of a positive feedback between macroalgal consumption and the nitrogen content of algae. Significance This study highlights the importance of seascape-scale patterns in structural complexity in determining spatial patterns of macroalgal consumption by fish. Given the importance of herbivory in maintaining the

  1. Nutrient removal from horticultural wastewater by benthic filamentous algae Klebsormidium sp., Stigeoclonium spp. and their communities: From laboratory flask to outdoor Algal Turf Scrubber (ATS).

    PubMed

    Liu, Junzhuo; Danneels, Bram; Vanormelingen, Pieter; Vyverman, Wim

    2016-04-01

    Benthic filamentous algae have evident advantages in wastewater treatment over unicellular microalgae, including the ease in harvesting and resistance to predation. To assess the potentials of benthic filamentous algae in treating horticultural wastewater under natural conditions in Belgium, three strains and their mixture with naturally wastewater-borne microalgae were cultivated in 250 ml Erlenmeyer flasks in laboratory as well as in 1 m(2) scale outdoor Algal Turf Scrubber (ATS) with different flow rates. Stigeoclonium competed well with the natural wastewater-borne microalgae and contributed to most of the biomass production both in Erlenmeyer flasks and outdoor ATS at flow rates of 2-6 L min(-1) (water velocity 3-9 cm s(-1)), while Klebsormidium was not suitable for growing in horticultural wastewater under the tested conditions. Flow rate had great effects on biomass production and nitrogen removal, while phosphorus removal was less influenced by flow rate due to other mechanisms than assimilation by algae. PMID:26841229

  2. National Algal Biofuels Technology Roadmap

    SciTech Connect

    Ferrell, John; Sarisky-Reed, Valerie

    2010-05-01

    The framework for National Algal Biofuels Technology Roadmap was constructed at the Algal Biofuels Technology Roadmap Workshop, held December 9-10, 2008, at the University of Maryland-College Park. The Workshop was organized by the Biomass Program to discuss and identify the critical challenges currently hindering the development of a domestic, commercial-scale algal biofuels industry. This Roadmap presents information from a scientific, economic, and policy perspectives that can support and guide RD&D investment in algal biofuels. While addressing the potential economic and environmental benefits of using algal biomass for the production of liquid transportation fuels, the Roadmap describes the current status of algae RD&D. In doing so, it lays the groundwork for identifying challenges that likely need to be overcome for algal biomass to be used in the production of economically viable biofuels.

  3. Surprise maximization reveals the community structure of complex networks

    NASA Astrophysics Data System (ADS)

    Aldecoa, Rodrigo; Marín, Ignacio

    2013-01-01

    How to determine the community structure of complex networks is an open question. It is critical to establish the best strategies for community detection in networks of unknown structure. Here, using standard synthetic benchmarks, we show that none of the algorithms hitherto developed for community structure characterization perform optimally. Significantly, evaluating the results according to their modularity, the most popular measure of the quality of a partition, systematically provides mistaken solutions. However, a novel quality function, called Surprise, can be used to elucidate which is the optimal division into communities. Consequently, we show that the best strategy to find the community structure of all the networks examined involves choosing among the solutions provided by multiple algorithms the one with the highest Surprise value. We conclude that Surprise maximization precisely reveals the community structure of complex networks.

  4. Surprise maximization reveals the community structure of complex networks.

    PubMed

    Aldecoa, Rodrigo; Marín, Ignacio

    2013-01-01

    How to determine the community structure of complex networks is an open question. It is critical to establish the best strategies for community detection in networks of unknown structure. Here, using standard synthetic benchmarks, we show that none of the algorithms hitherto developed for community structure characterization perform optimally. Significantly, evaluating the results according to their modularity, the most popular measure of the quality of a partition, systematically provides mistaken solutions. However, a novel quality function, called Surprise, can be used to elucidate which is the optimal division into communities. Consequently, we show that the best strategy to find the community structure of all the networks examined involves choosing among the solutions provided by multiple algorithms the one with the highest Surprise value. We conclude that Surprise maximization precisely reveals the community structure of complex networks. PMID:23320141

  5. The Community Structure of the Global Corporate Network

    PubMed Central

    Vitali, Stefania; Battiston, Stefano

    2014-01-01

    We investigate the community structure of the global ownership network of transnational corporations. We find a pronounced organization in communities that cannot be explained by randomness. Despite the global character of this network, communities reflect first of all the geographical location of firms, while the industrial sector plays only a marginal role. We also analyze the meta-network in which the nodes are the communities and the links are obtained by aggregating the links among firms belonging to pairs of communities. We analyze the network centrality of the top 50 communities and we provide a quantitative assessment of the financial sector role in connecting the global economy. PMID:25126722

  6. The community structure of the global corporate network.

    PubMed

    Vitali, Stefania; Battiston, Stefano

    2014-01-01

    We investigate the community structure of the global ownership network of transnational corporations. We find a pronounced organization in communities that cannot be explained by randomness. Despite the global character of this network, communities reflect first of all the geographical location of firms, while the industrial sector plays only a marginal role. We also analyze the meta-network in which the nodes are the communities and the links are obtained by aggregating the links among firms belonging to pairs of communities. We analyze the network centrality of the top 50 communities and we provide a quantitative assessment of the financial sector role in connecting the global economy. PMID:25126722

  7. Similarity between community structures of different online social networks and its impact on underlying community detection

    NASA Astrophysics Data System (ADS)

    Fan, W.; Yeung, K. H.

    2015-03-01

    As social networking services are popular, many people may register in more than one online social network. In this paper we study a set of users who have accounts of three online social networks: namely Foursquare, Facebook and Twitter. Community structure of this set of users may be reflected in these three online social networks. Therefore, high correlation between these reflections and the underlying community structure may be observed. In this work, community structures are detected in all three online social networks. Also, we investigate the similarity level of community structures across different networks. It is found that they show strong correlation with each other. The similarity between different networks may be helpful to find a community structure close to the underlying one. To verify this, we propose a method to increase the weights of some connections in networks. With this method, new networks are generated to assist community detection. By doing this, value of modularity can be improved and the new community structure match network's natural structure better. In this paper we also show that the detected community structures of online social networks are correlated with users' locations which are identified on Foursquare. This information may also be useful for underlying community detection.

  8. Enhancing community detection by using local structural information

    NASA Astrophysics Data System (ADS)

    Xiang, Ju; Hu, Ke; Zhang, Yan; Bao, Mei-Hua; Tang, Liang; Tang, Yan-Ni; Gao, Yuan-Yuan; Li, Jian-Ming; Chen, Benyan; Hu, Jing-Bo

    2016-03-01

    Many real-world networks, such as gene networks, protein-protein interaction networks and metabolic networks, exhibit community structures, meaning the existence of groups of densely connected vertices in the networks. Many local similarity measures in the networks are closely related to the concept of the community structures, and may have a positive effect on community detection in the networks. Here, various local similarity measures are used to extract local structural information, which is then applied to community detection in the networks by using the edge-reweighting strategy. The effect of the local similarity measures on community detection is carefully investigated and compared in various networks. The experimental results show that the local similarity measures are crucial for the improvement of community detection methods, while the positive effect of the local similarity measures is closely related to the networks under study and applied community detection methods.

  9. Top-down and bottom-up regulation of macroalgal community structure on a Kenyan reef

    NASA Astrophysics Data System (ADS)

    Mörk, Erik; Sjöö, Gustaf Lilliesköld; Kautsky, Nils; McClanahan, Tim R.

    2009-09-01

    Top-down and bottom-up regulation in the form of grazing by herbivores and nutrient availability are important factors governing macroalgal communities in the coral reef ecosystem. Today, anthropogenic activities, such as over-harvesting of herbivorous fish and sea urchins and increased nutrient loading, are altering the interaction of these two structuring forces. The present study was conducted in Kenya and investigates the relative importance of herbivory and nutrient loading on macroalgal community dynamics, by looking at alterations in macroalgal functional groups, species diversity ( H') and biomass within experimental quadrats. The experiment was conducted in situ for 42 days during the dry season. Cages excluding large herbivorous fish and sea urchins were used in the study and nutrient addition was conducted using coated, slow-release fertilizer (nitrogen and phosphorous) at a site where herbivory is generally low and nutrient levels are relatively high for the region. Nutrient addition increased tissue nutrient content in the algae, and fertilized quadrats had 24% higher species diversity. Herbivore exclusion resulted in a 77% increase in algal biomass, mainly attributable to a >1000% increase in corticated forms. These results are in accordance with similar studies in other regions, but are unique in that they indicate that, even when prevailing nutrient levels are relatively high and herbivore pressure is relatively low, continued anthropogenic disturbance results in further ecological responses and increased reef degradation.

  10. Coupling of Algal Biofuel Production with Wastewater

    PubMed Central

    Panwar, Amit; Bisht, Tara Singh; Tamta, Sushma

    2014-01-01

    Microalgae have gained enormous consideration from scientific community worldwide emerging as a viable feedstock for a renewable energy source virtually being carbon neutral, high lipid content, and comparatively more advantageous to other sources of biofuels. Although microalgae are seen as a valuable source in majority part of the world for production of biofuels and bioproducts, still they are unable to accomplish sustainable large-scale algal biofuel production. Wastewater has organic and inorganic supplements required for algal growth. The coupling of microalgae with wastewater is an effective way of waste remediation and a cost-effective microalgal biofuel production. In this review article, we will primarily discuss the possibilities and current scenario regarding coupling of microalgal cultivation with biofuel production emphasizing recent progress in this area. PMID:24982930

  11. Algal biofuels from wastewater treatment high rate algal ponds.

    PubMed

    Craggs, R J; Heubeck, S; Lundquist, T J; Benemann, J R

    2011-01-01

    This paper examines the potential of algae biofuel production in conjunction with wastewater treatment. Current technology for algal wastewater treatment uses facultative ponds, however, these ponds have low productivity (∼10 tonnes/ha.y), are not amenable to cultivating single algal species, require chemical flocculation or other expensive processes for algal harvest, and do not provide consistent nutrient removal. Shallow, paddlewheel-mixed high rate algal ponds (HRAPs) have much higher productivities (∼30 tonnes/ha.y) and promote bioflocculation settling which may provide low-cost algal harvest. Moreover, HRAP algae are carbon-limited and daytime addition of CO(2) has, under suitable climatic conditions, the potential to double production (to ∼60 tonnes/ha.y), improve bioflocculation algal harvest, and enhance wastewater nutrient removal. Algae biofuels (e.g. biogas, ethanol, biodiesel and crude bio-oil), could be produced from the algae harvested from wastewater HRAPs, The wastewater treatment function would cover the capital and operation costs of algal production, with biofuel and recovered nutrient fertilizer being by-products. Greenhouse gas abatement results from both the production of the biofuels and the savings in energy consumption compared to electromechanical treatment processes. However, to achieve these benefits, further research is required, particularly the large-scale demonstration of wastewater treatment HRAP algal production and harvest. PMID:21330711

  12. Defined spatial structure stabilizes a synthetic multispecies bacterial community

    PubMed Central

    Kim, Hyun Jung; Boedicker, James Q.; Choi, Jang Wook; Ismagilov, Rustem F.

    2008-01-01

    This paper shows that for microbial communities, “fences make good neighbors.” Communities of soil microorganisms perform critical functions: controlling climate, enhancing crop production, and remediation of environmental contamination. Microbial communities in the oral cavity and the gut are of high biomedical interest. Understanding and harnessing the function of these communities is difficult: artificial microbial communities in the laboratory become unstable because of “winner-takes-all” competition among species. We constructed a community of three different species of wild-type soil bacteria with syntrophic interactions using a microfluidic device to control spatial structure and chemical communication. We found that defined microscale spatial structure is both necessary and sufficient for the stable coexistence of interacting bacterial species in the synthetic community. A mathematical model describes how spatial structure can balance the competition and positive interactions within the community, even when the rates of production and consumption of nutrients by species are mismatched, by exploiting nonlinearities of these processes. These findings provide experimental and modeling evidence for a class of communities that require microscale spatial structure for stability, and these results predict that controlling spatial structure may enable harnessing the function of natural and synthetic multispecies communities in the laboratory. PMID:19011107

  13. Community Structural Instability, Anomie, Imitation and Adolescent Suicidal Behavior

    ERIC Educational Resources Information Center

    Thorlindsson, Thorolfur; Bernburg, Jon Gunnar

    2009-01-01

    The current study examines the contextual effects of community structural characteristics, as well as the mediating role of key social mechanisms, on youth suicidal behavior in Iceland. We argue that the contextual influence of community structural instability on youth suicidal behavior should be mediated by weak attachment to social norms and…

  14. Investigating Effects of Invasive Species on Plant Community Structure

    ERIC Educational Resources Information Center

    Franklin, Wilfred

    2008-01-01

    In this article, the author presents a field study project that explores factors influencing forest community structure and lifts the veil off of "plant blindness." This ecological study consists of three laboratories: (1) preliminary field trip to the study site; (2) plant survey; and (3) analyzing plant community structure with descriptive…

  15. Discordant coral-symbiont structuring: factors shaping geographical variation of Symbiodinium communities in a facultative zooxanthellate coral genus, Oculina

    NASA Astrophysics Data System (ADS)

    Leydet, Karine Posbic; Hellberg, Michael E.

    2016-06-01

    Understanding the factors that help shape the association between corals and their algal symbionts, zooxanthellae ( Symbiodinium), is necessary to better understand the functional diversity and acclimatization potential of the coral host. However, most studies focus on tropical zooxanthellate corals and their obligate algal symbionts, thus limiting our full comprehension of coral-algal symbiont associations. Here, we examine algal associations in a facultative zooxanthellate coral. We survey the Symbiodinium communities associated with Oculina corals in the western North Atlantic and the Mediterranean using one clade-level marker ( psbA coding region) and three fine-scale markers ( cp23S- rDNA, b7sym15 flanking region, and b2sym17). We ask whether Oculina spp. harbor geographically different Symbiodinium communities across their geographic range and, if so, whether the host's genetics or habitat differences are correlated with this geographical variation. We found that Oculina corals harbor different Symbiodinium communities across their geographical range. Of the habitat differences (including chlorophyll a concentration and depth), sea surface temperature is better correlated with this geographical variation than the host's genetics, a pattern most evident in the Mediterranean. Our results suggest that although facultative zooxanthellate corals may be less dependent on their algal partners compared to obligate zooxanthellate corals, the Symbiodinium communities that they harbor may nevertheless reflect acclimatization to environmental variation among habitats.

  16. The structure and evolution of plankton communities

    NASA Astrophysics Data System (ADS)

    Longhurst, Alan R.

    New understanding of the circulation of ancient oceans is not yet matched by progress in our understanding of their pelagic ecology, though it was the planktonic ecosystems that generated our offshore oil and gas reserves. Can we assume that present-day models of ecosystem function are also valid for ancient seas? This question is addressed by a study of over 4000 plankton samples to derive a comprehensive, global description of zooplankton community structure in modern oceans: this shows that copepods form only 50% of the biomass of all plankton, ranging from 70% in polar to 35% in tropical seas. Comparable figures are derived from 14 other taxonomic categories of zooplankton. For trophic groupings, the data indicate globally: geletinous predators - 14%; gelatinous herbivores - 4%; raptorial predators - 33%; macrofiltering herbivores - 20%; macrofiltering omnivores - 25%; and detritivores - 3%. A simple, idealized model for the modern pelagic ecosystem is derived from these percentages which indicates that metazooplankton are not the most important consumers of pico- and nano-plankton production which itself probably constitutes 90% of primary production in warm oceans. This model is then compared with candidate life-forms available in Palaeozoic and Mesozoic oceans to determine to what extent it is also valid for ancient ecosystems: it is concluded that it is probably unnecessary to postulate models fundamentally differing from it in order to accommodate the life-forms, both protozoic and metazoic, known to have populated ancient seas. Remarkably few life-forms have existed which cannot be paralleled in the modern ocean, which contains remarkably few life-forms which cannot be paralleled in the Palaeozoic ocean. As a first assumption, then, it is reasonable to assume that energy pathways were similar in ancient oceans to those we study today.

  17. Identifying nutrient reference sites in nutrient-enriched regions-Using algal, invertebrate, and fish-community measures to identify stressor-breakpoint thresholds in Indiana rivers and streams, 2005-9

    USGS Publications Warehouse

    Caskey, Brian J.; Bunch, Aubrey R.; Shoda, Megan E.; Frey, Jeffrey W.; Selvaratnam, Shivi; Miltner, Robert J.

    2013-01-01

    Excess nutrients in aquatic ecosystems can lead to shifts in species composition, reduced dissolved oxygen concentrations, fish kills, and toxic algal blooms. In this study, nutrients, periphyton chlorophyll a (CHLa), and invertebrate- and fishcommunity data collected during 2005-9 were analyzed from 318 sites on Indiana rivers and streams. The objective of this study was to determine which invertebrate and fish-taxa attributes best reflect the conditions of streams in Indiana along a gradient of nutrient concentrations by (1) determining statistically and ecologically significant relations among the stressor (total nitrogen, total phosphorus, and periphyton CHLa) and response (invertebrate and fish community) variables; and (2) determining the levels at which invertebrate- and fish-community measures change in response to nutrients or periphyton CHLa. For water samples at the headwater sites, total nitrogen (TN) concentrations ranged from 0.343 to 21.6 milligrams per liter (mg/L) (median 2.12 mg/L), total phosphorus (TP) concentrations ranged from 0.050 to 1.44 mg/L (median 0.093 mg/L), and periphyton CHLa ranged from 0.947 to 629 mg/L (median 69.7 mg/L). At the wadable sites, TN concentrations ranged from 0.340 to 10.0 mg/L (median 2.31 mg/L), TP concentrations ranged from 0.050 to 1.24 mg/L (median 0.110 mg/L), and periphyton CHLa ranged from 0.383 to 719 mg/L (median 44.7 mg/L). Recursive partitioning identified statistically significant low and high breakpoint thresholds on invertebrate and fish measures, which demonstrated the ecological response in enriched conditions. The combined community (invertebrate and fish) mean low and high TN breakpoint thresholds were 1.03 and 2.61 mg/L, respectively. The mean low and high breakpoint thresholds for TP were 0.083 and 0.144 mg/L, respectively. The mean low and high breakpoint thresholds for periphyton CHLa were 20.9 and 98.6 milligrams per square meter (mg/m2), respectively. Additive quantile regression analysis

  18. Community structure of foraminiferal communities within temporal biozones from the western Arctic Ocean

    USGS Publications Warehouse

    Hayek, Lee-Ann C.; Buzas, Martin A.; Osterman, Lisa A.

    2007-01-01

    Community structure is often an overlooked dimension of biodiversity. Knowledge of community structure, the statistical distribution of the relative species abundance vector, makes possible comparisons and contrasts across time, space, and/or environmental conditions. Our results indicate that species of Arctic foraminifera in age-correlated cores from abyssal depths are each best described by log-series distributions. Using this structural information, we were able to determine that structural stability exists for at least 50 ka. The foraminiferal communities in this study show remarkable concordance, distributional similarity and support the neutral theory of biodiversity.

  19. Detecting Community Structure by Using a Constrained Label Propagation Algorithm

    PubMed Central

    Ratnavelu, Kuru

    2016-01-01

    Community structure is considered one of the most interesting features in complex networks. Many real-world complex systems exhibit community structure, where individuals with similar properties form a community. The identification of communities in a network is important for understanding the structure of said network, in a specific perspective. Thus, community detection in complex networks gained immense interest over the last decade. A lot of community detection methods were proposed, and one of them is the label propagation algorithm (LPA). The simplicity and time efficiency of the LPA make it a popular community detection method. However, the LPA suffers from instability detection due to randomness that is induced in the algorithm. The focus of this paper is to improve the stability and accuracy of the LPA, while retaining its simplicity. Our proposed algorithm will first detect the main communities in a network by using the number of mutual neighbouring nodes. Subsequently, nodes are added into communities by using a constrained LPA. Those constraints are then gradually relaxed until all nodes are assigned into groups. In order to refine the quality of the detected communities, nodes in communities can be switched to another community or removed from their current communities at various stages of the algorithm. We evaluated our algorithm on three types of benchmark networks, namely the Lancichinetti-Fortunato-Radicchi (LFR), Relaxed Caveman (RC) and Girvan-Newman (GN) benchmarks. We also apply the present algorithm to some real-world networks of various sizes. The current results show some promising potential, of the proposed algorithm, in terms of detecting communities accurately. Furthermore, our constrained LPA has a robustness and stability that are significantly better than the simple LPA as it is able to yield deterministic results. PMID:27176470

  20. Detecting Community Structure by Using a Constrained Label Propagation Algorithm.

    PubMed

    Chin, Jia Hou; Ratnavelu, Kuru

    2016-01-01

    Community structure is considered one of the most interesting features in complex networks. Many real-world complex systems exhibit community structure, where individuals with similar properties form a community. The identification of communities in a network is important for understanding the structure of said network, in a specific perspective. Thus, community detection in complex networks gained immense interest over the last decade. A lot of community detection methods were proposed, and one of them is the label propagation algorithm (LPA). The simplicity and time efficiency of the LPA make it a popular community detection method. However, the LPA suffers from instability detection due to randomness that is induced in the algorithm. The focus of this paper is to improve the stability and accuracy of the LPA, while retaining its simplicity. Our proposed algorithm will first detect the main communities in a network by using the number of mutual neighbouring nodes. Subsequently, nodes are added into communities by using a constrained LPA. Those constraints are then gradually relaxed until all nodes are assigned into groups. In order to refine the quality of the detected communities, nodes in communities can be switched to another community or removed from their current communities at various stages of the algorithm. We evaluated our algorithm on three types of benchmark networks, namely the Lancichinetti-Fortunato-Radicchi (LFR), Relaxed Caveman (RC) and Girvan-Newman (GN) benchmarks. We also apply the present algorithm to some real-world networks of various sizes. The current results show some promising potential, of the proposed algorithm, in terms of detecting communities accurately. Furthermore, our constrained LPA has a robustness and stability that are significantly better than the simple LPA as it is able to yield deterministic results. PMID:27176470

  1. What Community College Students Value: Delineating a Normative Structure for Community College Students

    ERIC Educational Resources Information Center

    Akin, Renea; Park, Toby J.

    2016-01-01

    This manuscript delineates a normative structure for community college students, outlines how this structure varies by student characteristics, and compares this structure to that of a previously established normative structure identified at a 4-year institution. A total of 512 student survey responses on the College Student Behaviors Inventory…

  2. A Stochastic Model for Detecting Overlapping and Hierarchical Community Structure

    PubMed Central

    Cao, Xiaochun; Wang, Xiao; Jin, Di; Guo, Xiaojie; Tang, Xianchao

    2015-01-01

    Community detection is a fundamental problem in the analysis of complex networks. Recently, many researchers have concentrated on the detection of overlapping communities, where a vertex may belong to more than one community. However, most current methods require the number (or the size) of the communities as a priori information, which is usually unavailable in real-world networks. Thus, a practical algorithm should not only find the overlapping community structure, but also automatically determine the number of communities. Furthermore, it is preferable if this method is able to reveal the hierarchical structure of networks as well. In this work, we firstly propose a generative model that employs a nonnegative matrix factorization (NMF) formulization with a l2,1 norm regularization term, balanced by a resolution parameter. The NMF has the nature that provides overlapping community structure by assigning soft membership variables to each vertex; the l2,1 regularization term is a technique of group sparsity which can automatically determine the number of communities by penalizing too many nonempty communities; and hence the resolution parameter enables us to explore the hierarchical structure of networks. Thereafter, we derive the multiplicative update rule to learn the model parameters, and offer the proof of its correctness. Finally, we test our approach on a variety of synthetic and real-world networks, and compare it with some state-of-the-art algorithms. The results validate the superior performance of our new method. PMID:25822148

  3. A stochastic model for detecting overlapping and hierarchical community structure.

    PubMed

    Cao, Xiaochun; Wang, Xiao; Jin, Di; Guo, Xiaojie; Tang, Xianchao

    2015-01-01

    Community detection is a fundamental problem in the analysis of complex networks. Recently, many researchers have concentrated on the detection of overlapping communities, where a vertex may belong to more than one community. However, most current methods require the number (or the size) of the communities as a priori information, which is usually unavailable in real-world networks. Thus, a practical algorithm should not only find the overlapping community structure, but also automatically determine the number of communities. Furthermore, it is preferable if this method is able to reveal the hierarchical structure of networks as well. In this work, we firstly propose a generative model that employs a nonnegative matrix factorization (NMF) formulization with a l(2,1) norm regularization term, balanced by a resolution parameter. The NMF has the nature that provides overlapping community structure by assigning soft membership variables to each vertex; the l(2,1) regularization term is a technique of group sparsity which can automatically determine the number of communities by penalizing too many nonempty communities; and hence the resolution parameter enables us to explore the hierarchical structure of networks. Thereafter, we derive the multiplicative update rule to learn the model parameters, and offer the proof of its correctness. Finally, we test our approach on a variety of synthetic and real-world networks, and compare it with some state-of-the-art algorithms. The results validate the superior performance of our new method. PMID:25822148

  4. Generic criticality of community structure in random graphs

    NASA Astrophysics Data System (ADS)

    Lipowski, Adam; Lipowska, Dorota

    2014-09-01

    We examine a community structure in random graphs of size n and link probability p /n determined with the Newman greedy optimization of modularity. Calculations show that for p <1 communities are nearly identical with clusters. For p =1 the average sizes of a community sav and of the giant community sg show a power-law increase sav˜nα' and sg˜nα. From numerical results we estimate α'≈0.26(1) and α ≈0.50(1) and using the probability distribution of sizes of communities we suggest that α'=α/2 should hold. For p >1 the community structure remains critical: (i) sav and sg have a power-law increase with α'≈α<1 and (ii) the probability distribution of sizes of communities is very broad and nearly flat for all sizes up to sg. For large p the modularity Q decays as Q˜p-0.55, which is intermediate between some previous estimations. To check the validity of the results, we also determine the community structure using another method, namely, a nongreedy optimization of modularity. Tests with some benchmark networks show that the method outperforms the greedy version. For random graphs, however, the characteristics of the community structure determined using both greedy and nongreedy optimizations are, within small statistical fluctuations, the same.

  5. Multiple simultaneous detection of Harmful Algal Blooms (HABs) through a high throughput bead array technology, with potential use in phytoplankton community analysis

    PubMed Central

    Scorzetti, G.; Brand, L.E.; Hitchcock, G.L.; Rein, K.S.; Sinigalliano, C.D.; Fell, J.W.

    2008-01-01

    As an alternative to traditional, morphology-based methods, molecular techniques can provide detection of multiple species within the HAB community and, more widely, the phytoplankton community in a rapid, accurate and simultaneous qualitative analysis. These methods require detailed knowledge of the molecular diversity within taxa in order to design efficient specific primers and specific probes able to avoid cross-reaction with non-target sequences. Isolates from Florida coastal communities were sequence-analyzed and compared with the GenBank database. Almost 44% of the genotypes obtained did not match any sequence in GenBank, showing the existence of a large and still unexplored biodiversity among taxa. Based on these results and on the GenBank database, we designed 14 species-specific probes and 4 sets of specific primers. Multiple simultaneous detection was achieved with a bead array method based on the use of a flow cytometer and color-coded microspheres, which are conjugated to the developed probes. Following a parallel double PCR amplification, which employed universal primers in a singleplex reaction and a set of species-specific primers in multiplex, detection was performed in a cost effective and highly specific analysis. This multi-format assay, which required less than 4 h to complete from sample collection, can be expanded according to need. Up to 100 different species can be identified simultaneously in a single sample, which allows for additional use of this method in community analyses extended to all phytoplankton species. Our initial field trials, which were based on the 14 species-specific probes, showed the co-existence and dominance of two or more species of Karenia during toxic blooms in Florida waters. PMID:20046212

  6. Virality Prediction and Community Structure in Social Networks

    NASA Astrophysics Data System (ADS)

    Weng, Lilian; Menczer, Filippo; Ahn, Yong-Yeol

    2013-08-01

    How does network structure affect diffusion? Recent studies suggest that the answer depends on the type of contagion. Complex contagions, unlike infectious diseases (simple contagions), are affected by social reinforcement and homophily. Hence, the spread within highly clustered communities is enhanced, while diffusion across communities is hampered. A common hypothesis is that memes and behaviors are complex contagions. We show that, while most memes indeed spread like complex contagions, a few viral memes spread across many communities, like diseases. We demonstrate that the future popularity of a meme can be predicted by quantifying its early spreading pattern in terms of community concentration. The more communities a meme permeates, the more viral it is. We present a practical method to translate data about community structure into predictive knowledge about what information will spread widely. This connection contributes to our understanding in computational social science, social media analytics, and marketing applications.

  7. Community structure in traffic zones based on travel demand

    NASA Astrophysics Data System (ADS)

    Sun, Li; Ling, Ximan; He, Kun; Tan, Qian

    2016-09-01

    Large structure in complex networks can be studied by dividing it into communities or modules. Urban traffic system is one of the most critical infrastructures. It can be abstracted into a complex network composed of tightly connected groups. Here, we analyze community structure in urban traffic zones based on the community detection method in network science. Spectral algorithm using the eigenvectors of matrices is employed. Our empirical results indicate that the traffic communities are variant with the travel demand distribution, since in the morning the majority of the passengers are traveling from home to work and in the evening they are traveling a contrary direction. Meanwhile, the origin-destination pairs with large number of trips play a significant role in urban traffic network's community division. The layout of traffic community in a city also depends on the residents' trajectories.

  8. Virality prediction and community structure in social networks.

    PubMed

    Weng, Lilian; Menczer, Filippo; Ahn, Yong-Yeol

    2013-01-01

    How does network structure affect diffusion? Recent studies suggest that the answer depends on the type of contagion. Complex contagions, unlike infectious diseases (simple contagions), are affected by social reinforcement and homophily. Hence, the spread within highly clustered communities is enhanced, while diffusion across communities is hampered. A common hypothesis is that memes and behaviors are complex contagions. We show that, while most memes indeed spread like complex contagions, a few viral memes spread across many communities, like diseases. We demonstrate that the future popularity of a meme can be predicted by quantifying its early spreading pattern in terms of community concentration. The more communities a meme permeates, the more viral it is. We present a practical method to translate data about community structure into predictive knowledge about what information will spread widely. This connection contributes to our understanding in computational social science, social media analytics, and marketing applications. PMID:23982106

  9. Algal functional annotation tool

    SciTech Connect

    Lopez, D.; Casero, D.; Cokus, S. J.; Merchant, S. S.; Pellegrini, M.

    2012-07-01

    The Algal Functional Annotation Tool is a web-based comprehensive analysis suite integrating annotation data from several pathway, ontology, and protein family databases. The current version provides annotation for the model alga Chlamydomonas reinhardtii, and in the future will include additional genomes. The site allows users to interpret large gene lists by identifying associated functional terms, and their enrichment. Additionally, expression data for several experimental conditions were compiled and analyzed to provide an expression-based enrichment search. A tool to search for functionally-related genes based on gene expression across these conditions is also provided. Other features include dynamic visualization of genes on KEGG pathway maps and batch gene identifier conversion.

  10. Faculty Scholarship at Community Colleges: Culture, Institutional Structures, and Socialization

    ERIC Educational Resources Information Center

    Morest, Vanessa Smith

    2015-01-01

    This chapter looks at community college faculty engagement in scholarship. Community college faculty spend the majority of their time engaged in teaching, and therefore their scholarship typically focuses on strengthening curriculum and instruction. The paper identifies some of the structural and cultural challenges and supports to scholarship at…

  11. Community Racial Segregation, Electoral Structure, and Minority Representation.

    ERIC Educational Resources Information Center

    Vedlitz, Arnold; Johnson, Charles A.

    1982-01-01

    Community electoral structures and segregation levels affect minority representation. Single-member district electorate systems provide significantly more favorable minority representation levels in segregated communities. In nonsegregated cities type of election system makes little difference in the equality of minority representation. (Author/AM)

  12. Exploratory Visualization of Graphs Based on Community Structure

    ERIC Educational Resources Information Center

    Liu, Yujie

    2013-01-01

    Communities, also called clusters or modules, are groups of nodes which probably share common properties and/or play similar roles within a graph. They widely exist in real networks such as biological, social, and information networks. Allowing users to interactively browse and explore the community structure, which is essential for understanding…

  13. Factors Affecting Soil Microbial Community Structure in Tomato Cropping Systems

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil and rhizosphere microbial communities in agroecosystems may be affected by soil, climate, plant species, and management. We identified some of the most important factors controlling microbial biomass and community structure in an agroecosystem utilizing tomato plants with the following nine tre...

  14. Algal Biofuels; Algal Biofuels R&D at NREL (Brochure)

    SciTech Connect

    Not Available

    2010-09-01

    An overview of NREL's algal biofuels projects, including U.S. Department of Energy-funded work, projects with U.S. and international partners, and Laboratory Directed Research and Development projects.

  15. Harmful Algal Blooms and Drinking Water Treatment Research

    EPA Science Inventory

    EPA has been conducting algal bloom research at multiple facilities around Lake Erie over the past few years to help communities confront the challenge of keeping cyanobacterial toxins from reaching consumers’ taps, while minimizing the financial burden. The first goal of this re...

  16. Artificial neural networks and ecological communities (Book Review: Modelling community structure in freshwater ecosystems)

    USGS Publications Warehouse

    DeAngelis, Donald L.

    2005-01-01

    Review info: Modeling community structure in freshwater ecosystems. Edited by Sovan Lek, Michele Scardi, Piet F.M. Verdonschot, Jean-Pierre Descy, and Young-Seuk Park, 2005. ISBN: 3-540-23940-5, 518 pp.

  17. Synergistic effects of algal overgrowth and corallivory on Caribbean reef-building corals.

    PubMed

    Wolf, Alexander T; Nugues, Maggy M

    2013-08-01

    Indirect biotic interactions play a crucial role in structuring ecological communities, but many of these interactions have not been explored. Algal competition and corallivory are two major stressors contributing to the decline of coral reefs. Here, we provide the first evidence of algal-induced corallivory and synergistic effects between the two stressors on corals. When corals (Montastraeafaveolata) were placed in contact with algae (Halimeda opuntia) together with corallivorous fireworms (Hermodice carunculata) in aquaria, corals suffered high tissue mortality. This mortality was reduced in the presence of algae only, and no mortality occurred in the presence of fireworms only or when excluding both algae and fireworms. These findings were supported by field observations showing a predominance of fireworms inside algae contacting live corals, and by an in situ experiment demonstrating higher coral mortality in contact with algae left undisturbed than with algae from which all mobile epifauna were periodically removed. Among the main contributing mechanisms, we suggest that algal contact produces decaying coral tissue that attracts the corallivore and enhances its aggregation behavior. Our study demonstrates an indirect effect pathway by which algae can impact corals, which shares similarities with the classic models of apparent competition and habitat facilitation. PMID:24015510

  18. Edge ratio and community structure in networks

    NASA Astrophysics Data System (ADS)

    Cafieri, Sonia; Hansen, Pierre; Liberti, Leo

    2010-02-01

    A hierarchical divisive algorithm is proposed for identifying communities in complex networks. To that effect, the definition of community in the weak sense of Radicchi [Proc. Natl. Acad. Sci. U.S.A. 101, 2658 (2004)] is extended into a criterion for a bipartition to be optimal: one seeks to maximize the minimum for both classes of the bipartition of the ratio of inner edges to cut edges. A mathematical program is used within a dichotomous search to do this in an optimal way for each bipartition. This includes an exact solution of the problem of detecting indivisible communities. The resulting hierarchical divisive algorithm is compared with exact modularity maximization on both artificial and real world data sets. For two problems of the former kind optimal solutions are found; for five problems of the latter kind the edge ratio algorithm always appears to be competitive. Moreover, it provides additional information in several cases, notably through the use of the dendrogram summarizing the resolution. Finally, both algorithms are compared on reduced versions of the data sets of Girvan and Newman [Proc. Natl. Acad. Sci. U.S.A. 99, 7821 (2002)] and of Lancichinetti [Phys. Rev. E 78, 046110 (2008)]. Results for these instances appear to be comparable.

  19. Growing network model for community with group structure

    NASA Astrophysics Data System (ADS)

    Noh, Jae Dong; Jeong, Hyeong-Chai; Ahn, Yong-Yeol; Jeong, Hawoong

    2005-03-01

    We propose a growing network model for a community with a group structure. The community consists of individual members and groups, gatherings of members. The community grows as a new member is introduced by an existing member at each time step. The new member then creates a new group or joins one of the groups of the introducer. We investigate the emerging community structure analytically and numerically. The group size distribution shows a power-law distribution for a variety of growth rules, while the activity distribution follows an exponential or a power law depending on the details of the growth rule. We also present an analysis of empirical data from online communities the “Groups” in http://www.yahoo.com and the “Cafe” in http://www.daum.net, which show a power-law distribution for a wide range of group sizes.

  20. Community structure of a microbial mat: the phylogenetic dimension.

    PubMed Central

    Risatti, J B; Capman, W C; Stahl, D A

    1994-01-01

    Traditional studies of microbial communities are incomplete because of the inability to identify and quantify all contributing populations. In the present study, we directly determine the abundance and distribution of sulfate-reducing bacterial populations in a microbial mat community by using hybridization probes complementary to the 16S-like rRNAs of major phylogenetic groups. Most of the major groups were found in this single community, distributed for the most part in nonoverlapping depth intervals of the mat. The reflection of the phylogenetic structure in the community structure suggests that those species making up the major phylogenetic groups perform specific interrelated metabolic functions in the community. Comparison of population profiles to previously observed rates of sulfate reduction suggests there are additional populations of sulfate-reducing bacteria both within the photooxic zone and deeper in the mat. Images PMID:7937858

  1. Growing network model for community with group structure.

    PubMed

    Noh, Jae Dong; Jeong, Hyeong-Chai; Ahn, Yong-Yeol; Jeong, Hawoong

    2005-03-01

    We propose a growing network model for a community with a group structure. The community consists of individual members and groups, gatherings of members. The community grows as a new member is introduced by an existing member at each time step. The new member then creates a new group or joins one of the groups of the introducer. We investigate the emerging community structure analytically and numerically. The group size distribution shows a power-law distribution for a variety of growth rules, while the activity distribution follows an exponential or a power law depending on the details of the growth rule. We also present an analysis of empirical data from online communities the "Groups" in http://www.yahoo.com and the "Cafe" in http://www.daum.net, which show a power-law distribution for a wide range of group sizes. PMID:15903517

  2. Community structure of a microbial mat: The phylogenetic dimension

    USGS Publications Warehouse

    Risatti, J.B.; Capman, W.C.; Stahl, D.A.

    1994-01-01

    Traditional studies of microbial communities are incomplete because of the inability to identify and quantify all contributing populations. In the present study, we directly determine the abundance and distribution of sulfate-reducing bacterial populations in a microbial mat community by using hybridization probes complementary to the 16S-like rRNAs of major phylogenetic groups. Most of the major groups were found in this single community, distributed for the most part in nonoverlapping depth intervals of the mat. The reflection of the phylogenetic structure in the community structure suggests that those species making up the major phylogenetic groups perform specific interrelated metabolic functions in the community. Comparison of population profiles to previously observed rates of sulfate reduction suggests there are additional populations of sulfate-reducing bacteria both within the photooxic zone and deeper in the mat.

  3. Method to find community structures based on information centrality

    NASA Astrophysics Data System (ADS)

    Fortunato, Santo; Latora, Vito; Marchiori, Massimo

    2004-11-01

    Community structures are an important feature of many social, biological, and technological networks. Here we study a variation on the method for detecting such communities proposed by Girvan and Newman and based on the idea of using centrality measures to define the community boundaries [M. Girvan and M. E. J. Newman, Proc. Natl. Acad. Sci. U.S.A. 99, 7821 (2002)]. We develop an algorithm of hierarchical clustering that consists in finding and removing iteratively the edge with the highest information centrality. We test the algorithm on computer generated and real-world networks whose community structure is already known or has been studied by means of other methods. We show that our algorithm, although it runs to completion in a time O(n4) , is very effective especially when the communities are very mixed and hardly detectable by the other methods.

  4. Community structure of a microbial mat: the phylogenetic dimension.

    PubMed

    Risatti, J B; Capman, W C; Stahl, D A

    1994-10-11

    Traditional studies of microbial communities are incomplete because of the inability to identify and quantify all contributing populations. In the present study, we directly determine the abundance and distribution of sulfate-reducing bacterial populations in a microbial mat community by using hybridization probes complementary to the 16S-like rRNAs of major phylogenetic groups. Most of the major groups were found in this single community, distributed for the most part in nonoverlapping depth intervals of the mat. The reflection of the phylogenetic structure in the community structure suggests that those species making up the major phylogenetic groups perform specific interrelated metabolic functions in the community. Comparison of population profiles to previously observed rates of sulfate reduction suggests there are additional populations of sulfate-reducing bacteria both within the photooxic zone and deeper in the mat. PMID:7937858

  5. Exploring community structure in networks by consensus dynamics

    NASA Astrophysics Data System (ADS)

    He, He; Yang, Bo; Hu, Xiaoming

    2016-05-01

    This paper investigates the relationship between community structure and consensus dynamics in complex networks. We analyze the dynamical process towards consensus and show that those sets of densely interconnected nodes corresponding to well-defined communities appear in different time scales. In order to reveal such topological scales, two algorithms built around the idea of visualizing the evolution of different measured quantities are proposed. Then we test our algorithms on a few benchmark graphs whose community structures are already known. Numeric simulations are given to demonstrate the effectiveness and reliability of our methods.

  6. Fragmentation alters stream fish community structure in dendritic ecological networks.

    PubMed

    Perkin, Joshuah S; Gido, Keith B

    2012-12-01

    Effects of fragmentation on the ecology of organisms occupying dendritic ecological networks (DENs) have recently been described through both conceptual and mathematical models, but few hypotheses have been tested in complex, real-world ecosystems. Stream fishes provide a model system for assessing effects of fragmentation on the structure of communities occurring within DENs, including how fragmentation alters metacommunity dynamics and biodiversity. A recently developed habitat-availability measure, the "dendritic connectivity index" (DCI), allows for assigning quantitative measures of connectivity in DENs regardless of network extent or complexity, and might be used to predict fish community response to fragmentation. We characterized stream fish community structure in 12 DENs in the Great Plains, USA, during periods of dynamic (summer) and muted (fall) discharge regimes to test the DCI as a predictive model of fish community response to fragmentation imposed by road crossings. Results indicated that fish communities in stream segments isolated by road crossings had reduced species richness (alpha diversity) relative to communities that maintained connectivity with the surrounding DEN during summer and fall. Furthermore, isolated communities had greater dissimilarity (beta diversity) to downstream sites notisolated by road crossings during summer and fall. Finally, dissimilarity among communities within DENs decreased as a function of increased habitat connectivity (measured using the DCI) for summer and fall, suggesting that communities within highly connected DENs tend to be more homogeneous. Our results indicate that the DCI is sensitive to community effects of fragmentation in riverscapes and might be used by managers to predict ecological responses to changes in habitat connectivity. Moreover, our findings illustrate that relating structural connectivity of riverscapes to functional connectivity among communities might aid in maintaining metacommunity

  7. Algal taxonomy: a road to nowhere?

    PubMed

    De Clerck, Olivier; Guiry, Michael D; Leliaert, Frederik; Samyn, Yves; Verbruggen, Heroen

    2013-04-01

    The widespread view of taxonomy as an essentially retrogressive and outmoded science unable to cope with the current biodiversity crisis stimulated us to analyze the current status of cataloguing global algal diversity. Contrary to this largely pessimistic belief, species description rates of algae through time and trends in the number of active taxonomists, as revealed by the web resource AlgaeBase, show a much more positive picture. More species than ever before are being described by a large community of algal taxonomists. The lack of any decline in the rate at which new species and genera are described, however, is indicative of the large proportion of undiscovered diversity and bears heavily on any prediction of global algal species diversity and the time needed to catalogue it. The saturation of accumulation curves of higher taxa (family, order, and classes) on the other hand suggest that at these taxonomic levels most diversity has been discovered. This reasonably positive picture does not imply that algal taxonomy does not face serious challenges in the near future. The observed levels of cryptic diversity in algae, combined with the shift in methods used to characterize them, have resulted in a rampant uncertainty about the status of many older species. As a consequence, there is a tendency in phycology to move gradually away from traditional names to a more informal system whereby clade-, specimen- or strain-based identifiers are used to communicate biological information. Whether these informal names for species-level clades represent a temporary situation stimulated by the lag between species discovery and formal description, or an incipient alternative or parallel taxonomy, will be largely determined by how well we manage to integrate historical collections into modern taxonomic research. Additionally, there is a pressing need for a consensus about the organizational framework to manage the information about algal species names. An eventual strategy

  8. Distributed network management in the flat structured mobile communities

    NASA Astrophysics Data System (ADS)

    Balandina, Elena

    2005-10-01

    Delivering proper management into the flat structured mobile communities is crucial for improving users experience and increase applications diversity in mobile networks. The available P2P applications do application-centric management, but it cannot replace network-wide management, especially when a number of different applications are used simultaneously in the network. The network-wide management is the key element required for a smooth transition from standalone P2P applications to the self-organizing mobile communities that maintain various services with quality and security guaranties. The classical centralized network management solutions are not applicable in the flat structured mobile communities due to the decentralized nature and high mobility of the underlying networks. Also the basic network management tasks have to be revised taking into account specialties of the flat structured mobile communities. The network performance management becomes more dependent on the current nodes' context, which also requires extension of the configuration management functionality. The fault management has to take into account high mobility of the network nodes. The performance and accounting managements are mainly targeted in maintain an efficient and fair access to the resources within the community, however they also allow unbalanced resource use of the nodes that explicitly permit it, e.g. as a voluntary donation to the community or due to the profession (commercial) reasons. The security management must implement the new trust models, which are based on the community feedback, professional authorization, and a mix of both. For fulfilling these and another specialties of the flat structured mobile communities, a new network management solution is demanded. The paper presents a distributed network management solution for flat structured mobile communities. Also the paper points out possible network management roles for the different parties (e.g. operators, service

  9. Fueling Future with Algal Genomics

    SciTech Connect

    Grigoriev, Igor

    2012-07-05

    Algae constitute a major component of fundamental eukaryotic diversity, play profound roles in the carbon cycle, and are prominent candidates for biofuel production. The US Department of Energy Joint Genome Institute (JGI) is leading the world in algal genome sequencing (http://jgi.doe.gov/Algae) and contributes of the algal genome projects worldwide (GOLD database, 2012). The sequenced algal genomes offer catalogs of genes, networks, and pathways. The sequenced first of its kind genomes of a haptophyte E.huxleyii, chlorarachniophyte B.natans, and cryptophyte G.theta fill the gaps in the eukaryotic tree of life and carry unique genes and pathways as well as molecular fossils of secondary endosymbiosis. Natural adaptation to conditions critical for industrial production is encoded in algal genomes, for example, growth of A.anophagefferens at very high cell densities during the harmful algae blooms or a global distribution across diverse environments of E.huxleyii, able to live on sparse nutrients due to its expanded pan-genome. Communications and signaling pathways can be derived from simple symbiotic systems like lichens or complex marine algae metagenomes. Collectively these datasets derived from algal genomics contribute to building a comprehensive parts list essential for algal biofuel development.

  10. Wave stress and coral community structure in Hawaii

    NASA Astrophysics Data System (ADS)

    Dollar, S. J.

    1982-10-01

    The most significant factor determining the structure of Hawaiian reef coral communities is physical disturbance from waves. Sequential analysis of community structure off the west coast of the island of Hawaii shows that variation of wave energy and storm frequency clearly affects organization in time and space. Normal conditions of low wave stress maintain four well-defined reef zones; diversity is highest at intermediate depths and decreases in physically rigorous shallow areas and stable deep reef slopes. Intermediate level storm wave events cause variable effects within the reef zones, but the zonation pattern, as a whole, is maintained. Diversity increases in zones that are dominated by a single species largely through nonlethal fragmentation and transport, but decreases in the zone of most equitable species distribution. Conversely, severe infrequent storm disturbances that cause massive mortality to all coral species wipe out the pattern of community structure and return the entire community to a low diversity early successional stage.

  11. Jellyfish modulate bacterial dynamic and community structure.

    PubMed

    Tinta, Tinkara; Kogovšek, Tjaša; Malej, Alenka; Turk, Valentina

    2012-01-01

    Jellyfish blooms have increased in coastal areas around the world and the outbreaks have become longer and more frequent over the past few decades. The Mediterranean Sea is among the heavily affected regions and the common bloom-forming taxa are scyphozoans Aurelia aurita s.l., Pelagia noctiluca, and Rhizostoma pulmo. Jellyfish have few natural predators, therefore their carcasses at the termination of a bloom represent an organic-rich substrate that supports rapid bacterial growth, and may have a large impact on the surrounding environment. The focus of this study was to explore whether jellyfish substrate have an impact on bacterial community phylotype selection. We conducted in situ jellyfish-enrichment experiment with three different jellyfish species. Bacterial dynamic together with nutrients were monitored to assess decaying jellyfish-bacteria dynamics. Our results show that jellyfish biomass is characterized by protein rich organic matter, which is highly bioavailable to 'jellyfish-associated' and 'free-living' bacteria, and triggers rapid shifts in bacterial population dynamics and composition. Based on 16S rRNA clone libraries and denaturing gradient gel electrophoresis (DGGE) analysis, we observed a rapid shift in community composition from unculturable Alphaproteobacteria to culturable species of Gammaproteobacteria and Flavobacteria. The results of sequence analyses of bacterial isolates and of total bacterial community determined by culture independent genetic analysis showed the dominance of the Pseudoalteromonadaceae and the Vibrionaceae families. Elevated levels of dissolved proteins, dissolved organic and inorganic nutrient release, bacterial abundance and carbon production as well as ammonium concentrations characterized the degradation process. The biochemical composition of jellyfish species may influence changes in the amount of accumulated dissolved organic and inorganic nutrients. Our results can contribute insights into possible changes in

  12. Jellyfish Modulate Bacterial Dynamic and Community Structure

    PubMed Central

    Tinta, Tinkara; Kogovšek, Tjaša; Malej, Alenka; Turk, Valentina

    2012-01-01

    Jellyfish blooms have increased in coastal areas around the world and the outbreaks have become longer and more frequent over the past few decades. The Mediterranean Sea is among the heavily affected regions and the common bloom - forming taxa are scyphozoans Aurelia aurita s.l., Pelagia noctiluca, and Rhizostoma pulmo. Jellyfish have few natural predators, therefore their carcasses at the termination of a bloom represent an organic-rich substrate that supports rapid bacterial growth, and may have a large impact on the surrounding environment. The focus of this study was to explore whether jellyfish substrate have an impact on bacterial community phylotype selection. We conducted in situ jellyfish - enrichment experiment with three different jellyfish species. Bacterial dynamic together with nutrients were monitored to assess decaying jellyfish-bacteria dynamics. Our results show that jellyfish biomass is characterized by protein rich organic matter, which is highly bioavailable to ‘jellyfish - associated’ and ‘free - living’ bacteria, and triggers rapid shifts in bacterial population dynamics and composition. Based on 16S rRNA clone libraries and denaturing gradient gel electrophoresis (DGGE) analysis, we observed a rapid shift in community composition from unculturable Alphaproteobacteria to culturable species of Gammaproteobacteria and Flavobacteria. The results of sequence analyses of bacterial isolates and of total bacterial community determined by culture independent genetic analysis showed the dominance of the Pseudoalteromonadaceae and the Vibrionaceae families. Elevated levels of dissolved proteins, dissolved organic and inorganic nutrient release, bacterial abundance and carbon production as well as ammonium concentrations characterized the degradation process. The biochemical composition of jellyfish species may influence changes in the amount of accumulated dissolved organic and inorganic nutrients. Our results can contribute insights into

  13. The social structure of microbial community involved in colonization resistance.

    PubMed

    He, Xuesong; McLean, Jeffrey S; Guo, Lihong; Lux, Renate; Shi, Wenyuan

    2014-03-01

    It is well established that host-associated microbial communities can interfere with the colonization and establishment of microbes of foreign origins, a phenomenon often referred to as bacterial interference or colonization resistance. However, due to the complexity of the indigenous microbiota, it has been extremely difficult to elucidate the community colonization resistance mechanisms and identify the bacterial species involved. In a recent study, we have established an in vitro mice oral microbial community (O-mix) and demonstrated its colonization resistance against an Escherichia coli strain of mice gut origin. In this study, we further analyzed the community structure of the O-mix by using a dilution/regrowth approach and identified the bacterial species involved in colonization resistance against E. coli. Our results revealed that, within the O-mix there were three different types of bacterial species forming unique social structure. They act as 'Sensor', 'Mediator' and 'Killer', respectively, and have coordinated roles in initiating the antagonistic action and preventing the integration of E. coli. The functional role of each identified bacterial species was further confirmed by E. coli-specific responsiveness of the synthetic communities composed of different combination of the identified players. The study reveals for the first time the sophisticated structural and functional organization of a colonization resistance pathway within a microbial community. Furthermore, our results emphasize the importance of 'Facilitation' or positive interactions in the development of community-level functions, such as colonization resistance. PMID:24088624

  14. Measuring the significance of community structure in complex networks

    NASA Astrophysics Data System (ADS)

    Hu, Yanqing; Nie, Yuchao; Yang, Hua; Cheng, Jie; Fan, Ying; di, Zengru

    2010-12-01

    Many complex systems can be represented as networks, and separating a network into communities could simplify functional analysis considerably. Many approaches have recently been proposed to detect communities, but a method to determine whether the detected communities are significant is still lacking. In this paper, an index to evaluate the significance of communities in networks is proposed based on perturbation of the network. In contrast to previous approaches, the network is disturbed gradually, and the index is defined by integrating all of the similarities between the community structures before and after perturbation. Moreover, by taking the null model into account, the index eliminates scale effects. Thus, it can evaluate and compare the significance of communities in different networks. The method has been tested in many artificial and real-world networks. The results show that the index is in fact independent of the size of the network and the number of communities. With this approach, clear communities are found to always exist in social networks, but significant communities cannot be found in protein interactions and metabolic networks.

  15. Towards developing algal synthetic biology.

    PubMed

    Scaife, Mark Aden; Smith, Alison Gail

    2016-06-15

    The genetic, physiological and metabolic diversity of microalgae has driven fundamental research into photosynthesis, flagella structure and function, and eukaryotic evolution. Within the last 10 years these organisms have also been investigated as potential biotechnology platforms, for example to produce high value compounds such as long chain polyunsaturated fatty acids, pigments and antioxidants, and for biodiesel precursors, in particular triacylglycerols (TAGs). Transformation protocols, molecular tools and genome sequences are available for a number of model species including the green alga Chlamydomonas reinhardtii and the diatom Phaeodactylum tricornutum, although for both species there are bottlenecks to be overcome to allow rapid and predictable genetic manipulation. One approach to do this would be to apply the principles of synthetic biology to microalgae, namely the cycle of Design-Build-Test, which requires more robust, predictable and high throughput methods. In this mini-review we highlight recent progress in the areas of improving transgene expression, genome editing, identification and design of standard genetic elements (parts), and the use of microfluidics to increase throughput. We suggest that combining these approaches will provide the means to establish algal synthetic biology, and that application of standard parts and workflows will avoid parallel development and capitalize on lessons learned from other systems. PMID:27284033

  16. Measuring the robustness of network community structure using assortativity

    PubMed Central

    Shizuka, Daizaburo; Farine, Damien R.

    2016-01-01

    The existence of discrete social clusters, or ‘communities’, is a common feature of social networks in human and nonhuman animals. The level of such community structure in networks is typically measured using an index of modularity, Q. While modularity quantifies the degree to which individuals associate within versus between social communities and provides a useful measure of structure in the social network, it assumes that the network has been well sampled. However, animal social network data is typically subject to sampling errors. In particular, the associations among individuals are often not sampled equally, and animal social network studies are often based on a relatively small set of observations. Here, we extend an existing framework for bootstrapping network metrics to provide a method for assessing the robustness of community assignment in social networks using a metric we call community assortativity (rcom). We use simulations to demonstrate that modularity can reliably detect the transition from random to structured associations in networks that differ in size and number of communities, while community assortativity accurately measures the level of confidence based on the detectability of associations. We then demonstrate the use of these metrics using three publicly available data sets of avian social networks. We suggest that by explicitly addressing the known limitations in sampling animal social network, this approach will facilitate more rigorous analyses of population-level structural patterns across social systems. PMID:26949266

  17. Active Women: Perspectives on Their Structural Position in the Community.

    ERIC Educational Resources Information Center

    Moyer, Harriett; And Others

    An exploratory pilot study to determine the personal characteristics of women community leaders and their position in the power structure was conducted in Chippewa and Eau Claire Counties, Wisconsin. The research design involved a comparison of three samples: the traditional power structure identified through reputational techniques; the active…

  18. Alternative community structures in a kelp-urchin community: A qualitative modeling approach

    USGS Publications Warehouse

    Montano-Moctezuma, G.; Li, H.W.; Rossignol, P.A.

    2007-01-01

    Shifts in interaction patterns within a community may result from periodic disturbances and climate. The question arises as to the extent and significance of these shifting patterns. Using a novel approach to link qualitative mathematical models and field data, namely using the inverse matrix to identify the community matrix, we reconstructed community networks from kelp forests off the Oregon Coast. We simulated all ecologically plausible interactions among community members, selected the models whose outcomes match field observations, and identified highly frequent links to characterize the community network from a particular site. We tested all possible biologically reasonable community networks through qualitative simulations, selected those that matched patterns observed in the field, and further reduced the set of possibilities by retaining those that were stable. We found that a community can be represented by a set of alternative structures, or scenarios. From 11,943,936 simulated models, 0.23% matched the field observations; moreover, only 0.006%, or 748 models, were highly reliable in their predictions and met conditions for stability. Predator-prey interactions as well as non-predatory relationships were consistently found in most of the 748 models. These highly frequent connections were useful to characterize the community network in the study site. We suggest that alternative networks provide the community with a buffer to disturbance, allowing it to continuously reorganize to adapt to a variable environment. This is possible due to the fluctuating capacities of foraging species to consume alternate resources. This suggestion is sustained by our results, which indicate that none of the models that matched field observations were fully connected. This plasticity may contribute to the persistence of these communities. We propose that qualitative simulations represent a powerful technique to raise new hypotheses concerning community dynamics and to

  19. Small herbivores suppress algal accumulation on Agatti atoll, Indian Ocean

    NASA Astrophysics Data System (ADS)

    Cernohorsky, Nicole H.; McClanahan, Timothy R.; Babu, Idrees; Horsák, Michal

    2015-12-01

    Despite large herbivorous fish being generally accepted as the main group responsible for preventing algal accumulation on coral reefs, few studies have experimentally examined the relative importance of herbivore size on algal communities. This study used exclusion cages with two different mesh sizes (1 × 1 cm and 6 × 6 cm) to investigate the impact of different-sized herbivores on algal accumulation rates on the shallow (<2 m) back-reef of Agatti atoll, Lakshadweep. The fine-mesh cages excluded all visible herbivores, which had rapid and lasting effects on the benthic communities, and, after 127 d of deployment, there was a visible and significant increase in algae (mainly macroalgae) with algal volume being 13 times greater than in adjacent open areas. The coarse-mesh cages excluded larger fishes (>8 cm body depth) while allowing smaller fishes to access the plots. In contrast to the conclusions of most previous studies, the exclusion of large herbivores had no significant effect on the accumulation of benthic algae and the amount of algae present within the coarse-mesh cages was relatively consistent throughout the experimental period (around 50 % coverage and 1-2 mm height). The difference in algal accumulation between the fine-mesh and coarse-mesh cages appears to be related to the actions of small individuals from 12 herbivorous fish species (0.17 ind. m-2 and 7.7 g m-2) that were able to enter through the coarse mesh. Although restricted to a single habitat, these results suggest that when present in sufficient densities and diversity, small herbivorous fishes can prevent the accumulation of algal biomass on coral reefs.

  20. Comprehensive spectral approach for community structure analysis on complex networks

    NASA Astrophysics Data System (ADS)

    Danila, Bogdan

    2016-02-01

    A simple but efficient spectral approach for analyzing the community structure of complex networks is introduced. It works the same way for all types of networks, by spectrally splitting the adjacency matrix into a "unipartite" and a "multipartite" component. These two matrices reveal the structure of the network from different perspectives and can be analyzed at different levels of detail. Their entries, or the entries of their lower-rank approximations, provide measures of the affinity or antagonism between the nodes that highlight the communities and the "gateway" links that connect them together. An algorithm is then proposed to achieve the automatic assignment of the nodes to communities based on the information provided by either matrix. This algorithm naturally generates overlapping communities but can also be tuned to eliminate the overlaps.

  1. Community structures and role detection in music networks

    NASA Astrophysics Data System (ADS)

    Teitelbaum, T.; Balenzuela, P.; Cano, P.; Buldú, Javier M.

    2008-12-01

    We analyze the existence of community structures in two different social networks using data obtained from similarity and collaborative features between musical artists. Our analysis reveals some characteristic organizational patterns and provides information about the driving forces behind the growth of the networks. In the similarity network, we find a strong correlation between clusters of artists and musical genres. On the other hand, the collaboration network shows two different kinds of communities: rather small structures related to music bands and geographic zones, and much bigger communities built upon collaborative clusters with a high number of participants related through the period the artists were active. Finally, we detect the leading artists inside their corresponding communities and analyze their roles in the network by looking at a few topological properties of the nodes.

  2. Community structures and role detection in music networks.

    PubMed

    Teitelbaum, T; Balenzuela, P; Cano, P; Buldú, Javier M

    2008-12-01

    We analyze the existence of community structures in two different social networks using data obtained from similarity and collaborative features between musical artists. Our analysis reveals some characteristic organizational patterns and provides information about the driving forces behind the growth of the networks. In the similarity network, we find a strong correlation between clusters of artists and musical genres. On the other hand, the collaboration network shows two different kinds of communities: rather small structures related to music bands and geographic zones, and much bigger communities built upon collaborative clusters with a high number of participants related through the period the artists were active. Finally, we detect the leading artists inside their corresponding communities and analyze their roles in the network by looking at a few topological properties of the nodes. PMID:19123615

  3. Parasitism, community structure and biodiversity in intertidal ecosystems.

    PubMed

    Mouritsen, K N; Poulin, R

    2002-01-01

    There is mounting evidence that parasites can influence the composition and structure of natural animal communities. In spite of this, it is difficult to assess just how important parasitism is for community structure because very few studies have been designed specifically to address the role of parasites at the community level, no doubt because it is difficult to manipulate the abundance of parasites in field experiments. Here, we bring together a large amount of published information on parasitism in intertidal communities to highlight the potential influence of parasites on the structure and biodiversity of these communities. We first review the impact of metazoan parasites on the survival, reproduction, growth and behaviour of intertidal invertebrates, from both rocky shores and soft-sediment flats. Published evidence suggests that the impact of parasites on individuals is often severe, though their effects at the population level are dependent on prevalence and intensity of infection. We then put this information together in a discussion of the impact of parasitism at the community level. We emphasize two ways in which parasites can modify the structure of intertidal communities. First, the direct impact of parasites on the abundance of key host species can decrease the importance of these hosts in competition or predator-prey interactions with other species. Second, the indirect effects of parasites on the behaviour of their hosts, e.g. burrowing ability or spatial distribution within the intertidal zone, can cause changes to various features of the habitat for other intertidal species, leading to their greater settlement success or to their local disappearance. Our synthesis allows specific predictions to be made regarding the potential impact of parasites in certain intertidal systems, and suggests that parasites must be included in future community studies and food web models of intertidal ecosystems. PMID:12396219

  4. Elevated Carbon Dioxide Alters the Structure of Soil Microbial Communities

    PubMed Central

    Deng, Ye; He, Zhili; Xu, Meiying; Qin, Yujia; Van Nostrand, Joy D.; Wu, Liyou; Roe, Bruce A.; Wiley, Graham; Hobbie, Sarah E.; Reich, Peter B.

    2012-01-01

    Pyrosequencing analysis of 16S rRNA genes was used to examine impacts of elevated CO2 (eCO2) on soil microbial communities from 12 replicates each from ambient CO2 (aCO2) and eCO2 settings. The results suggest that the soil microbial community composition and structure significantly altered under conditions of eCO2, which was closely associated with soil and plant properties. PMID:22307288

  5. Change in Fish Community Structure in the Barents Sea

    PubMed Central

    Aschan, Michaela; Fossheim, Maria; Greenacre, Michael; Primicerio, Raul

    2013-01-01

    Change in oceanographic conditions causes structural alterations in marine fish communities, but this effect may go undetected as most monitoring programs until recently mainly have focused on oceanography and commercial species rather than on whole ecosystems. In this paper, the objective is to describe the spatial and temporal changes in the Barents Sea fish community in the period 1992–2004 while taking into consideration the observed abundance and biodiversity patterns for all 82 observed fish species. We found that the spatial structure of the Barents Sea fish community was determined by abiotic factors such as temperature and depth. The observed species clustered into a deep assemblage, a warm water southern assemblage, both associated with Atlantic water, and a cold water north-eastern assemblage associated with mixed water. The latitude of the cold water NE and warm water S assemblages varied from year to year, but no obvious northward migration was observed over time. In the period 1996–1999 we observed a significant reduction in total fish biomass, abundance, mean fish weight, and a change in community structure including an increase in the pelagic/demersal ratio. This change in community structure is probably due to extremely cold conditions in 1996 impacting on a fish community exposed to historically high fishing rates. After 1999 the fish community variables such as biomass, abundance, mean weight, P/D ratio as well as community composition did not return to levels of the early 90s, although fishing pressure and climatic conditions returned to earlier levels. PMID:23658646

  6. Benchmark model to assess community structure in evolving networks.

    PubMed

    Granell, Clara; Darst, Richard K; Arenas, Alex; Fortunato, Santo; Gómez, Sergio

    2015-07-01

    Detecting the time evolution of the community structure of networks is crucial to identify major changes in the internal organization of many complex systems, which may undergo important endogenous or exogenous events. This analysis can be done in two ways: considering each snapshot as an independent community detection problem or taking into account the whole evolution of the network. In the first case, one can apply static methods on the temporal snapshots, which correspond to configurations of the system in short time windows, and match afterward the communities across layers. Alternatively, one can develop dedicated dynamic procedures so that multiple snapshots are simultaneously taken into account while detecting communities, which allows us to keep memory of the flow. To check how well a method of any kind could capture the evolution of communities, suitable benchmarks are needed. Here we propose a model for generating simple dynamic benchmark graphs, based on stochastic block models. In them, the time evolution consists of a periodic oscillation of the system's structure between configurations with built-in community structure. We also propose the extension of quality comparison indices to the dynamic scenario. PMID:26274223

  7. Gap formation following climatic events in spatially structured plant communities.

    PubMed

    Liao, Jinbao; De Boeck, Hans J; Li, Zhenqing; Nijs, Ivan

    2015-01-01

    Gaps play a crucial role in maintaining species diversity, yet how community structure and composition influence gap formation is still poorly understood. We apply a spatially structured community model to predict how species diversity and intraspecific aggregation shape gap patterns emerging after climatic events, based on species-specific mortality responses. In multispecies communities, average gap size and gap-size diversity increased rapidly with increasing mean mortality once a mortality threshold was exceeded, greatly promoting gap recolonization opportunity. This result was observed at all levels of species richness. Increasing interspecific difference likewise enhanced these metrics, which may promote not only diversity maintenance but also community invasibility, since more diverse niches for both local and exotic species are provided. The richness effects on gap size and gap-size diversity were positive, but only expressed when species were sufficiently different. Surprisingly, while intraspecific clumping strongly promoted gap-size diversity, it hardly influenced average gap size. Species evenness generally reduced gap metrics induced by climatic events, so the typical assumption of maximum evenness in many experiments and models may underestimate community diversity and invasibility. Overall, understanding the factors driving gap formation in spatially structured assemblages can help predict community secondary succession after climatic events. PMID:26114803

  8. Experimental sulfate amendment alters peatland bacterial community structure.

    PubMed

    Strickman, R J S; Fulthorpe, R R; Coleman Wasik, J K; Engstrom, D R; Mitchell, C P J

    2016-10-01

    As part of a long-term, peatland-scale sulfate addition experiment, the impact of varying sulfate deposition on bacterial community responses was assessed using 16S tag encoded pyrosequencing. In three separate areas of the peatland, sulfate manipulations included an eight year quadrupling of atmospheric sulfate deposition (experimental), a 3-year recovery to background deposition following 5years of elevated deposition (recovery), and a control area. Peat concentrations of methylmercury (MeHg), a bioaccumulative neurotoxin, were measured, the production of which is attributable to a growing list of microorganisms, including many sulfate-reducing Deltaproteobacteria. The total bacterial and Deltaproteobacterial community structures in the experimental treatment differed significantly from those in the control and recovery treatments that were either indistinguishable or very similar to one another. Notably, the relatively rapid return (within three years) of bacterial community structure in the recovery treatment to a state similar to the control, demonstrates significant resilience of the peatland bacterial community to changes in atmospheric sulfate deposition. Changes in MeHg accumulation between sulfate treatments correlated with changes in the Deltaproteobacterial community, suggesting that sulfate may affect MeHg production through changes in the community structure of this group. PMID:27267720

  9. Prokaryotic community structure and respiration during long-term incubations

    PubMed Central

    Baltar, Federico; Lindh, Markus V; Parparov, Arkadi; Berman, Tom; Pinhassi, Jarone

    2012-01-01

    Despite the importance of incubation assays for studies in microbial ecology that frequently require long confinement times, few reports are available in which changes in the assemblage structure of aquatic prokaryotes were monitored during long-term incubations. We measured rates of dissolved organic carbon degradation and microbial respiration by consumption of dissolved oxygen (DO) in four experiments with Lake Kinneret near-surface water and, concomitantly, we analyzed the variability in prokaryotic community structure during long-term dark bottle incubations. During the first 24 h, there were only minor changes in bacterial community composition. Thereafter there were marked changes in the prokaryotic community structure during the incubations. In contrast, oxygen consumption rates (a proxy for both respiration and dissolved organic carbon degradation rates) remained stable for up to 10–23 days. This study is one of the first to examine closely the phylo-genetic changes that occur in the microbial community of untreated freshwater during long-term (days) incubations in dark, sealed containers. Novel information on the diversity of the main bacterial phylotypes that may be involved in dissolved organic matter degradation in lake Kinneret is also provided. Our results suggest that, under certain ecological settings, constant community metabolic rates can be maintained as a result of shifts in community composition. PMID:22950026

  10. Benchmark model to assess community structure in evolving networks

    NASA Astrophysics Data System (ADS)

    Granell, Clara; Darst, Richard K.; Arenas, Alex; Fortunato, Santo; Gómez, Sergio

    2015-07-01

    Detecting the time evolution of the community structure of networks is crucial to identify major changes in the internal organization of many complex systems, which may undergo important endogenous or exogenous events. This analysis can be done in two ways: considering each snapshot as an independent community detection problem or taking into account the whole evolution of the network. In the first case, one can apply static methods on the temporal snapshots, which correspond to configurations of the system in short time windows, and match afterward the communities across layers. Alternatively, one can develop dedicated dynamic procedures so that multiple snapshots are simultaneously taken into account while detecting communities, which allows us to keep memory of the flow. To check how well a method of any kind could capture the evolution of communities, suitable benchmarks are needed. Here we propose a model for generating simple dynamic benchmark graphs, based on stochastic block models. In them, the time evolution consists of a periodic oscillation of the system's structure between configurations with built-in community structure. We also propose the extension of quality comparison indices to the dynamic scenario.

  11. Algal culture studies for CELSS

    NASA Technical Reports Server (NTRS)

    Radmer, R.; Behrens, P.; Arnett, K.; Gladue, R.; Cox, J.; Lieberman, D.

    1987-01-01

    Microalgae are well-suited as a component of a Closed Environmental Life Support System (CELSS), since they can couple the closely related functions of food production and atmospheric regeneration. The objective was to provide a basis for predicting the response of CELSS algal cultures, and thus the food supply and air regeneration system, to changes in the culture parameters. Scenedesmus growth was measured as a function of light intensity, and the spectral dependence of light absorption by the algae as well as algal respiration in the light were determined as a function of cell concentration. These results were used to test and confirm a mathematical model that describes the productivity of an algal culture in terms of the competing processes of photosynthesis and respiration. The relationship of algal productivity to cell concentration was determined at different carbon dioxide concentrations, temperatures, and light intensities. The maximum productivity achieved by an air-grown culture was found to be within 10% of the computed maximum productivity, indicating that CO2 was very efficiently removed from the gas stream by the algal culture. Measurements of biomass productivity as a function of cell concentration at different light intensities indicated that both the productivity and efficiency of light utilization were greater at higher light intensities.

  12. Biodiversity of zoobenthic hard-substrate sublittoral communities in the Eastern Mediterranean (North Aegean Sea)

    NASA Astrophysics Data System (ADS)

    Antoniadou, Chryssanthi; Chintiroglou, Chariton

    2005-03-01

    The spatial dispersion of zoobenthos from sublittoral hard substrate communities in the northern part of the Aegean Sea has been studied during summer 1997 and 1998. Material was collected by SCUBA diving, by totally scraping off five replicate quadrates (400 cm 2 each) at three depth levels (15, 30, 40 m) from six sites located in Chalkidiki peninsula, plus one in Kavala Gulf. The examination of the 19,343 living specimens collected revealed the presence of 314 species. Though the multivariate analyses showed high similarity between stations, the structure of this sciaphilic algal community seems to have an increased spatial heterogeneity. Four distinct facies were recorded in accordance with the occurrence of different algal forms, the degree of hard substrate inclination and the water clarity. A short review on the biodiversity of sublittoral communities in the Mediterranean revealed the affinity between the western and the eastern basin and also among the photophilic and the sciaphilic algal communities.

  13. An optical system for detecting and describing major algal blooms in coastal and oceanic waters around India

    NASA Astrophysics Data System (ADS)

    Gokul, Elamurugu Alias; Shanmugam, Palanisamy

    2016-06-01

    An optical system is developed with the aim to detect and monitor three major algal blooms (including harmful algal blooms "HABs") over ecologically relevant scales around India and to strengthen algal forecasting system. This system is designed to be capable of utilizing remote sensing, in situ, and radiative transfer techniques to provide species-specific data necessary for increasing capabilities of an algal forecasting system. With the ability to measure in-water optical properties by means of remote sensing and in situ observations, the optical system developed infers the desired phytoplankton signal from spectral distributions and utilize these data in a numerical classification technique to generate species-specific maps at given spatial and temporal scales. A simple radiative transfer model is adopted for this system to provide a means to optimally interpolate to regions with sparse in situ observation data and to provide a central component to generate in-water optical properties from remotely sensed data. For a given set of inherent optical properties along with surface and bottom boundary conditions, the optical system potentially provides researchers and managers coverage at different locations and depths for tracking algal blooms in the water column. Three major algal blooms focused here include Noctiluca scintillans/miliaris, Trichodesmium erythraeum, and Cochlodinium polykrikoides, which are recurring events in coastal and oceanic waters around India. Because satellite sensors provide a synoptic view of the ocean, both spatially and temporally, our initial efforts tested this optical system using several MODIS-Aqua images and ancillary data. Validation of the results with coincident in situ data obtained from either surface samples or depth samples demonstrated the robustness and potential utility of this approach, with an accuracy of 80-90% for delineating the presence of all three blooms in a heterogeneous phytoplankton community. Despite its

  14. Biological interactions and their role in community structure in the rocky intertidal of Helgoland (German Bight, North Sea)

    NASA Astrophysics Data System (ADS)

    Janke, Klaus

    1990-06-01

    Over 3 successive seasonal cycles (April 1986 to October 1988), field experiments were established within 3 intertidal levels in the sheltered rocky intertidal of Helgoland (North Sea, German Bight). Competitors for space ( Mytilus edulis, macroalgae), herbivores ( Littorina spp.) and predators ( Carcinus maenas) were either excluded from areas (0.25 m2) covered by undisturbed communities or enclosed at natural densities on areas that were cleared before of animals and plants. All the experimental fields (each 0.25 m2) were covered by cages with 4 mm gauze at the sides and a plexiglas top. The results of the experiments in the upper intertidal (occupied by Littorina spp. and Enteromorpha) showed that a natural density of herbivores could not prevent algal settlement and had only little influence on algal growth. Instead abiotic factors (storms, algae washed ashore) decreased the stock of the green algae. Experiments in the mid intertidal, dominated by Mytilus (50% cover), Fucus spp. (20%) and grazing L. littorea (100 ind. m-2) showed that community structure was directly changed both by grazing periwinkles and by competition for space between mussels and macroalgae. Whenever Littorina was excluded, the canopy of Fucus spp. increased continuously and reached total cover within two years. In addition to the increase of Fucus spp., the rock surface and the mussel shells were overgrown by Ulva pseudocurvata, which covered the experimental fields during parts of the summer in the absence of herbivores. As soon as perennial species (fucoids) covered most of the experimental areas, the seasonal growth of Ulva decreased drastically. Presence and growth of macroalgae were also controlled by serious competition for space with mussels. Established Mytilus prevented the growth of all perennial and ephemeral algae on the rocks. However, the shells of the mussels provided free space for a new settlement of Fucus and Ulva. In the lower intertidal (dominated by total algal cover

  15. Governance and Management Structures for Community Partnerships: Experiences from the Robert Wood Johnson Foundation's Community Partnerships for Older Adults Program

    ERIC Educational Resources Information Center

    Bolda, Elise J.; Saucier, Paul; Maddux, George L.; Wetle, Terrie; Lowe, Jane Isaacs

    2006-01-01

    Purpose: This article describes early efforts of four community partnerships in Boston, El Paso, Houston, and Milwaukee to address governance and management structures in ways that promote the sustainability of innovative community-based long-term care system improvements. The four communities are grantees of the Community Partnerships for Older…

  16. Assessment of ecological conditions and potential effects of water produced from coalbed natural gas development on biological communities in streams of the Powder River structural basin, Wyoming and Montana, 2005-08

    USGS Publications Warehouse

    Peterson, David A.; Clark, Melanie L.; Foster, Katharine; Wright, Peter R.; Boughton, Gregory K.

    2010-01-01

    Ongoing development of coalbed natural gas in the Powder River structural basin in Wyoming and Montana led to formation of an interagency task group to address concerns about the effects of the resulting production water on biological communities in streams of the area. The interagency task group developed a monitoring plan and conducted sampling of macroinvertebrate, algal, and fish communities at 47 sites during 2005-08 to document current ecological conditions and determine existing and potential effects of water produced from coalbed natural gas development on biological communities. Macroinvertebrate, algal, and fish community composition varied between drainage basins, among sites within drainage basins, and by year. Macroinvertebrate communities of the main-stem Tongue River were characterized by higher taxa richness and higher abundance of Ephemeroptera, for example, compared to macroinvertebrate communities in plains tributaries of the Tongue River and the main-stem Powder River. Fish communities of the Tongue River were characterized by higher taxa richness and abundance of introduced species compared to the Powder River where native species were dominant. Macroinvertebrate community metric values from sites in the middle reach of the main-stem Powder River, from below Willow Creek to below Crazy Woman Creek, differed from metric values in the upper and lower reaches of the Powder River. Metrics indicative of communitywide differences included measures of taxa richness, relative abundance, feeding mode, and tolerance. Some of the variation in the macroinvertebrate communities could be explained by variation in environmental variables, including physical (turbidity, embeddedness, bed substrate size, and streamflow) and chemical (alkalinity and specific conductance) variables. Of these environmental variables, alkalinity was the best indicator of coalbed natural gas development because of the sodiumbicarbonate signature of the production water. Algal

  17. The effects of climate variability on the structure of the phytoplankton community in Tumaco Bay, Colombia

    NASA Astrophysics Data System (ADS)

    Honkala, Ingrid Garcia-Hansen

    2009-12-01

    Canonical Correspondence Analysis (CCA). Strong gradients in temperature, salinity, nutrients and Secchi depth (water clarity) correlated predominantly with diatom and dinoflagellate community structure. Seasonal variability in the communities provided some important findings: (1) increased species richness and abundance of both groups were correlated with increased nutrients during the cold phase/RS; (2) diatom blooms occurred during the cold phase; (3) dinoflagellate blooms occurred at the beginning of the warm phase; (4) decreased species richness and abundance and lack of blooms characterized the DS; (5) abundances were higher nearshore than at the offshore part of the bay; and (6) chl a concentrations increased during the cold phase. The influence of ENSO in the communities also provided some important observations: (1) species richness and abundance of diatoms increased during La Nina; (2) species richness and abundance of dinoflagellates increased during El Nino when precipitation and nutrients were high; (3) harmful species and harmful algal blooms (HAB) increased during ENSO events; (4) communities recovered quickly after El Nino events; and (5) chl a concentrations decreased during El Nino and increased during Normal and La Nina conditions.

  18. Genetic and acute toxicological evaluation of an algal oil containing eicosapentaenoic acid (EPA) and palmitoleic acid.

    PubMed

    Collins, M L; Lynch, B; Barfield, W; Bull, A; Ryan, A S; Astwood, J D

    2014-10-01

    Algal strains of Nannochloropsis sp. were developed, optimized, cultivated and harvested to produce a unique composition of algal oil ethyl esters (Algal-EE) that are naturally high in eicosapentaenoic acid (EPA, 23-30%) and palmitoleic acid (20-25%), and contain no docosahexaenoic acid (DHA). Algal-EE was evaluated for mutagenic activity (Ames bacterial reverse mutation, in vitro mammalian chromosome aberration, in vivo micronucleus test) and for acute oral toxicity in Sprague-Dawley rats. In the acute toxicity study, rats received a single oral gavaged dose of Algal-EE (2000 mg/kg body weight). Clinical observations were made for 14 days before sacrifice on Day 15. Macroscopic evaluation involved the examination of all organs in the cranial, thoracic, and abdominal cavities. Algal-EE showed no evidence of mutagenicity, did not produce an increase in the frequency of structural chromosome aberrations, and did not cause an increase in the induction of micronucleated polychromatic erythrocytes. There were no macroscopic abnormalities. Algal-EE up to 2000 mg/kg body weight did not affect body weight, organ appearance or produce any toxic-related signs of morbidity. The acute median lethal dose (LD50) of Algal-EE was >2000 mg/kg body weight. Based on these assays, Algal-EE does not appear to have any genetic or acute oral toxicity. PMID:25057807

  19. Phylogenetic plant community structure along elevation is lineage specific

    PubMed Central

    Ndiribe, Charlotte; Pellissier, Loïc; Antonelli, Silvia; Dubuis, Anne; Pottier, Julien; Vittoz, Pascal; Guisan, Antoine; Salamin, Nicolas

    2013-01-01

    The trend of closely related taxa to retain similar environmental preferences mediated by inherited traits suggests that several patterns observed at the community scale originate from longer evolutionary processes. While the effects of phylogenetic relatedness have been previously studied within a single genus or family, lineage-specific effects on the ecological processes governing community assembly have rarely been studied for entire communities or flora. Here, we measured how community phylogenetic structure varies across a wide elevation gradient for plant lineages represented by 35 families, using a co-occurrence index and net relatedness index (NRI). We propose a framework that analyses each lineage separately and reveals the trend of ecological assembly at tree nodes. We found prevailing phylogenetic clustering for more ancient nodes and overdispersion in more recent tree nodes. Closely related species may thus rapidly evolve new environmental tolerances to radiate into distinct communities, while older lineages likely retain inherent environmental tolerances to occupy communities in similar environments, either through efficient dispersal mechanisms or the exclusion of older lineages with more divergent environmental tolerances. Our study illustrates the importance of disentangling the patterns of community assembly among lineages to better interpret the ecological role of traits. It also sheds light on studies reporting absence of phylogenetic signal, and opens new perspectives on the analysis of niche and trait conservatism across lineages. PMID:24455126

  20. Evidence of Community Structure in Biomedical Research Grant Collaborations

    PubMed Central

    Nagarajan, Radhakrishnan; Kalinka, Alex T; Hogan, William R

    2014-01-01

    Recent studies have clearly demonstrated a shift towards collaborative research and team science approaches across a spectrum of disciplines. Such collaborative efforts have also been acknowledged and nurtured by popular extramurally funded programs including the Clinical Translational Science Award (CTSA) conferred by the National Institutes of Health. Since its inception, the number of CTSA awardees has steadily increased to 60 institutes across 30 states. One of the objectives of CTSA is to accelerate translation of research from bench to bedside to community and train a new genre of researchers under the translational research umbrella. Feasibility of such a translation implicitly demands multi-disciplinary collaboration and mentoring. Networks have proven to be convenient abstractions for studying research collaborations. The present study is a part of the CTSA baseline study and investigates existence of possible community-structure in Biomedical Research Grant Collaboration (BRGC) networks across data sets retrieved from the internally developed grants management system, the Automated Research Information Administrator (ARIA) at the University of Arkansas for Medical Sciences (UAMS). Fastgreedy and link-community community-structure detection algorithms were used to investigate the presence of non-overlapping and overlapping community-structure and their variation across years 2006 and 2009. A surrogate testing approach in conjunction with appropriate discriminant statistics, namely: the Modularity Index and the Maximum Partition Density is proposed to investigate whether the community-structure of the BRGC networks were different from those generated by certain types of random graphs. Non-overlapping as well as overlapping community-structure detection algorithms indicated the presence of community-structure in the BRGC network. Subsequent, surrogate testing revealed that random graph models considered in the present study may not necessarily be appropriate

  1. Understanding and mitigating tsunami risk for coastal structures and communities

    NASA Astrophysics Data System (ADS)

    Park, Sangki

    Tsunamis have attracted the world's attention over the last decade due to their destructive power and the vast areas they can affect. The 2004 Indian Ocean Tsunami, killed more than 200,000 people, and the 2011 Great Tohoku Japan Earthquake and Tsunami, resulted in 15,000 deaths and an estimated US $300B in damage, are recent examples. An improved understanding of tsunamis and their interactive effects on the built environment will significantly reduce loss of life in tsunamis. In addition, it is important to consider both the effect of the earthquake ground motion and the tsunami it creates for certain coastal regions. A numerical model to predict structural behavior of buildings subjected to successive earthquakes and the tsunamis was developed. Collapse fragilities for structures were obtained by subjecting a structure to a suite of earthquake ground motions. After each motion the numerically damaged structural model was subjected to tsunami wave loading as defined by FEMA P646. This approach was then extended to the community level; a methodology to determine the probability of fatalities for a community as a function of the number of vertical evacuation shelters was computed. Such an approach also considered the location and number of vertical evacuation sites as an optimization problem. Both the single structure cases and the community analyses were presented in terms of fragilities as a function of the earthquake intensity level and evacuation time available. It is envisioned that the approach may be extended to any type of structure as they are typically modeled nonlinearly with strength and stiffness degradation. A logical fragility-based, or performance-based, procedure for vertical evacuation for coastal buildings and for whole communities was developed. A mechanism to obtain a reduction in the collapse risk of structure and more critically maximize the survival rate for a community was a major outcome of this dissertation. The proposed tsunami vertical

  2. Extinction order and altered community structure rapidly disrupt ecosystem functioning.

    PubMed

    Larsen, Trond H; Williams, Neal M; Kremen, Claire

    2005-05-01

    By causing extinctions and altering community structure, anthropogenic disturbances can disrupt processes that maintain ecosystem integrity. However, the relationship between community structure and ecosystem functioning in natural systems is poorly understood. Here we show that habitat loss appeared to disrupt ecosystem functioning by affecting extinction order, species richness and abundance. We studied pollination by bees in a mosaic of agricultural and natural habitats in California and dung burial by dung beetles on recently created islands in Venezuela. We found that large-bodied bee and beetle species tended to be both most extinction-prone and most functionally efficient, contributing to rapid functional loss. Simulations confirmed that extinction order led to greater disruption of function than predicted by random species loss. Total abundance declined with richness and also appeared to contribute to loss of function. We demonstrate conceptually and empirically how the non-random response of communities to disturbance can have unexpectedly large functional consequences. PMID:21352458

  3. Exponential random graph models for networks with community structure

    NASA Astrophysics Data System (ADS)

    Fronczak, Piotr; Fronczak, Agata; Bujok, Maksymilian

    2013-09-01

    Although the community structure organization is an important characteristic of real-world networks, most of the traditional network models fail to reproduce the feature. Therefore, the models are useless as benchmark graphs for testing community detection algorithms. They are also inadequate to predict various properties of real networks. With this paper we intend to fill the gap. We develop an exponential random graph approach to networks with community structure. To this end we mainly built upon the idea of blockmodels. We consider both the classical blockmodel and its degree-corrected counterpart and study many of their properties analytically. We show that in the degree-corrected blockmodel, node degrees display an interesting scaling property, which is reminiscent of what is observed in real-world fractal networks. A short description of Monte Carlo simulations of the models is also given in the hope of being useful to others working in the field.

  4. Family Structure, Community Context, and Adolescent Problem Behaviors

    ERIC Educational Resources Information Center

    Hoffman, John P.

    2006-01-01

    A number of models have been proposed to explain the relationship between family structure and adolescent problem behaviors, including several that consider parent-child relations, family income, stress, and residential mobility. However, studies have not explored whether the different types of communities within which families reside affect the…

  5. MICROBIAL COMMUNITY STRUCTURE AND ENZYME ACTIVITIES IN SEMIARID AGRICULTURAL SOILS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The effect of management on the microbial community structure and enzyme activities of three semiarid soils from Southern High Plains of Texas were investigated. The soils (sandy clay loam, fine sandy loam and loam) were under continuous cotton (Gossypium hirsutum L.) or in cotton -peanut (Arachis h...

  6. Changes in Soil Microbial Community Structure with Flooding

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Flooding disturbs both above- and below-ground ecosystem processes. Although often ignored, changes in below-ground environments are no less important than those that occur above-ground. Shifts in soil microbial community structure are expected when anaerobic conditions develop from flooding. The ...

  7. Changes in Age Structure and Rural Community Growth.

    ERIC Educational Resources Information Center

    McGranahan, David A.

    1985-01-01

    Whatever migration patterns evolve, changes in the age structure mean that rural communities in general can expect fairly stable elementary school population, reduced high school population, slower growth in new business and employment, and continued increase in the elderly population. (JHZ)

  8. The Community Context of Family Structure and Adolescent Drug Use.

    ERIC Educational Resources Information Center

    Hoffmann, John P.

    2002-01-01

    Investigates hypothesis used to explain the relationship between family structure and adolescent drug use, using data from the National Education Longitudinal Study (NELS). Reports that adolescents who resided in single-parent or stepparent families had heightened drug use. Higher adolescent drug use was found in communities with a large…

  9. Relating methanogen community structure and anaerobic digester function.

    PubMed

    Bocher, B T W; Cherukuri, K; Maki, J S; Johnson, M; Zitomer, D H

    2015-03-01

    Much remains unknown about the relationships between microbial community structure and anaerobic digester function. However, knowledge of links between community structure and function, such as specific methanogenic activity (SMA) and COD removal rate, are valuable to improve anaerobic bioprocesses. In this work, quantitative structure-activity relationships (QSARs) were developed using multiple linear regression (MLR) to predict SMA using methanogen community structure descriptors for 49 cultures. Community descriptors were DGGE demeaned standardized band intensities for amplicons of a methanogen functional gene (mcrA). First, predictive accuracy of MLR QSARs was assessed using cross validation with training (n = 30) and test sets (n = 19) for glucose and propionate SMA data. MLR equations correlating band intensities and SMA demonstrated good predictability for glucose (q(2) = 0.54) and propionate (q(2) = 0.53). Subsequently, data from all 49 cultures were used to develop QSARs to predict SMA values. Higher intensities of two bands were correlated with higher SMA values; high abundance of methanogens associated with these two bands should be encouraged to attain high SMA values. QSARs are helpful tools to identify key microorganisms or to study and improve many bioprocesses. Development of new, more robust QSARs is encouraged for anaerobic digestion or other bioprocesses, including nitrification, nitritation, denitrification, anaerobic ammonium oxidation, and enhanced biological phosphorus removal. PMID:25562581

  10. Diatom Derived Polyunsaturated Aldehydes Do Not Structure the Planktonic Microbial Community in a Mesocosm Study

    PubMed Central

    Paul, Carsten; Reunamo, Anna; Lindehoff, Elin; Bergkvist, Johanna; Mausz, Michaela A.; Larsson, Henrik; Richter, Hannes; Wängberg, Sten-Åke; Leskinen, Piia; Båmstedt, Ulf; Pohnert, Georg

    2012-01-01

    Several marine and freshwater diatoms produce polyunsaturated aldehydes (PUA) in wound-activated processes. These metabolites are also released by intact diatom cells during algal blooms. Due to their activity in laboratory experiments, PUA are considered as potential mediators of diatom-bacteria interactions. Here, we tested the hypothesis that PUA mediate such processes in a close-to-field mesocosm experiment. Natural plankton communities enriched with Skeletonema marinoi strains that differ in their PUA production, a plankton control, and a plankton control supplemented with PUA at natural and elevated concentrations were observed. We monitored bacterial and viral abundance as well as bacterial community composition and did not observe any influence of PUA on these parameters even at elevated concentrations. We rather detected an alternation of the bacterial diversity over time and differences between the two S. marinoi strains, indicating unique dynamic bacterial communities in these algal blooms. These results suggest that factors other than PUA are of significance for interactions between diatoms and bacteria. PMID:22690143

  11. Photoautotrophic symbiont and geography are major factors affecting highly structured and diverse bacterial communities in the lichen microbiome

    SciTech Connect

    Hodkinson, Brendan P; Gottel, Neil R; Schadt, Christopher Warren; Lutzoni, Francois

    2011-01-01

    Although common knowledge dictates that the lichen thallus is formed solely by a fungus (mycobiont) that develops a symbiotic relationship with an alga and/or cyanobacterium (photobiont), the non-photoautotrophic bacteria found in lichen microbiomes are increasingly regarded as integral components of lichen thalli. For this study, comparative analyses were conducted on lichen-associated bacterial communities to test for effects of photobiont-types (i.e. green algal vs. cyanobacterial), mycobiont-types and large-scale spatial distances (from tropical to arctic latitudes). Amplicons of the 16S (SSU) rRNA gene were examined using both Sanger sequencing of cloned fragments and barcoded pyrosequencing. Rhizobiales is typically the most abundant and taxonomically diverse order in lichen microbiomes; however, overall bacterial diversity in lichens is shown to be much higher than previously reported. Members of Acidobacteriaceae, Acetobacteraceae, Brucellaceae and sequence group LAR1 are the most commonly found groups across the phylogenetically and geographically broad array of lichens examined here. Major bacterial community trends are significantly correlated with differences in large-scale geography, photobiont-type and mycobiont-type. The lichen as a microcosm represents a structured, unique microbial habitat with greater ecological complexity and bacterial diversity than previously appreciated and can serve as a model system for studying larger ecological and evolutionary principles.

  12. Community structure influences species' abundance along environmental gradients.

    PubMed

    Eloranta, Antti P; Helland, Ingeborg P; Sandlund, Odd T; Hesthagen, Trygve; Ugedal, Ola; Finstad, Anders G

    2016-01-01

    Species' response to abiotic environmental variation can be influenced by local community structure and interspecific interactions, particularly in restricted habitats such as islands and lakes. In temperate lakes, future increase in water temperature and run-off of terrestrial (allochthonous) dissolved organic carbon (DOC) are predicted to alter community composition and the overall ecosystem productivity. However, little is known about how the present community structure and abiotic environmental variation interact to affect the abundance of native fish populations. We used a space-for-time approach to study how local community structure interact with lake morphometric and climatic characteristics (i.e. temperature and catchment productivity) to affect brown trout (Salmo trutta L.) yield in 283 Norwegian lakes located in different biogeographical regions. Brown trout yield (based on data from standardized survey gill net fishing; g 100 m(-2) gill net night(-1)) was generally lower in lakes where other fish species were present than in lakes with brown trout only. The yield showed an overall negative relationship with increasing temperature and a positive relationship with lake shoreline complexity. Brown trout yield was also negatively correlated with DOC load (measured using Normalized Difference Vegetation Index as a proxy) and lake size and depth (measured using terrain slope as a proxy), but only in lakes where other fish species were present. The observed negative response of brown trout yield to increasing DOC load and proportion of the pelagic open-water area is likely due to restricted (littoral) niche availability and competitive dominance of more pelagic fishes such as Arctic charr (Salvelinus alpinus (L.)). Our study highlights that, through competitive interactions, the local community structure can influence the response of a species' abundance to variation in abiotic conditions. Changes in biomass and niche use of top predators (such as the brown

  13. Structure of Benthic Communities along the Taiwan Latitudinal Gradient

    PubMed Central

    De Palmas, Stéphane; Kuo, Chao-Yang; Hsieh, Hernyi Justin; Chen, Chaolun Allen

    2016-01-01

    The distribution and the structure of benthic assemblages vary with latitude. However, few studies have described benthic communities along large latitudinal gradients, and patterns of variation are not fully understood. Taiwan, lying between 21.90°N and 25.30°N, is located at the center of the Philippine-Japan arc and lies at the northern margin of coral reef development. A wide range of habitats is distributed along this latitudinal gradient, from extensive fringing coral reefs at the southern coast to non-reefal communities at the north. In this study, we examined the structure of benthic communities around Taiwan, by comparing its assemblages in four regions, analyzing the effects of the latitudinal gradient, and highlighting regional characteristics. A total of 25 sites, 125 transects, and 2,625 photographs were used to analyze the benthic communities. Scleractinian corals present an obvious gradient of increasing diversity from north to south, whereas macro-algae diversity is higher on the north-eastern coast. At the country scale, Taiwanese coral communities were dominated by turf algae (49%). At the regional scale, we observed an important heterogeneity that may be caused by local disturbances and habitat degradation that smooths out regional differences. In this context, our observations highlight the importance of managing local stressors responsible for reef degradation. Overall, this study provides an important baseline upon which future changes in benthic assemblages around Taiwan can be assessed. PMID:27513665

  14. Mutualistic Interactions and Community Structure in Biological Metacommunities

    NASA Astrophysics Data System (ADS)

    Rikvold, Per Arne; Filotas, Elise; Grant, Martin; Parrott, Lael

    2011-03-01

    The role of space in determining species coexistence and community structure is well established. However, previous studies mainly focus on simple competition and predation systems, and the role of mutualistic interspecies interactions is not well understood. Here we use a spatially explicit metacommunity model, in which new species enter by a mutation process, to study the effect of fitness-dependent dispersal on the structure of communities with interactions comprising mutualism, competition, and exploitation. We find that the diversity and interaction network undergo a nonequilibrium phase transition with increasing dispersal rate. Low dispersion rate favors spontaneous emergence of many dissimilar, strongly mutualistic and species-poor local communities. Due to the local dissimilarities, the global diversity is high. High dispersion rate promotes local biodiversity and supports similar, species-rich local communities with a wide range of interactions. The strong similarity between neighboring local communities leads to reduced global diversity. Supported by NSERC (Canada), FQRNT (Québec), NSF (U.S.A.)

  15. The microbial community structure of the cotton rat nose.

    PubMed

    Chaves-Moreno, Diego; Plumeier, Iris; Kahl, Silke; Krismer, Bernhard; Peschel, Andreas; Oxley, Andrew P A; Jauregui, Ruy; Pieper, Dietmar H

    2015-12-01

    The cotton rat nose is commonly used as a model for Staphylococcus aureus colonization, as it is both physiologically and anatomically comparable to the human nares and can be easily colonized by this organism. However, while the colonization of the human anterior nares has been extensively studied, the microbial community structure of cotton rat noses has not been reported so far. We describe here the microbial community structure of the cotton rat (Sigmodon hispidus) nose through next-generation sequencing of 16S rRNA gene amplicons covering the V1-V2 region and the analysis of nearly full length 16S rRNA genes of the major phylotypes. Roughly half of the microbial community was composed of two undescribed species of the genus Campylobacter, with phylotypes belonging to the genera Catonella, Acholeplasma, Streptobacillus and Capnocytophaga constituting the predominant community members. Thus, the nasal community of the cotton rat is uniquely composed of several novel bacterial species and may not reflect the complex interactions that occur in human anterior nares. Mammalian airway microbiota may, however, be a rich source of hitherto unknown microbes. PMID:26306992

  16. Structure of Benthic Communities along the Taiwan Latitudinal Gradient.

    PubMed

    Ribas-Deulofeu, Lauriane; Denis, Vianney; De Palmas, Stéphane; Kuo, Chao-Yang; Hsieh, Hernyi Justin; Chen, Chaolun Allen

    2016-01-01

    The distribution and the structure of benthic assemblages vary with latitude. However, few studies have described benthic communities along large latitudinal gradients, and patterns of variation are not fully understood. Taiwan, lying between 21.90°N and 25.30°N, is located at the center of the Philippine-Japan arc and lies at the northern margin of coral reef development. A wide range of habitats is distributed along this latitudinal gradient, from extensive fringing coral reefs at the southern coast to non-reefal communities at the north. In this study, we examined the structure of benthic communities around Taiwan, by comparing its assemblages in four regions, analyzing the effects of the latitudinal gradient, and highlighting regional characteristics. A total of 25 sites, 125 transects, and 2,625 photographs were used to analyze the benthic communities. Scleractinian corals present an obvious gradient of increasing diversity from north to south, whereas macro-algae diversity is higher on the north-eastern coast. At the country scale, Taiwanese coral communities were dominated by turf algae (49%). At the regional scale, we observed an important heterogeneity that may be caused by local disturbances and habitat degradation that smooths out regional differences. In this context, our observations highlight the importance of managing local stressors responsible for reef degradation. Overall, this study provides an important baseline upon which future changes in benthic assemblages around Taiwan can be assessed. PMID:27513665

  17. A framework for solving ill-structured community problems

    NASA Astrophysics Data System (ADS)

    Keller, William Cotesworth

    A multifaceted protocol for solving ill-structured community problems has been developed. It embodies the lessons learned from the past by refining and extending features of previous models from the systems thinkers, and the fields of behavioral decision making and creative problem solving. The protocol also embraces additional features needed to address the unique aspects of community decision situations. The essential elements of the protocol are participants from the community, a problem-solving process, a systems picture, a facilitator, a modified Delphi method of communications, and technical expertise. This interdisciplinary framework has been tested by a quasi experiment with a real world community problem (the high cost of electrical power on Long Island, NY). Results indicate the protocol can enable members of the community to understand a complicated, ill-structured problem and guide them to action to solve the issue. However, the framework takes time (over one year in the test case) and will be inappropriate for crises where quick action is needed.

  18. Quantifying the response of structural complexity and community composition to environmental change in marine communities.

    PubMed

    Ferrari, Renata; Bryson, Mitch; Bridge, Tom; Hustache, Julie; Williams, Stefan B; Byrne, Maria; Figueira, Will

    2016-05-01

    Habitat structural complexity is a key factor shaping marine communities. However, accurate methods for quantifying structural complexity underwater are currently lacking. Loss of structural complexity is linked to ecosystem declines in biodiversity and resilience. We developed new methods using underwater stereo-imagery spanning 4 years (2010-2013) to reconstruct 3D models of coral reef areas and quantified both structural complexity at two spatial resolutions (2.5 and 25 cm) and benthic community composition to characterize changes after an unprecedented thermal anomaly on the west coast of Australia in 2011. Structural complexity increased at both resolutions in quadrats (4 m(2)) that bleached, but not those that did not bleach. Changes in complexity were driven by species-specific responses to warming, highlighting the importance of identifying small-scale dynamics to disentangle ecological responses to disturbance. We demonstrate an effective, repeatable method for quantifying the relationship among community composition, structural complexity and ocean warming, improving predictions of the response of marine ecosystems to environmental change. PMID:26679689

  19. Correlations between Community Structure and Link Formation in Complex Networks

    PubMed Central

    Liu, Zhen; He, Jia-Lin; Kapoor, Komal; Srivastava, Jaideep

    2013-01-01

    Background Links in complex networks commonly represent specific ties between pairs of nodes, such as protein-protein interactions in biological networks or friendships in social networks. However, understanding the mechanism of link formation in complex networks is a long standing challenge for network analysis and data mining. Methodology/Principal Findings Links in complex networks have a tendency to cluster locally and form so-called communities. This widely existed phenomenon reflects some underlying mechanism of link formation. To study the correlations between community structure and link formation, we present a general computational framework including a theory for network partitioning and link probability estimation. Our approach enables us to accurately identify missing links in partially observed networks in an efficient way. The links having high connection likelihoods in the communities reveal that links are formed preferentially to create cliques and accordingly promote the clustering level of the communities. The experimental results verify that such a mechanism can be well captured by our approach. Conclusions/Significance Our findings provide a new insight into understanding how links are created in the communities. The computational framework opens a wide range of possibilities to develop new approaches and applications, such as community detection and missing link prediction. PMID:24039818

  20. Structure of phytoplankton communities in the Yenisei estuary and over the adjacent Kara Sea shelf

    NASA Astrophysics Data System (ADS)

    Sukhanova, I. N.; Flint, M. V.; Sergeeva, V. M.; Druzhkova, E. I.; Nedospasov, A. A.

    2015-11-01

    Material was collected in the Yenisei estuary and over the adjacent Kara Sea shelf at a quasimeridional transect from 71°49'70″ to 75°59'93″ N in September 2011. The structural characteristics of the phytoplankton community were determined by latitudinal zonality of environmental conditions. Two well-distinguished phytocenoses—freshwater and marine—were found in this region. Phytoplankton in the freshwater part of the estuary was composed solely of the freshwater algae species and was distinguished by the highest numbers (up to 2 × 106 cell/L) and biomass (up to 1.4 mg/L). The marine phytocenoses over the Yenisei shoal was composed of marine neritic species; the abundance and biomass of phytoplankton in this area were significantly lower (0.2 × 106 cell/L and 0.4 mg/L, respectively). The area of intensive interaction of riverine and marine waters—the estuarine frontal zone, with ~130 km latitudinal extension (from 72° to 74° N)—was characterized by a sharp halocline, which separated the desalinated upper layer from the underlying marine water. Freshwater algal species predominated above the halocline, whereas marine species predominated below. The lower border of the euphotic layer was located 8 to 15 m below the halocline. The niche between the halocline and the lower border of the euphotic layer was characterized by high nutrient concentrations, which together with sufficient illumination determined the intensive development of phytoplankton and high values of primary production.

  1. Climate and Species Richness Predict the Phylogenetic Structure of African Mammal Communities

    PubMed Central

    Kamilar, Jason M.; Beaudrot, Lydia; Reed, Kaye E.

    2015-01-01

    We have little knowledge of how climatic variation (and by proxy, habitat variation) influences the phylogenetic structure of tropical communities. Here, we quantified the phylogenetic structure of mammal communities in Africa to investigate how community structure varies with respect to climate and species richness variation across the continent. In addition, we investigated how phylogenetic patterns vary across carnivores, primates, and ungulates. We predicted that climate would differentially affect the structure of communities from different clades due to between-clade biological variation. We examined 203 communities using two metrics, the net relatedness (NRI) and nearest taxon (NTI) indices. We used simultaneous autoregressive models to predict community phylogenetic structure from climate variables and species richness. We found that most individual communities exhibited a phylogenetic structure consistent with a null model, but both climate and species richness significantly predicted variation in community phylogenetic metrics. Using NTI, species rich communities were composed of more distantly related taxa for all mammal communities, as well as for communities of carnivorans or ungulates. Temperature seasonality predicted the phylogenetic structure of mammal, carnivoran, and ungulate communities, and annual rainfall predicted primate community structure. Additional climate variables related to temperature and rainfall also predicted the phylogenetic structure of ungulate communities. We suggest that both past interspecific competition and habitat filtering have shaped variation in tropical mammal communities. The significant effect of climatic factors on community structure has important implications for the diversity of mammal communities given current models of future climate change. PMID:25875361

  2. Drivers of macroinvertebrate community structure in unmodified streams

    PubMed Central

    2014-01-01

    Often simple metrics are used to summarise complex patterns in stream benthic ecology, thus it is important to understand how well these metrics can explain the finer-scale underlying environmental variation often hidden by coarser-scale influences. I sampled 47 relatively pristine streams in the central North Island of New Zealand in 2007 and (1) evaluated the local-scale drivers of macroinvertebrate community structure as well as both diversity and biomonitoring metrics in this unmodified landscape, and (2) assessed whether these drivers were similar for commonly used univariate metrics and multivariate structure. The drivers of community metrics and multivariate structure were largely similar, with % canopy cover and resource supply metrics the most commonly identified environmental drivers in these pristine streams. For an area with little to no anthropogenic influence, substantial variation was explained in the macroinvertebrate community (up to 70% on the first two components of a partial least squares regression), with both uni- and multivariate approaches. This research highlights two important points: (1) the importance of considering natural underlying environmental variation when assessing the response to coarse environmental gradients, and (2) the importance of considering canopy cover presence when assessing the impact of stressors on stream macroinvertebrate communities. PMID:25024926

  3. THE STRUCTURE AND PROCESS OF SCHOOL-COMMUNITY RELATIONS. VOLUME III, THE STRUCTURE OF SCHOOL-COMMUNITY RELATIONS.

    ERIC Educational Resources Information Center

    CARTER, RICHARD F.; AND OTHERS

    TO EVALUATE STRUCTURAL COMPONENTS OF SCHOOL-COMMUNITY RELATIONS, 860 VARIABLES WERE DEFINED FROM THE LITERATURE AND GROUPED INTO 26 DIVISIONS FOR ASSESSMENT AGAINST FOUR SUMMARY CRITERION VARIABLES--(1) ACQUIESCENCE, THE DEGREE TO WHICH VOTERS IN A SCHOOL DISTRICT VIEW FINANCIAL ISSUES FAVORABLY, (2) PARTICIPATION, THE DEGREE TO WHICH VOTERS…

  4. Harmful Algal Blooms and Public Health

    PubMed Central

    Grattan, Lynn M.; Holobaugh, Sailor; Morris, J. Glenn

    2015-01-01

    The five most commonly recognized Harmful Algal Bloom related illnesses include Ciguatera poisoning, Paralytic Shellfish poisoning, Neurotoxin Shellfish poisoning, Diarrheic Shellfish Poisoning and Amnesic Shellfish poisoning. Although they are each the product of different toxins, toxin assemblages or HAB precursors these clinical syndromes have much in common. Exposure occurs through the consumption of fish or shellfish; routine clinical tests are not available for diagnosis; there is no known antidote for exposure; and the risk of these illnesses can negatively impact local fishing and tourism industries. Thus, illness prevention is of paramount importance to minimize human and public health risks. To accomplish this, close communication and collaboration is needed among HAB scientists, public health researchers and local, state and tribal health departments at academic, community outreach, and policy levels. PMID:27616971

  5. Carbon Accumulation and Microbial Community Structure in Reclaimed Mine Soils

    NASA Astrophysics Data System (ADS)

    Pfiffner, S. M.; Palumbo, A. V.; Tarver, J. D.; Fisher, S.; Cantu, J.; Brandt, C. C.

    2002-12-01

    The objective of this study was to investigate the potential for soil amendments to increase accumulation of carbon in reclaimed soils and the relationship between carbon and microbial community structure. Changes in community structure were determined by signature lipid biomarkers (SLBs) or phospholipid fatty acid methyl esters. PLFA provide estimates of the viable biomass, diversity of prokaryotic and eukaryotic diversity, and indications of physiological stress to the microbial community. Artificial neural network (ANN) analysis has been used to examine the relationship between microbial community structure and soil geochemistry. It was hypothesized that (1) soil amendments would cause changes in the structure of the microbial community and carbon content (2) changes in the structure of the microbial community would be vary between the types of amendments, and (3) analysis of the SLB with an artificial neural network (ANN) would distinguish treatment and provide a insight in to the relationship between changes in soil geochemistry and microbial community. Twenty soils samples from different field plots and at different soil horizon depths were analyzed. Biomass as estimated by PLFA analysis, ranged from 1.9 to 265 nmol/g, which corresponded to cell densities of 4.8 x107 to 6.6 x109 cells/g. In the Wall's Farm and Jenkin's Farm samples the microbial biomass decreased with depth. A horizon soils had biomass values of greater or equal to 120 nmol/g, followed by the A2 horizon,(70 to 100 nmol/g) and the weak B horizon at and (40 to 80 nmo/g). The A2 and B horizon samples showed higher relative abundance of mid-chain branched saturates that are indicative of gram positive prokaryotes and actinomycetes. At Well's Farm, the polyunsaturates indicative of eukaryotes were observed at higher abundances. These changes were related to both the prokaryotic and eukaryotic influences in the microbial community in response to the soil amendments. The correlation between

  6. ALGAL RESPONSE TO NUTRIENT ENRICHMENT IN FORESTED OLIGOTROPHIC STREAM(1).

    PubMed

    Veraart, Annelies J; Romaní, Anna M; Tornés, Elisabet; Sabater, Sergi

    2008-06-01

    Nutrient input in streams alters the density and species composition of attached algal communities in open systems. However, in forested streams, the light reaching the streambed (rather than the local nutrient levels) may limit the growth of these communities. A nutrient-enrichment experiment in a forested oligotrophic stream was performed to test the hypothesis that nutrient addition has only minor effects on the community composition of attached algae and cyanobacteria under light limitation. Moderate nutrient addition consisted of increasing basal phosphorus (P) concentrations 3-fold and basal nitrogen (N) concentrations 2-fold. Two upstream control reaches were compared to a downstream reach before and after nutrient addition. Nutrients were added continuously to the downstream reach for 1 year. Algal biofilms growing on ceramic tiles were sampled and identified for more than a year before nutrient addition to 12 months after. Diatoms were the most abundant taxonomic group in the three stream reaches. Nutrient enrichment caused significant variations in the composition of the diatom community. While some taxa showed significant decreases (e.g., Achnanthes minutissima, Gomphonema angustum), increases for other taxa (such as Rhoicosphenia abbreviata and Amphora ovalis) were detected in the enriched reach (for taxonomic authors, see Table 2). Epiphytic and adnate taxa of large size were enhanced, particularly during periods of favorable growth conditions (spring). Nutrients also caused a change in the algal chl a, which increased from 0.5-5.8 to 2.1-10.7 μg chl · cm(-2) . Our results indicate that in oligotrophic forested streams, long-term nutrient addition has significant effects on the algal biomass and community composition, which are detectable despite the low light availability caused by the tree canopy. Low light availability moderates but does not detain the long-term tendency toward a nutrient-tolerant community. Furthermore, the effects

  7. Impacts of Size Structure on Intraguild Predation in Pond Communities

    NASA Astrophysics Data System (ADS)

    Crumrine, P. W.

    2005-05-01

    Size structure, the degree to which individuals in a population vary in size, can greatly influence the dynamics of intraguild predation (IGP) within ecological communities. I manipulated the degree of size structure within assemblages of IG predators and IG prey to examine impacts on the direction and intensity of IGP in communities of larval dragonflies and larval water beetles. In pond enclosure studies, Pachydiplax longipennis (IG prey) mortality was lower when exposed to size structured assemblages of Anax junius (IG predator) than when exposed to only large A. junius at the same density. Effects of size-structured assemblages of A. junius on shared prey, Ischnura verticalis, were similar to the effects each size class alone at the same density. Separate experiments with Dytiscid water beetle larvae as IG predators and size-structured assemblages of A. junius as IG prey suggest that IG prey size structure plays only a limited role in mediating shared prey survival. These experiments highlight the importance of size structure as a characteristic that may promote the coexistence of predators in IGP systems.

  8. Protozoan community structure in a fractal soil environment.

    PubMed

    Finlay, B J; Fenchel, T

    2001-09-01

    Protozoan abundance was quantified, and 365 protozoan species were recorded, in 150 soil samples from an upland grassland in Scotland. Across the entire size range (2-200 pm) protozoan species richness varied by a factor of two, whereas abundance increased by a factor of 20 with decreasing body size. As the soil had fractal structure, the relatively flat species curve can be explained if spatial heterogeneity determines species number--for in a fractal environment, heterogeneity will be the same at all spatial scales. Community structure appeared to approach a temporary steady-state about six days after re-hydration of dried soil. A simple model based on combining the fractal character of increasing habitat area at smaller spatial scales, with the weight-specific energy requirements of protozoa, provided theoretical curves of abundance and biovolume on body size which provide a reasonable fit to real data. We suggest two possibilities--that the apparent competence of the theoretical model is fortuitous and the product of poorly understood dynamic elements of the trophic structure in the community; or that key elements of protozoan community structure in a fractal soil environment may be largely explained in terms of habitat space and energy requirements. PMID:11693659

  9. Redox Fluctuation Structures Microbial Communities in a Wet Tropical Soil

    PubMed Central

    Pett-Ridge, J.; Firestone, M. K.

    2005-01-01

    Frequent high-amplitude redox fluctuation may be a strong selective force on the phylogenetic and physiological composition of soil bacterial communities and may promote metabolic plasticity or redox tolerance mechanisms. To determine effects of fluctuating oxygen regimens, we incubated tropical soils under four treatments: aerobic, anaerobic, 12-h oxic/anoxic fluctuation, and 4-day oxic/anoxic fluctuation. Changes in soil bacterial community structure and diversity were monitored with terminal restriction fragment length polymorphism (T-RFLP) fingerprints. These profiles were correlated with gross N cycling rates, and a Web-based phylogenetic assignment tool was used to infer putative community composition from multiple fragment patterns. T-RFLP ordinations indicated that bacterial communities from 4-day oxic/anoxic incubations were most similar to field communities, whereas those incubated under consistently aerobic or anaerobic regimens developed distinctly different molecular profiles. Terminal fragments found in field soils persisted either in 4-day fluctuation/aerobic conditions or in anaerobic/12-h treatments but rarely in both. Only 3 of 179 total fragments were ubiquitous in all soils. Soil bacterial communities inferred from in silico phylogenetic assignment appeared to be dominated by Actinobacteria (especially Micrococcus and Streptomycetes), “Bacilli,” “Clostridia,” and Burkholderia and lost significant diversity under consistently or frequently anoxic incubations. Community patterns correlated well with redox-sensitive processes such as nitrification, dissimilatory nitrate reduction to ammonium (DNRA), and denitrification but did not predict patterns of more general functions such as N mineralization and consumption. The results suggest that this soil's indigenous bacteria are highly adapted to fluctuating redox regimens and generally possess physiological tolerance mechanisms which allow them to withstand unfavorable redox periods. PMID

  10. Relationships between fish, sea urchins and macroalgae: The structure of shallow rocky sublittoral communities in the Cyclades, Eastern Mediterranean

    NASA Astrophysics Data System (ADS)

    Giakoumi, Sylvaine; Cebrian, Emma; Kokkoris, Giorgos D.; Ballesteros, Enric; Sala, Enric

    2012-08-01

    Historical overfishing is the most likely explanation for the depletion of the shallow sublittoral communities in many areas not least in the Cyclades Archipelago, Greece. The present study is the first quantitative study of the shallow rocky sublittoral of the Cyclades based on in situ underwater surveys of algal cover, and fish and sea urchin abundance at 181 sampling sites in 25 islands to provide a baseline and investigate the relationship between these communities. Algal turf was the most abundant algal functional group, and canopy algae of the genus Cystoseira were more abundant at the northern islands. A range in fish biomass of almost two orders of magnitude was found across islands, but overall the Cyclades displayed much lower values than fished areas of the Western Mediterranean. We observed apex predators only in 25% of our sampling sites, and their biomass was uncorrelated to total fish biomass, indicating a depleted ecosystem. Sea urchin biomass was also low but similar to values found in other Mediterranean islands and was positively correlated with barrens. We observed a gradient of benthic community complexity from sea urchin barrens to communities dominated by Cystoseira spp. There was no correlation between sea urchins and their predators Diplodus spp., which presented extremely low densities.

  11. Algal taxonomy forum: Algal Taxonomist, Let Serendipity Reign!

    PubMed

    Druehl, Louis

    2013-04-01

    The publication of a mini-review by Olivier De Clerck et al. in this issue of the Journal of Phycology presented an opportunity to open a dialogue on challenges faced by contemporary algal taxonomists. The Editorial Office solicited the following two additional contributions in response to De Clerck et al.'s paper; the responses were edited solely for clarity, space and format. PMID:27008510

  12. Phylogenetic structure and host abundance drive disease pressure in communities.

    PubMed

    Parker, Ingrid M; Saunders, Megan; Bontrager, Megan; Weitz, Andrew P; Hendricks, Rebecca; Magarey, Roger; Suiter, Karl; Gilbert, Gregory S

    2015-04-23

    Pathogens play an important part in shaping the structure and dynamics of natural communities, because species are not affected by them equally. A shared goal of ecology and epidemiology is to predict when a species is most vulnerable to disease. A leading hypothesis asserts that the impact of disease should increase with host abundance, producing a 'rare-species advantage'. However, the impact of a pathogen may be decoupled from host abundance, because most pathogens infect more than one species, leading to pathogen spillover onto closely related species. Here we show that the phylogenetic and ecological structure of the surrounding community can be important predictors of disease pressure. We found that the amount of tissue lost to disease increased with the relative abundance of a species across a grassland plant community, and that this rare-species advantage had an additional phylogenetic component: disease pressure was stronger on species with many close relatives. We used a global model of pathogen sharing as a function of relatedness between hosts, which provided a robust predictor of relative disease pressure at the local scale. In our grassland, the total amount of disease was most accurately explained not by the abundance of the focal host alone, but by the abundance of all species in the community weighted by their phylogenetic distance to the host. Furthermore, the model strongly predicted observed disease pressure for 44 novel host species we introduced experimentally to our study site, providing evidence for a mechanism to explain why phylogenetically rare species are more likely to become invasive when introduced. Our results demonstrate how the phylogenetic and ecological structure of communities can have a key role in disease dynamics, with implications for the maintenance of biodiversity, biotic resistance against introduced weeds, and the success of managed plants in agriculture and forestry. PMID:25903634

  13. Diversity and dynamics of algal Megaviridae members during a harmful brown tide caused by the pelagophyte, Aureococcus anophagefferens.

    PubMed

    Moniruzzaman, Mohammad; Gann, Eric R; LeCleir, Gary R; Kang, Yoonja; Gobler, Christopher J; Wilhelm, Steven W

    2016-05-01

    Many giant dsDNA algal viruses share a common ancestor with Mimivirus--one of the largest viruses, in terms of genetic content. Together, these viruses form the proposed 'Megaviridae' clade of nucleocytoplasmic large DNA viruses. To gauge Megaviridae diversity, we designed degenerate primers targeting the major capsid protein genes of algae-infecting viruses within this group and probed the clade's diversity during the course of a brown tide bloom caused by the harmful pelagophyte,Aureococcus anophagefferens We amplified target sequences in water samples from two distinct locations (Weesuck Creek and Quantuck Bay, NY) covering 12 weeks concurrent with the proliferation and demise of a bloom. In total, 475 amplicons clustered into 145 operational taxonomic units (OTUs) at 97% identity. One OTU contained 19 sequences with ≥97% identity to AaV, a member of the Megaviridae clade that infects A. anophagefferens, suggesting AaV was present during the bloom. Unifrac analysis showed clear temporal patterns in algal Megaviridae dynamics, with a shift in the virus community structure that corresponded to the Aureococcus bloom decline in both locations. Our data provide insights regarding the environmental relevance of algal Megaviridae members and raise important questions regarding their phylodynamics across different environmental gradients. PMID:26985013

  14. Community structure of non-coding RNA interaction network.

    PubMed

    Nacher, Jose C

    2013-01-01

    Rapid technological advances have shown that the ratio of non-protein coding genes rises to 98.5% in humans, suggesting that current knowledge on genetic information processing might be largely incomplete. It implies that protein-coding sequences only represent a small fraction of cellular transcriptional information. Here, we examine the community structure of the network defined by functional interactions between non-coding RNAs (ncRNAs) and proteins related bio-macromolecules (PRMs) using a two-fold approach: modularity in bipartite network and k-clique community detection. First, the high modularity scores as well as the distribution of community sizes showing a scaling-law revealed manifestly non-random features. Second, the k-clique sub-graphs and overlaps show that the identified communities of the ncRNA molecules of H. sapiens can potentially be associated with certain functions. These findings highlight the complex modular structure of ncRNA interactions and its possible regulatory roles in the cell. PMID:23545211

  15. Systems modeling approaches for microbial community studies: from metagenomics to inference of the community structure.

    PubMed

    Hanemaaijer, Mark; Röling, Wilfred F M; Olivier, Brett G; Khandelwal, Ruchir A; Teusink, Bas; Bruggeman, Frank J

    2015-01-01

    Microbial communities play important roles in health, industrial applications and earth's ecosystems. With current molecular techniques we can characterize these systems in unprecedented detail. However, such methods provide little mechanistic insight into how the genetic properties and the dynamic couplings between individual microorganisms give rise to their dynamic activities. Neither do they give insight into what we call "the community state", that is the fluxes and concentrations of nutrients within the community. This knowledge is a prerequisite for rational control and intervention in microbial communities. Therefore, the inference of the community structure from experimental data is a major current challenge. We will argue that this inference problem requires mathematical models that can integrate heterogeneous experimental data with existing knowledge. We propose that two types of models are needed. Firstly, mathematical models that integrate existing genomic, physiological, and physicochemical information with metagenomics data so as to maximize information content and predictive power. This can be achieved with the use of constraint-based genome-scale stoichiometric modeling of community metabolism which is ideally suited for this purpose. Next, we propose a simpler coarse-grained model, which is tailored to solve the inference problem from the experimental data. This model unambiguously relate to the more detailed genome-scale stoichiometric models which act as heterogeneous data integrators. The simpler inference models are, in our opinion, key to understanding microbial ecosystems, yet until now, have received remarkably little attention. This has led to the situation where the modeling of microbial communities, using only genome-scale models is currently more a computational, theoretical exercise than a method useful to the experimentalist. PMID:25852671

  16. Analysis of the community structure of abyssal kinetoplastids revealed similar communities at larger spatial scales

    PubMed Central

    Salani, Faezeh Shah; Arndt, Hartmut; Hausmann, Klaus; Nitsche, Frank; Scheckenbach, Frank

    2012-01-01

    Knowledge of the spatial scales of diversity is necessary to evaluate the mechanisms driving biodiversity and biogeography in the vast but poorly understood deep sea. The community structure of kinetoplastids, an important group of microbial eukaryotes belonging to the Euglenozoa, from all abyssal plains of the South Atlantic and two areas of the eastern Mediterranean was studied using partial small subunit ribosomal DNA gene clone libraries. A total of 1364 clones from 10 different regions were retrieved. The analysis revealed statistically not distinguishable communities from both the South-East Atlantic (Angola and Guinea Basin) and the South-West Atlantic (Angola and Brazil Basin) at spatial scales of 1000–3000 km, whereas all other communities were significantly differentiated from one another. It seems likely that multiple processes operate at the same time to shape communities of deep-sea kinetoplastids. Nevertheless, constant and homogenous environmental conditions over large spatial scales at abyssal depths, together with high dispersal capabilities of microbial eukaryotes, maintain best the results of statistically indistinguishable communities at larger spatial scales. PMID:22071346

  17. Statistical learning of temporal community structure in the hippocampus

    PubMed Central

    Schapiro, Anna C.; Turk-Browne, Nicholas B.; Norman, Kenneth A.; Botvinick, Matthew M.

    2015-01-01

    The hippocampus is involved in the learning and representation of temporal statistics, but little is understood about the kinds of statistics it can uncover. Prior studies have tested various forms of structure that can be learned by tracking the strength of transition probabilities between adjacent items in a sequence. We test whether the hippocampus can learn higher-order structure using sequences that have no variance in transition probability and instead exhibit temporal community structure. We find that the hippocampus is indeed sensitive to this form of structure, as revealed by its representations, activity dynamics, and connectivity with other regions. These findings suggest that the hippocampus is a sophisticated learner of environmental regularities, able to uncover higher-order structure that requires sensitivity to overlapping associations. PMID:26332666

  18. Community structure from spectral properties in complex networks

    NASA Astrophysics Data System (ADS)

    Servedio, V. D. P.; Colaiori, F.; Capocci, A.; Caldarelli, G.

    2005-06-01

    We analyze the spectral properties of complex networks focusing on their relation to the community structure, and develop an algorithm based on correlations among components of different eigenvectors. The algorithm applies to general weighted networks, and, in a suitably modified version, to the case of directed networks. Our method allows to correctly detect communities in sharply partitioned graphs, however it is useful to the analysis of more complex networks, without a well defined cluster structure, as social and information networks. As an example, we test the algorithm on a large scale data-set from a psychological experiment of free word association, where it proves to be successful both in clustering words, and in uncovering mental association patterns.

  19. Direct and indirect effects of high pCO2 on algal grazing by coral reef herbivores from the Gulf of Aqaba (Red Sea)

    NASA Astrophysics Data System (ADS)

    Borell, E. M.; Steinke, M.; Fine, M.

    2013-12-01

    Grazing on marine macroalgae is a key structuring process for coral reef communities. However, ocean acidification from rising atmospheric CO2 concentrations is predicted to adversely affect many marine animals, while seaweed communities may benefit and prosper. We tested how exposure to different pCO2 (400, 1,800 and 4,000 μatm) may affect grazing on the green alga Ulva lactuca by herbivorous fish and sea urchins from the coral reefs in the northern Gulf of Aqaba (Red Sea), either directly, by changing herbivore behaviour, or indirectly via changes in algal palatability. We also determined the effects of pCO2 on algal tissue concentrations of protein and the grazing-deterrent secondary metabolite dimethylsulfoniopropionate (DMSP). Grazing preferences and overall consumption were tested in a series of multiple-choice feeding experiments in the laboratory and in situ following exposure for 14 d (algae) and 28 d (herbivores). 4,000 μatm had a significant effect on the biochemical composition and palatability of U. lactuca. No effects were observed at 1,800 relative to 400 μatm (control). Exposure of U. lactuca to 4,000 μatm resulted in a significant decrease in protein and increase in DMSP concentration. This coincided with a reduced preference for these algae by the sea urchin Tripneustes gratilla and different herbivorous fish species in situ (Acanthuridae, Siganidae and Pomacanthidae). No feeding preferences were observed for the rabbitfish Siganus rivulatus under laboratory conditions. Exposure to elevated pCO2 had no direct effect on the overall algal consumption by T. gratilla and S. rivulatus. Our results show that CO2 has the potential to alter algal palatability to different herbivores which could have important implications for algal abundance and coral community structure. The fact that pCO2 effects were observed only at a pCO2 of 4,000 μatm, however, indicates that algal-grazer interactions may be resistant to predicted pCO2 concentrations in the

  20. A global perspective on marine photosynthetic picoeukaryote community structure

    PubMed Central

    Kirkham, Amy R; Lepère, Cécile; Jardillier, Ludwig E; Not, Fabrice; Bouman, Heather; Mead, Andrew; Scanlan, David J

    2013-01-01

    A central goal in ecology is to understand the factors affecting the temporal dynamics and spatial distribution of microorganisms and the underlying processes causing differences in community structure and composition. However, little is known in this respect for photosynthetic picoeukaryotes (PPEs), algae that are now recognised as major players in marine CO2 fixation. Here, we analysed dot blot hybridisation and cloning–sequencing data, using the plastid-encoded 16S rRNA gene, from seven research cruises that encompassed all four ocean biomes. We provide insights into global abundance, α- and β-diversity distribution and the environmental factors shaping PPE community structure and composition. At the class level, the most commonly encountered PPEs were Prymnesiophyceae and Chrysophyceae. These taxa displayed complementary distribution patterns, with peak abundances of Prymnesiophyceae and Chrysophyceae in waters of high (25:1) or low (12:1) nitrogen:phosphorus (N:P) ratio, respectively. Significant differences in phylogenetic composition of PPEs were demonstrated for higher taxonomic levels between ocean basins, using Unifrac analyses of clone library sequence data. Differences in composition were generally greater between basins (interbasins) than within a basin (intrabasin). These differences were primarily linked to taxonomic variation in the composition of Prymnesiophyceae and Prasinophyceae whereas Chrysophyceae were phylogenetically similar in all libraries. These data provide better knowledge of PPE community structure across the world ocean and are crucial in assessing their evolution and contribution to CO2 fixation, especially in the context of global climate change. PMID:23364354

  1. Algal biofuels: challenges and opportunities.

    PubMed

    Leite, Gustavo B; Abdelaziz, Ahmed E M; Hallenbeck, Patrick C

    2013-10-01

    Biodiesel production using microalgae is attractive in a number of respects. Here a number of pros and cons to using microalgae for biofuels production are reviewed. Algal cultivation can be carried out using non-arable land and non-potable water with simple nutrient supply. In addition, algal biomass productivities are much higher than those of vascular plants and the extractable content of lipids that can be usefully converted to biodiesel, triacylglycerols (TAGs) can be much higher than that of the oil seeds now used for first generation biodiesel. On the other hand, practical, cost-effective production of biofuels from microalgae requires that a number of obstacles be overcome. These include the development of low-cost, effective growth systems, efficient and energy saving harvesting techniques, and methods for oil extraction and conversion that are environmentally benign and cost-effective. Promising recent advances in these areas are highlighted. PMID:23499181

  2. Algal blooms and public health

    SciTech Connect

    Epstein, P.R. . Harvard Medical School)

    1993-06-01

    Alterations in coastal ecology are expanding the geographic extent, frequency, magnitude, and species complexity'' of algal blooms throughout the world, increasing the threat of fish and shellfish poisonings, anoxia in marine nurseries, and of cholera. The World Health Organization and members of the medical profession have described the potential health effects of global climate change. They warn of the consequences of increased ultraviolet-B (UV-B) rays and of warming: the possible damage to agriculture and nutrition, and the impact on habitats which may alter the distribution of vector-borne and water-based infectious diseases. Algal growth due to increased nitrogen (N) and phosphorus (P) and warming are already affecting marine microflora and aquatic plants; and there is now clear evidence that marine organisms are a reservoir for enteric pathogens. The pattern of cholera in the Western Hemisphere suggests that environmental changes have already begun to influence the epidemiology of this infectious disease. 106 refs.

  3. Kelp canopy facilitates understory algal assemblage via competitive release during early stages of secondary succession.

    PubMed

    Benes, Kylla M; Carpenter, Robert C

    2015-01-01

    Kelps are conspicuous foundation species in marine ecosystems that alter the composition of understory algal assemblages. While this may be due to changes in the competitive interactions between algal species, how kelp canopies mediate propagule supply and establishment success of understory algae is not well known. In Southern California, USA, Eisenia arborea forms dense kelp canopies in shallow subtidal environments and is associated with an understory dominated by red algal species. In canopy-free areas, however, the algal assemblage is comprised of mostly brown algal species. We used a combination of mensurative and manipulative experiments to test whether Eisenia facilitates the understory assemblage by reducing competition between these different types of algae by changes in biotic interactions and/or recruitment. Our results show Eisenia facilitates a red algal assemblage via inhibition of brown algal settlement into the canopy zone, allowing recruitment to occur by vegetative means rather than establishment of new individuals. In the canopy-free zone, however, high settlement and recruitment rates suggest competitive interactions shape the community there. These results demonstrate that foundation species alter the distribution and abundance of associated organisms by affecting not only interspecific interactions but also propagule supply and recruitment limitation. PMID:26236909

  4. Characteristics of turbulent boundary layer flow over algal biofilm

    NASA Astrophysics Data System (ADS)

    Murphy, Elizabeth; Barros, Julio; Schultz, Michael; Steppe, Cecily; Flack, Karen; Reidenbach, Matthew

    2015-11-01

    Algal biofilms are an important fouling community on ship hulls, with severe economic consequences due to drag-induced increases in fuel use and cleaning costs. Here, we characterize the boundary layer flow structure in turbulent flow over diatomaceous slime, a type of biofilm. Diatomaceous slime composed of three species of diatoms commonly found on ship hulls was grown on acrylic test plates under shear stress. The slime averages 1.6 mm in thickness and has a high density of streamers, which are flexible elongated growths with a length on the order of 1- 2 mm located at the top of the biofilm that interact with the flow. Fouled acrylic plates were placed in a water tunnel facility specialized for detailed turbulent boundary layer measurements. High resolution Particle Image Velocimetry (PIV) data are analyzed for mean velocity profile as well as local turbulent stresses and turbulent kinetic energy (TKE) production, dissipation and transport. Quadrant analysis is used to characterize the impact of the instantaneous events of Reynolds shear stress (RSS) in the flow. To investigate the coherence of the large-scale motion in the flow two-point correlation analysis is employed. Funding provided by the Office of Naval Research and the National Science Foundation.

  5. Diatom community structure on in-service cruise ship hulls.

    PubMed

    Hunsucker, Kelli Zargiel; Koka, Abhishek; Lund, Geir; Swain, Geoffrey

    2014-10-01

    Diatoms are an important component of marine biofilms found on ship hulls. However, there are only a few published studies that describe the presence and abundance of diatoms on ships, and none that relate to modern ship hull coatings. This study investigated the diatom community structure on two in-service cruise ships with the same cruise cycles, one coated with an antifouling (AF) system (copper self-polishing copolymer) and the other coated with a silicone fouling-release (FR) system. Biofilm samples were collected during dry docking from representative areas of the ship and these provided information on the horizontal and vertical zonation of the hull, and intact and damaged coating and niche areas. Diatoms from the genera Achnanthes, Amphora and Navicula were the most common, regardless of horizontal ship zonation and coating type. Other genera were abundant, but their presence was more dependent on the ship zonation and coating type. Samples collected from damaged areas of the hull coating had a similar community composition to undamaged areas, but with higher diatom abundance. Diatom fouling on the niche areas differed from that of the surrounding ship hull and paralleled previous studies that investigated differences in diatom community structure on static and dynamically exposed coatings; niche areas were similar to static immersion and the hull to dynamic immersion. Additionally, diatom richness was greater on the ship with the FR coating, including the identification of several new genera to the biofouling literature, viz. Lampriscus and Thalassiophysa. These results are the first to describe diatom community composition on in-service ship hulls coated with a FR system. This class of coatings appears to have a larger diatom community compared to copper-based AF systems, with new diatom genera that have the ability to stick to ship hulls and withstand hydrodynamic forces, thus creating the potential for new problematic species in the biofilm. PMID

  6. Oceanographic structure drives the assembly processes of microbial eukaryotic communities

    PubMed Central

    Monier, Adam; Comte, Jérôme; Babin, Marcel; Forest, Alexandre; Matsuoka, Atsushi; Lovejoy, Connie

    2015-01-01

    Arctic Ocean microbial eukaryote phytoplankton form subsurface chlorophyll maximum (SCM), where much of the annual summer production occurs. This SCM is particularly persistent in the Western Arctic Ocean, which is strongly salinity stratified. The recent loss of multiyear sea ice and increased particulate-rich river discharge in the Arctic Ocean results in a greater volume of fresher water that may displace nutrient-rich saltier waters to deeper depths and decrease light penetration in areas affected by river discharge. Here, we surveyed microbial eukaryotic assemblages in the surface waters, and within and below the SCM. In most samples, we detected the pronounced SCM that usually occurs at the interface of the upper mixed layer and Pacific Summer Water (PSW). Poorly developed SCM was seen under two conditions, one above PSW and associated with a downwelling eddy, and the second in a region influenced by the Mackenzie River plume. Four phylogenetically distinct communities were identified: surface, pronounced SCM, weak SCM and a deeper community just below the SCM. Distance–decay relationships and phylogenetic structure suggested distinct ecological processes operating within these communities. In the pronounced SCM, picophytoplanktons were prevalent and community assembly was attributed to water mass history. In contrast, environmental filtering impacted the composition of the weak SCM communities, where heterotrophic Picozoa were more numerous. These results imply that displacement of Pacific waters to greater depth and increased terrigenous input may act as a control on SCM development and result in lower net summer primary production with a more heterotroph dominated eukaryotic microbial community. PMID:25325383

  7. Oceanographic structure drives the assembly processes of microbial eukaryotic communities.

    PubMed

    Monier, Adam; Comte, Jérôme; Babin, Marcel; Forest, Alexandre; Matsuoka, Atsushi; Lovejoy, Connie

    2015-04-01

    Arctic Ocean microbial eukaryote phytoplankton form subsurface chlorophyll maximum (SCM), where much of the annual summer production occurs. This SCM is particularly persistent in the Western Arctic Ocean, which is strongly salinity stratified. The recent loss of multiyear sea ice and increased particulate-rich river discharge in the Arctic Ocean results in a greater volume of fresher water that may displace nutrient-rich saltier waters to deeper depths and decrease light penetration in areas affected by river discharge. Here, we surveyed microbial eukaryotic assemblages in the surface waters, and within and below the SCM. In most samples, we detected the pronounced SCM that usually occurs at the interface of the upper mixed layer and Pacific Summer Water (PSW). Poorly developed SCM was seen under two conditions, one above PSW and associated with a downwelling eddy, and the second in a region influenced by the Mackenzie River plume. Four phylogenetically distinct communities were identified: surface, pronounced SCM, weak SCM and a deeper community just below the SCM. Distance-decay relationships and phylogenetic structure suggested distinct ecological processes operating within these communities. In the pronounced SCM, picophytoplanktons were prevalent and community assembly was attributed to water mass history. In contrast, environmental filtering impacted the composition of the weak SCM communities, where heterotrophic Picozoa were more numerous. These results imply that displacement of Pacific waters to greater depth and increased terrigenous input may act as a control on SCM development and result in lower net summer primary production with a more heterotroph dominated eukaryotic microbial community. PMID:25325383

  8. Bacterial community structure in aquifers corresponds to stratigraphy

    NASA Astrophysics Data System (ADS)

    Beyer, Andrea; Möller, Silke; Neumann, Stefan; Burow, Katja; Gutmann, Falko; Lindner, Julia; Müsse, Steffen; Kothe, Erika; Büchel, Georg

    2014-05-01

    So far, groundwater microbiology with respect to different host rocks has not been well described in the literature. However, factors influencing the communities would be of interest to provide a tool for mapping groundwater paths. The Thuringian Basin (Germany) studied here, contains formations of the Permian (Zechstein) and also Triassic period of Buntsandstein, Muschelkalk and Keuper, all of which can be found to crop out at the surface in different regions. We analyzed the bacterial community of nine natural springs and sixteen groundwater wells of the respective rock formations as well as core material from the Zechstein salts. For that we sampled in a mine 3 differnet salt rock samples (carnallitite, halite and sylvinitite). To validate the different approaches, similar rock formations were compared and a consistent microbial community for Buntsandstein could be verified. Similary, for Zechstein, the presence of halophiles was seen with cultivation, isolation directly from the rock material and also in groundwater with DNA-dependent approaches. A higher overlap between sandstone- and limestone-derived communities was visible as if compared to the salt formations. Principal component analysis confirmed formation specific patterns for Muschelkalk, Buntsandstein and Zechstein for the bacterial taxa present, with some overlaps. Bacilli and Gammaproteobacteria were the major groups, with the genera Pseudomonas, Marinomonas, Bacillus, Marinobacter and Pseudoalteromonas representing the communities. The bacteria are well adapted to their respective environment with survival strategies including a wide range of salinity which makes them suitable as tracers for fluid movement below the ground. The results indicate the usefulness and robustness of the approach taken here to investigate aquifer community structures in dependence of the stratigraphy of the groundwater reservoir.

  9. Making the links between community structure and individual well-being: community quality of life in Riverdale, Toronto, Canada.

    PubMed

    Raphael, D; Renwick, R; Brown, I; Steinmetz, B; Sehdev, H; Phillips, S

    2001-09-01

    An inquiry into community quality of life was carried out within a framework that recognizes the complex relationship between community structures and individual well-being. Through use of focus groups and key informant interviews, community members, service providers, and elected representatives in a Toronto community considered aspects of their community that affected quality of life. Community members identified strengths of access to amenities, caring and concerned people, community agencies, low-cost housing, and public transportation. Service providers and elected representatives recognized diversity, community agencies and resources, and presence of culturally relevant food stores and services as strengths. At one level, findings were consistent with emerging concepts of social capital. At another level, threats to the community were considered in relation to the hypothesized role neo-liberalism plays in weakening the welfare state. PMID:11439254

  10. Microbial Community Structure in the Rhizosphere of Rice Plants

    PubMed Central

    Breidenbach, Björn; Pump, Judith; Dumont, Marc G.

    2016-01-01

    The microbial community in the rhizosphere environment is critical for the health of land plants and the processing of soil organic matter. The objective of this study was to determine the extent to which rice plants shape the microbial community in rice field soil over the course of a growing season. Rice (Oryza sativa) was cultivated under greenhouse conditions in rice field soil from Vercelli, Italy and the microbial community in the rhizosphere of planted soil microcosms was characterized at four plant growth stages using quantitative PCR and 16S rRNA gene pyrotag analysis and compared to that of unplanted bulk soil. The abundances of 16S rRNA genes in the rice rhizosphere were on average twice that of unplanted bulk soil, indicating a stimulation of microbial growth in the rhizosphere. Soil environment type (i.e., rhizosphere versus bulk soil) had a greater effect on the community structure than did time (e.g., plant growth stage). Numerous phyla were affected by the presence of rice plants, but the strongest effects were observed for Gemmatimonadetes, Proteobacteria, and Verrucomicrobia. With respect to functional groups of microorganisms, potential iron reducers (e.g., Geobacter, Anaeromyxobacter) and fermenters (e.g., Clostridiaceae, Opitutaceae) were notably enriched in the rhizosphere environment. A Herbaspirillum species was always more abundant in the rhizosphere than bulk soil and was enriched in the rhizosphere during the early stage of plant growth. PMID:26793175

  11. Linking Microbial Community Structure to Function in Representative Simulated Systems

    PubMed Central

    Marcus, Ian M.; Wilder, Hailey A.; Quazi, Shanin J.

    2013-01-01

    Pathogenic bacteria are generally studied as a single strain under ideal growing conditions, although these conditions are not the norm in the environments in which pathogens typically proliferate. In this investigation, a representative microbial community along with Escherichia coli O157:H7, a model pathogen, was studied in three environments in which such a pathogen could be found: a human colon, a septic tank, and groundwater. Each of these systems was built in the lab in order to retain the physical/chemical and microbial complexity of the environments while maintaining control of the feed into the models. The microbial community in the colon was found to have a high percentage of bacteriodetes and firmicutes, while the septic tank and groundwater systems were composed mostly of proteobacteria. The introduction of E. coli O157:H7 into the simulated systems elicited a shift in the structures and phenotypic cell characteristics of the microbial communities. The fate and transport of the microbial community with E. coli O157:H7 were found to be significantly different from those of E. coli O157:H7 studied as a single isolate, suggesting that the behavior of the organism in the environment was different from that previously conceived. The findings in this study clearly suggest that to gain insight into the fate of pathogens, cells should be grown and analyzed under conditions simulating those of the environment in which the pathogens are present. PMID:23396331

  12. Spatial analysis of early successional, temperate forest community structure

    NASA Astrophysics Data System (ADS)

    Walker, R. H.; Williams, C. A.; MacLean, R. G.; Epstein, H. E.; Vanderhoof, M. K.

    2013-12-01

    The global importance of sequestration of carbon by temperate forests makes characterizing the regrowth of these forests post-disturbance both ecologically and economically important. High intensity disturbances, such as logging, result in substantial alteration of community composition post-disturbance, creating the potential for alterations to the cycling of carbon, water, and nutrients in the ecosystem. Because logging pressure in New England continues to increase, understanding how forest ecosystems in this region respond to disturbance is crucial. This study aims to characterize interspecies interactions within New England forests by identifying synchronous and asynchronous colocation of species following a disturbance. To accomplish this, line-intercept surveys of vegetation were conducted in a clearcut forest stand located within the Harvard Forest LTER site. Survey data collected two (2010) and five (2013) years post-clearcut were analyzed using a one-dimensional Ripley's K. From 2010 to 2013, an increase in the number of interspecies relationships was observed, indicating the development of community structure. Additionally, the analysis found an increase in total vegetative cover from 2010 to 2013, and also found the majority of observed interspecies relationships to be asynchronous relationships. Together, these results imply an increase in resource competition that had the potential to drive the increase in community structure. Specifically, an increase in community structure led to the development of three distinct sub-communities: homogenous fern, tree seedling canopy over ground cover, and shrub dominated. This creates a patchy landscape in the early successional forest that allows for high species diversity (Shannon's H = 2.455). Based on the results of the Ripley's K analyses, species demonstrated definite patterns of synchronicity and asynchronicity based on both specific species interactions as well as functional group interactions. These

  13. Securing the Future: Retention Models in Community Colleges--Study of Community College Structures for Student Success (SCCSSS)

    ERIC Educational Resources Information Center

    College Board Advocacy & Policy Center, 2012

    2012-01-01

    The Study of Community College Structures for Student Success (SCCSSS) was launched in 2010 with three goals at its center: (1) To explore a set of promising institutional practices and organizational structures identified through theory and research as having the potential to support community college student success; (2) To present a synthesized…

  14. Fungal endophyte communities reflect environmental structuring across a Hawaiian landscape.

    PubMed

    Zimmerman, Naupaka B; Vitousek, Peter M

    2012-08-01

    We surveyed endophytic fungal communities in leaves of a single tree species (Metrosideros polymorpha) across wide environmental gradients (500-5,500 mm of rain/y; 10-22 °C mean annual temperature) spanning short geographic distances on Mauna Loa Volcano, Hawai'i. Using barcoded amplicon pyrosequencing at 13 sites (10 trees/site; 10 leaves/tree), we found very high levels of diversity within sites (a mean of 551 ± 134 taxonomic units per site). However, among-site diversity contributed even more than did within-site diversity to the overall richness of more than 4,200 taxonomic units observed in M. polymorpha, and this among-site variation in endophyte community composition correlated strongly with temperature and rainfall. These results are consistent with suggestions that foliar endophytic fungi are hyperdiverse. They further suggest that microbial diversity may be even greater than has been assumed and that broad-scale environmental controls such as temperature and rainfall can structure eukaryotic microbial diversity. Appropriately constrained study systems across strong environmental gradients present a useful means to understand the environmental factors that structure the diversity of microbial communities. PMID:22837398

  15. Fungal endophyte communities reflect environmental structuring across a Hawaiian landscape

    PubMed Central

    Zimmerman, Naupaka B.; Vitousek, Peter M.

    2012-01-01

    We surveyed endophytic fungal communities in leaves of a single tree species (Metrosideros polymorpha) across wide environmental gradients (500–5,500 mm of rain/y; 10–22 °C mean annual temperature) spanning short geographic distances on Mauna Loa Volcano, Hawai’i. Using barcoded amplicon pyrosequencing at 13 sites (10 trees/site; 10 leaves/tree), we found very high levels of diversity within sites (a mean of 551 ± 134 taxonomic units per site). However, among-site diversity contributed even more than did within-site diversity to the overall richness of more than 4,200 taxonomic units observed in M. polymorpha, and this among-site variation in endophyte community composition correlated strongly with temperature and rainfall. These results are consistent with suggestions that foliar endophytic fungi are hyperdiverse. They further suggest that microbial diversity may be even greater than has been assumed and that broad-scale environmental controls such as temperature and rainfall can structure eukaryotic microbial diversity. Appropriately constrained study systems across strong environmental gradients present a useful means to understand the environmental factors that structure the diversity of microbial communities. PMID:22837398

  16. Combined effect of predatory zooplankton and allelopathic aquatic macrophytes on algal suppression.

    PubMed

    Zuo, Shengpeng; Wan, Kun; Ma, Sumin

    2015-01-01

    The present study evaluated the combined effects of four typical predatory zooplankton and allelopathic aquatic macrophytes on algal control in a microcosm system. It would determine the effects of diverse species and biological restoration on the growth of harmful water-bloom microalgae in great lakes polluted by excess nutrients. It was found that the mixtures of each zooplankton and the floating plant Nymphoides peltatum had stronger inhibitory effects on harmful water-bloom microalgae than the individual species in clean or eutrophic water bodies. In addition, a community of four zooplankton types had a synergistic effect on algal inhibition. Algal suppression by the zooplankton community was enhanced significantly when the macrophyte was co-cultured in the microcosm. Furthermore, Chlorella pyrenoidosa was more susceptible than Microcystis aeruginosa when exposed to grazing by zooplankton and the allelopathic potential of the macrophyte. Algal inhibition was also weaker in eutrophic conditions compared with the control. These findings indicate that diverse species may enhance algal inhibition. Therefore, it is necessary to restore biological diversity and rebuild an ecologically balanced food chain or web to facilitate the control of harmful algal blooms in eutrophic lakes. PMID:25409583

  17. Robust detection of dynamic community structure in networks

    NASA Astrophysics Data System (ADS)

    Bassett, Danielle S.; Porter, Mason A.; Wymbs, Nicholas F.; Grafton, Scott T.; Carlson, Jean M.; Mucha, Peter J.

    2013-03-01

    We describe techniques for the robust detection of community structure in some classes of time-dependent networks. Specifically, we consider the use of statistical null models for facilitating the principled identification of structural modules in semi-decomposable systems. Null models play an important role both in the optimization of quality functions such as modularity and in the subsequent assessment of the statistical validity of identified community structure. We examine the sensitivity of such methods to model parameters and show how comparisons to null models can help identify system scales. By considering a large number of optimizations, we quantify the variance of network diagnostics over optimizations ("optimization variance") and over randomizations of network structure ("randomization variance"). Because the modularity quality function typically has a large number of nearly degenerate local optima for networks constructed using real data, we develop a method to construct representative partitions that uses a null model to correct for statistical noise in sets of partitions. To illustrate our results, we employ ensembles of time-dependent networks extracted from both nonlinear oscillators and empirical neuroscience data.

  18. Robust detection of dynamic community structure in networks.

    PubMed

    Bassett, Danielle S; Porter, Mason A; Wymbs, Nicholas F; Grafton, Scott T; Carlson, Jean M; Mucha, Peter J

    2013-03-01

    We describe techniques for the robust detection of community structure in some classes of time-dependent networks. Specifically, we consider the use of statistical null models for facilitating the principled identification of structural modules in semi-decomposable systems. Null models play an important role both in the optimization of quality functions such as modularity and in the subsequent assessment of the statistical validity of identified community structure. We examine the sensitivity of such methods to model parameters and show how comparisons to null models can help identify system scales. By considering a large number of optimizations, we quantify the variance of network diagnostics over optimizations ("optimization variance") and over randomizations of network structure ("randomization variance"). Because the modularity quality function typically has a large number of nearly degenerate local optima for networks constructed using real data, we develop a method to construct representative partitions that uses a null model to correct for statistical noise in sets of partitions. To illustrate our results, we employ ensembles of time-dependent networks extracted from both nonlinear oscillators and empirical neuroscience data. PMID:23556979

  19. The Interplay between Environmental Filtering and Spatial Processes in Structuring Communities: The Case of Neotropical Snake Communities

    PubMed Central

    Cavalheri, Hamanda; Both, Camila; Martins, Marcio

    2015-01-01

    Both habitat filters and spatial processes can influence community structure. Space alone affects species immigration from the regional species pool, whereas habitat filters affect species distribution and inter-specific interactions. This study aimed to understand how the interplay between environmental and geographical processes influenced the structure of Neotropical snake communities in different habitat types. We selected six studies that sampled snakes in forests, four conducted in savannas and two in grasslands (the latter two are grouped in a non-forest category). We used the net relatedness and nearest taxon indices to assess phylogenetic structure within forest and non-forest areas. We also used the phylogenetic fuzzy-weighting algorithm to characterize phylogenetic structure across communities and the relation of phylogenetic composition patterns to habitat type, structure, and latitude. Finally, we tested for morphological trait convergence and phylogenetic niche conservatism using four forest and four non-forest areas for which morphological data were available. Community phylogenetic composition changed across forest and non-forest areas suggesting that environmental filtering influences community structure. Species traits were affected by habitat type, indicating convergence at the metacommunity level. Tail length, robustness, and number of ventral scales maximized community convergence among forest and non-forest areas. The observed patterns suggested environmental filtering, indicating that less vertically structured habitats represent a strong filter. Despite the fact that phylogenetic structure was not detected individually for each community, we observed a trend towards communities composed by more closely related species in higher latitudes and more overdispersed compositions in lower latitudes. Such pattern suggests that the limited distribution of major snake lineages constrained species distributions. Structure indices for each community

  20. Selective consumption and metabolic allocation of terrestrial and algal carbon determine allochthony in lake bacteria.

    PubMed

    Guillemette, François; Leigh McCallister, S; Del Giorgio, Paul A

    2016-06-01

    Here we explore strategies of resource utilization and allocation of algal versus terrestrially derived carbon (C) by lake bacterioplankton. We quantified the consumption of terrestrial and algal dissolved organic carbon, and the subsequent allocation of these pools to bacterial growth and respiration, based on the δ(13)C isotopic signatures of bacterial biomass and respiratory carbon dioxide (CO2). Our results confirm that bacterial communities preferentially remove algal C from the terrestrially dominated organic C pool of lakes, but contrary to current assumptions, selectively allocate this autochthonous substrate to respiration, whereas terrestrial C was preferentially allocated to biosynthesis. The results provide further evidence of a mechanism whereby inputs of labile, algal-derived organic C may stimulate the incorporation of a more recalcitrant, terrestrial C pool. This mechanism resulted in a counterintuitive pattern of high and relatively constant levels of allochthony (~76%) in bacterial biomass across lakes that otherwise differ greatly in productivity and external inputs. PMID:26623544

  1. Air pollutant production by algal cell cultures

    NASA Technical Reports Server (NTRS)

    Fong, F.; Funkhouser, E. A.

    1982-01-01

    The production of phytotoxic air pollutants by cultures of Chlorella vulgaris and Euglena gracilis is considered. Algal and plant culture systems, a fumigation system, and ethylene, ethane, cyanide, and nitrogen oxides assays are discussed. Bean, tobacco, mustard green, cantaloupe and wheat plants all showed injury when fumigated with algal gases for 4 hours. Only coleus plants showed any resistance to the gases. It is found that a closed or recycled air effluent system does not produce plant injury from algal air pollutants.

  2. Spanning tree separation reveals community structure in networks

    NASA Astrophysics Data System (ADS)

    Kim, Jongkwang; Wilhelm, Thomas

    2013-03-01

    We present a simple, intuitive, and effective approach for network clustering. It is based on basic concepts of linear algebra such as efficient calculation of spanning trees, and can be implemented in a few lines of code. We introduce the node separation measure spanning tree separation (STS) and the corresponding graph distance measure spanning tree vector similarity distance (STVSD). We demonstrate that the STS is a link salience measure able to identify the backbone of networks. The STVSD is used to reveal the hierarchical community structure of networks. We show that it, together with the clustering quality measure partition density, is on a par with the best graph or network clustering methods known, in terms of both quality and efficiency. In perspective, we note that our approach could also handle weighted and directed networks and could be used for identification of overlapping communities.

  3. Benthic infaunal community structuring in an acidified tropical estuarine system

    PubMed Central

    2014-01-01

    Background Recent studies suggest that increasing ocean acidification (OA) should have strong direct and indirect influences on marine invertebrates. While most theory and application for OA is based on relatively physically-stable oceanic ecological systems, less is known about the effects of acidification on nearshore and estuarine systems. Here, we investigated the structuring of a benthic infaunal community in a tropical estuarine system, along a steep salinity and pH gradient, arising largely from acid-sulphate groundwater inflows (Sungai Brunei Estuary, Borneo, July 2011- June 2012). Results Preliminary data indicate that sediment pore-water salinity (range: 8.07 - 29.6 psu) declined towards the mainland in correspondence with the above-sediment estuarine water salinity (range: 3.58 – 31.2 psu), whereas the pore-water pH (range: 6.47- 7.72) was generally lower and less variable than the estuarine water pH (range: 5.78- 8.3), along the estuary. Of the thirty six species (taxa) recorded, the polychaetes Neanthes sp., Onuphis conchylega, Nereididae sp. and the amphipod Corophiidae sp., were numerically dominant. Calcified microcrustaceans (e.g., Cyclopoida sp. and Corophiidae sp.) were abundant at all stations and there was no clear distinction in distribution pattern along the estuarine between calcified and non-calcified groups. Species richness increased seawards, though abundance (density) showed no distinct directional trend. Diversity indices were generally positively correlated (Spearman’s rank correlation) with salinity and pH (p <0.05) and negatively with clay and organic matter, except for evenness values (p >0.05). Three faunistic assemblages were distinguished: (1) nereid-cyclopoid-sabellid, (2) corophiid-capitellid and (3) onuphid- nereid-capitellid. These respectively associated with lower salinity/pH and a muddy bottom, low salinity/pH and a sandy bottom, and high salinity/pH and a sandy bottom. However, CCA suggested that species distribution

  4. Vertical structure of the phytoplankton community associated with a coastal plume in the Gulf of Mexico

    USGS Publications Warehouse

    Wawrik, B.; Paul, J.H.; Campbell, L.; Griffin, D.; Houchin, L.; Fuentes-Ortega, A.; Muller-Karger, F.

    2003-01-01

    Low salinity plumes of coastal origin are occasionally found far offshore, where they display a distinct color signature detectable by satellites. The impact of such plumes on carbon fixation and phytoplankton community structure in vertical profiles and on basin wide scales is poorly understood. On a research cruise in June 1999, ocean-color satellite-images (Sea-viewing Wide Field-of-view Sensor, SeaWiFS) were used in locating a Mississippi River plume in the eastern Gulf of Mexico. Profiles sampled within and outside of the plume were analyzed using flow cytometry, HPLC pigment analysis and primary production using 14C incorporation. Additionally, RubisCO large subunit (rbcL) gene expression was measured by hybridization of extracted RNA using 3 full-length RNA gene probes specific for individual phytoplankton clades. We also used a combination of RT-PCR/PCR and TA cloning in order to generate cDNA and DNA rbcL clone libraries from samples taken in the plume. Primary productivity was greatest in the low salinity surface layer of the plume. The plume was also associated with high Synechococcus counts and a strong peak in Form IA rbcL expression. Form IB rbcL (green algal) mRNA was abundant at the subsurface chlorophyll maximum (SCM), whereas Form ID rbcL (chromophytic) expression showed little vertical structure. Phylogenetic analysis of cDNA libraries demonstrated the presence of Form IA rbcL Synechococcus phylotypes in the plume. Below the plume, 2 spatially separated and genetically distinct rbcL clades of Prochlorococcus were observed. This indicated the presence of the high- and low-light adapted clades of Prochlorococcus. A large and very diverse clade of Prymnesiophytes was distributed throughout the water column, whereas a clade of closely related prasinophytes may have dominated at the SCM. These data indicate that the Mississippi river plume may dramatically alter the surface picoplankton composition of the Gulf of Mexico, with Synechococcus displacing

  5. Factors Affecting Trophic Control of Community Structure and Ecosystem Functioning in Experimental Mesocosms of Seagrass (Zostera marina L.)

    NASA Astrophysics Data System (ADS)

    Lefcheck, J.; Duffy, J.

    2008-12-01

    Nutrient loading of coastal and estuarine waters threatens seagrass communities by promoting the growth of micro- and macroalgae, which then reduce the availability of light and nutrients. However, populations of invertebrate mesograzers are able to mitigate the negative impact of eutrophication through top-down control. We performed a factorial mesocosm experiment to examine the interactive relationships between light, nutrients, and mesograzer presence in structuring experimental ecosystems of eelgrass (Zostera marina). We found that mesograzer presence strongly reduced epiphytic algal biomass in every case, which remains consistent with previous mesocosm studies. We also observed a synergistic light-by-nutrient interaction that enhanced both epiphyte biomass and mesograzer abundance. The timing of this relationship is suggestive of weaker bottom-up control. Unlike previous studies, we found that light alone rarely affected either epiphyte biomass or mesograzer abundance. We believe that this result may be due to a combination of macroalgal shading and persistent grazing. Further processing of primary and secondary producer biomasses and elemental ratios, as well as the completion of feeding assays to gauge mesograzer feeding rates on different types of algae, will serve to reinforce these conclusions and to better define the relationship between these factors.

  6. Water availability controls on community structure of an ephemeral meltwater stream ecosystem in the McMurdo Dry Valleys

    NASA Astrophysics Data System (ADS)

    McKnight, D. M.; Simmons, B.; Stanish, L.

    2009-05-01

    The McMurdo Dry Valleys of Antarctica contain many glacial meltwater streams that flow during the summer into lakes on the valley floors. Many streams have thriving cyanobacterial mats that are freeze-dried in winter and begin photosynthesis when flow arrives. We studied the community structure in a formerly abandoned channel, which was reactivated by a flow diversion in 1994. Cyanobacterial mats became abundant in the reactivated channel within a week and have remained evident even through cold, low flow summers. We recently compared the abundance and species distribution of invertebrates and diatoms in the cyanobacterial mats and in hyporheic zone during cold (low flow) and warm (high flow) summers. During the warm summer, there were sites where the invertebrate abundance was greater in the mats than in the underlying hyporheic sediments. In contrast, during the cold summer the invertebrate biomass was lower in the mats than in the hyporheic sediments. These findings suggest that the optimal micro-habitat for invertebrates in these mats and sediments is partially driven by ephemeral stream hydrology. This limitation on potential invertebrate grazers (which are important nutrient transformers) may account for the accumulation of algal biomass and subsequent nutrient immobilization in the mats over many summers.

  7. A shift in the dominant toxin-producing algal species in central California alters phycotoxins in food webs

    USGS Publications Warehouse

    Jester, R.; Lefebvre, K.; Langlois, G.; Vigilant, V.; Baugh, K.; Silver, M.W.

    2009-01-01

    In California, the toxic algal species of primary concern are the dinoflagellate Alexandrium catenella and members of the pennate diatom genus Pseudo-nitzschia, both producers of potent neurotoxins that are capable of sickening and killing marine life and humans. During the summer of 2004 in Monterey Bay, we observed a change in the taxonomic structure of the phytoplankton community-the typically diatom-dominated community shifted to a red tide, dinoflagellate-dominated community. Here we use a 6-year time series (2000-2006) to show how the abundance of the dominant harmful algal bloom (HAB) species in the Bay up to that point, Pseudo-nitzschia, significantly declined during the dinoflagellate-dominated interval, while two genera of toxic dinoflagellates, Alexandrium and Dinophysis, became the predominant toxin producers. This change represents a shift from a genus of toxin producers that typically dominates the community during a toxic bloom, to HAB taxa that are generally only minor components of the community in a toxic event. This change in the local HAB species was also reflected in the toxins present in higher trophic levels. Despite the small contribution of A. catenella to the overall phytoplankton community, the increase in the presence of this species in Monterey Bay was associated with an increase in the presence of paralytic shellfish poisoning (PSP) toxins in sentinel shellfish and clupeoid fish. This report provides the first evidence that PSP toxins are present in California's pelagic food web, as PSP toxins were detected in both northern anchovies (Engraulis mordax) and Pacific sardines (Sardinops sagax). Another interesting observation from our data is the co-occurrence of DA and PSP toxins in both planktivorous fish and sentinel shellfish. We also provide evidence, based on the statewide biotoxin monitoring program, that this increase in the frequency and abundance of PSP events related to A. catenella occurred not just in Monterey Bay, but also

  8. Comparing new and conventional methods to estimate benthic algal biomass and composition in freshwaters.

    PubMed

    Kahlert, Maria; McKie, Brendan G

    2014-11-01

    We compared conventional microscope-based methods for quantifying biomass and community composition of stream benthic algae with output obtained for these parameters from a new instrument (the BenthoTorch), which measures fluorescence of algal pigments in situ. Benthic algae were studied in 24 subarctic oligotrophic (1.7-26.9, median 7.2 μg total phosphorus L(-1)) streams in Northern Sweden. Readings for biomass of the total algal mat, quantified as chlorophyll a, did not differ significantly between the BenthoTorch (median 0.52 μg chlorophyll a cm(-2)) and the conventional method (median 0.53 μg chlorophyll a cm(-2)). However, quantification of community composition of the benthic algal mat obtained using the BenthoTorch did not match those obtained from conventional methods. The BenthoTorch indicated a dominance of diatoms, whereas microscope observations showed a fairly even distribution between diatoms, blue-green algae (mostly nitrogen-fixing) and green algae (mostly large filamentous), and also detected substantial biovolumes of red algae in some streams. These results most likely reflect differences in the exact parameters quantified by the two methods, as the BenthoTorch does not account for variability in cell size and the presence of non-chlorophyll bearing biomass in estimating the proportion of different algal groups, and does not distinguish red algal chlorophyll from that of other algal groups. Our findings suggest that the BenthoTorch has utility in quantifying biomass expressed as μg chlorophyll a cm(-2), but its output for the relative contribution of different algal groups to benthic algal biomass should be used with caution. PMID:25277172

  9. Distributional shifts in size structure of phytoplankton community

    NASA Astrophysics Data System (ADS)

    Waga, H.; Hirawake, T.; Fujiwara, A.; Nishino, S.; Kikuchi, T.; Suzuki, K.; Takao, S.

    2015-12-01

    Increased understanding on how marine species shift their distribution is required for effective conservation of fishery resources under climate change. Previous studies have often predicted distributional shifts of fish using satellite derived sea surface temperature (SST). However, SST may not fully represent the changes in species distribution through food web structure and as such this remains an open issue due to lack of ecological perspective on energy transfer process in the earlier studies. One of the most important factors in ecosystem is composition of phytoplankton community, and its size structure determines energy flow efficiency from base to higher trophic levels. To elucidate spatiotemporal variation in phytoplankton size structure, chlorophyll-a size distribution (CSD) algorithm was developed using spectral variance of phytoplankton absorption coefficient through principal component analysis. Slope of CSD (CSD slope) indicates size structure of phytoplankton community where, strong and weak magnitudes of CSD slope indicate smaller and larger phytoplankton structure, respectively. Shifts in CSD slope and SST were derived as the ratio of temporal trend over the 12-year period (2003-2014) to 2-dimensional spatial gradient and the resulting global median velocity of CSD slope and SST were 0.361 and 0.733 km year-1, respectively. In addition, the velocity of CSD slope monotonically increases with increasing latitude, while relatively complex latitudinal pattern for SST emerged. Moreover, angle of shifts suggest that species are required to shift their distribution toward not limited to simple pole-ward migration, and some regions exhibit opposite direction between the velocity of CSD slope and SST. These findings further imply that combined phytoplankton size structure and SST may contribute for more accurate prediction of species distribution shifts relative to existing studies which only considering variations in thermal niches.

  10. Bacterial Community Structure Response to Petroleum Concentration in Groundwater

    NASA Astrophysics Data System (ADS)

    Kitts, C. L.; Wrighton, K. C.; Phillips, W. A.; Cano, R. J.; Lundegard, P. D.

    2004-12-01

    This study characterized the bacterial community present in groundwater samples from the Guadalupe Dunes Restoration Project on the central California coast. The purpose of the study was to determine the changes in bacterial community structure and function in response to variations in the concentration of dissolved phase total petroleum hydrocarbons (TPH) in groundwater plumes at the site. For the purpose of this study groundwater samples were collected at varying distance from TPH source zones in 10 different plumes. All samples were analyzed for ammonia, phosphate, TPH, methane, oxygen, carbon dioxide, nitrate, sulfate, and dissolved iron levels. Chemical analysis revealed that the groundwater chemistry varied between plumes and on a well-to-well basis within a plume. Principle component analyses (PCA) demonstrated that TPH degradation related parameters explained 28% of the variation in the groundwater chemistry. In addition to the physical and chemical analyses, four liters of each groundwater sample were filtered and bacterial DNA was isolated to determine the relationship between groundwater chemistry and bacterial community structure and function. Specific Polymerase Chain Reaction (PCR) primers were used to characterize populations of Eubacteria, and Archaea, as well as function genes for sulfate reducing, methanotrophic, and methanogenic bacteria. Terminal Restriction Fragment (TRF) Length Polymorphisms (or T-RFLP) were used to analyze community structure. Eubacterial and Archaeal groundwater communities were separated into distinct clusters which did not clearly reflect changes in groundwater chemical parameters unless individual plumes were analyzed separately. However, specific Eubacterial and Archaeal TRF peaks did correspond to known petroleum degrading organisms and methanogenic bacteria, respectively. Only one sample produced a positive result for the sulfite reductase gene (dsrAB), indicating that sulfate reduction may not be a dominant process at

  11. The CECAM Electronic Structure Library: community-driven development of software libraries for electronic structure simulations

    NASA Astrophysics Data System (ADS)

    Oliveira, Micael

    The CECAM Electronic Structure Library (ESL) is a community-driven effort to segregate shared pieces of software as libraries that could be contributed and used by the community. Besides allowing to share the burden of developing and maintaining complex pieces of software, these can also become a target for re-coding by software engineers as hardware evolves, ensuring that electronic structure codes remain at the forefront of HPC trends. In a series of workshops hosted at the CECAM HQ in Lausanne, the tools and infrastructure for the project were prepared, and the first contributions were included and made available online (http://esl.cecam.org). In this talk I will present the different aspects and aims of the ESL and how these can be useful for the electronic structure community.

  12. Food resource use by two territorial damselfish (Pomacentridae: Stegastes) on South-Western Atlantic algal-dominated reefs

    NASA Astrophysics Data System (ADS)

    Feitosa, João Lucas L.; Concentino, Adilma M.; Teixeira, Simone F.; Ferreira, Beatrice P.

    2012-05-01

    Damselfishes are a highly abundant group of reef fishes that are considered keystone species for structuring benthic communities on coral-dominated reefs. To assess how food is utilized by the damselfish species Stegastes fuscus and Stegastes variabilis living on algae-dominated coastal reefs, we evaluated the compositions of algal communities inside their territories and investigated their diets by analyzing their stomach contents. Jointed-calcareous algae were the most abundant morphological group inside the territories of both damselfish species (> 80%), and the biomass of these algae showed a positive linear relationship to all the other non-calcareous algae when grouped together (R² = 0.674; p < 0.001), suggesting that the former exerts a positive influence on the biomasses of species of non-calcareous algae by creating surfaces on which they can grow. Most of the diet of Stegastes spp. consisted of algal material (> 70%), but they also fed on invertebrates and detritus as accessory items (~ 15%). Algal material composed a consistent proportion of the items ingested by adults and juveniles of both damselfish species with diatoms being the most frequent item, followed by filamentous algae. A positive food selection for all macroalgae morphological groups was observed, except for jointed-calcareous algae (Ivlev's index). The most preferred macroalgae types were filamentous, with values close to + 1 for both damselfish species. Pianka's food overlap index was extremely high regardless of the damselfish species or their life phase and ANOSIM analyses also confirmed that there were essentially no differences between their diets. The present work is the first indication that damselfish may maintain territories dominated by highly unpalatable calcareous macroalgae that have herbivore-deterrent life strategies, although the complex branching structures of these macroalgae create suitable microhabitats for the growth of epiphytic species consumed by the damselfish.

  13. Stability of alginate-immobilized algal cells

    SciTech Connect

    Dainty, A.L.; Goulding, K.H.; Robinson, P.K.; Simpkins, I; Trevan, M.D.

    1986-01-01

    Investigations were carried out using immobilized Chlorella cells to determine the diameter, compressibility, tolerance to phosphate chelation, and ability to retain algal cells during incubation of various alginate beads. These physical bead-characteristics were affected by a variety of interactive factors, including multivalent cation type (hardening agent) and cell, cation, and alginate concentration, the latter exhibiting a predominant influence. The susceptibility of alginate beads to phosphate chelation involved a complex interaction of cation type, concentration, and pH of phosphate solution. A scale of response ranging from gel swelling to gel shrinking was observed for a range of conditions. However, stable Ca alginate beads were maintained in incubation media with a pH of 5.5 and a phosphate concentration of 5 micro M. A preliminary investigation into cell leakage from the beads illustrated the importance of maintaining a stable gel structure and limiting cell growth to reduce leakage.

  14. Analysis of community structure in networks of correlated data

    SciTech Connect

    Gomez, S.; Jensen, P.; Arenas, A.

    2008-12-25

    We present a reformulation of modularity that allows the analysis of the community structure in networks of correlated data. The new modularity preserves the probabilistic semantics of the original definition even when the network is directed, weighted, signed, and has self-loops. This is the most general condition one can find in the study of any network, in particular those defined from correlated data. We apply our results to a real network of correlated data between stores in the city of Lyon (France).

  15. Fast algorithm for detecting community structure in networks

    NASA Astrophysics Data System (ADS)

    Newman, M. E.

    2004-06-01

    Many networks display community structure—groups of vertices within which connections are dense but between which they are sparser—and sensitive computer algorithms have in recent years been developed for detecting this structure. These algorithms, however, are computationally demanding, which limits their application to small networks. Here we describe an algorithm which gives excellent results when tested on both computer-generated and real-world networks and is much faster, typically thousands of times faster, than previous algorithms. We give several example applications, including one to a collaboration network of more than 50 000 physicists.

  16. Visual Analysis of Complex Networks and Community Structure

    NASA Astrophysics Data System (ADS)

    Wu, Bin; Ye, Qi; Wang, Yi; Bi, Ran; Suo, Lijun; Hu, Deyong; Yang, Shengqi

    Many real-world domains can be represented as complex networks.A good visualization of a large and complex network is worth more than millions of words. Visual depictions of networks, which exploit human visual processing, are more prone to cognition of the structure of such complex networks than the computational representation. We star by briefly introducing some key technologies of network visualization, such as graph drawing algorithm and community discovery methods. The typical tools for network visualization are also reviewed. A newly developed software framework JSNVA for network visual analysis is introduced. Finally,the applications of JSNVA in bibliometric analysis and mobile call graph analysis are presented.

  17. Changes in the bacterial community structure in stored wormbed leachate.

    PubMed

    Romero-Tepal, Elda M; Contreras-Blancas, Eduardo; Navarro-Noya, Yendi E; Ruíz-Valdiviezo, Víctor M; Luna-Guido, Marco; Gutiérrez-Miceli, Federico A; Dendooven, Luc

    2014-01-01

    Organic wastes, such as cow manure, are often composted with earthworms (vermicomposting) while excess water is drained and collected. This wormbed leachate is nutrient-rich and it has been extensively used to fertilize plants. However, it is derived partially from a not yet finished compost process and could exhibit phytotoxicity or contain potentially hazardous microorganisms. The bacterial community in wormbed leachate derived from vermicomposting of cow manure was studied by pyrosequencing the 16S rRNA gene. The fresh wormbed leachate was rich in Mollicutes, particularly the genus Acholeplasma which contain phytopathogen species. The abundance of the Mollicutes decreased when the leachate was stored, while that of the Rhizobiales and the genus Pseudomonas increased. The bacterial communities changed rapidly in the leachate during storage. The changes in ammonium, nitrate and inorganic carbon content of the wormbed leachate when stored were correlated to changes in the bacterial community structure. It was found that storage of the wormbed leachate might be required before it can be applied to crops as large proportions of potentially plant pathogens were found in the fresh leachate. PMID:24577291

  18. Environmental factors influencing cyanobacteria community structure in Dongping Lake, China.

    PubMed

    Lu, Xuetang; Tian, Chang; Pei, Haiyan; Hu, Wenrong; Xie, Jun

    2013-11-01

    The present study was conducted to provide a detailed understanding of the variation in cyanobacterial communities of Dongping Lake, which is the final water volume adjusting and storing lake in the east route of the South-to-North Water Diversion Project in China. The spatial and temporal distribution of cyanobacteria was assessed from May 2010 to October 2012 based on monthly samples collected from three stations. Over the 30-month survey, 15 genera and 25 species of cyanobacteria were identified, with cyanobacterial abundance at each monitoring station ranging from undetected to 3.04x10(7) cells/L, average of 4.27x10(6) cells/L. The dominant cyanobacterial species were Pseudanabaena limnetica and Aphanizomenon issatschenkoi and not the usual bloom-forming genera such as Microcystis and Anabaena. Cyanobacterial community structure and water quality variables exhibited substantial changes over the period of survey. Redundancy analysis, Pearson correlations, and regression analysis were applied to analyze the relationships among the variables. The results suggested that temperature and chemical oxygen demand were key drivers of the cyanobacterial community composition in Dongping Lake. In addition, the concentration of inorganic nitrogen in the lake had a profound effect on the cyanobacterial abundance as a non-limiting factor in warm periods. PMID:24552047

  19. Experimental warming effects on the bacterial community structure and diversity

    NASA Astrophysics Data System (ADS)

    Kim, W.; Han, S.; Adams, J.; Son, Y.

    2014-12-01

    The objective of this study is to investigate the responses of soil bacterial community to future temperature increase by conducting open-field warming experiment. We conducted an open-field experimental warming system using infra-red heater in 2011 and regulated the temperature of warmed plots by 3oC higher than that of control plots constantly. The seeds of Pinus densiflora, Abies holophylla, Abies koreana, Betula costata, Quercus variabilis, Fraxinus rhynchophylla, and Zelkova serrata were planted in each 1 m × 1 m plot (n=3) in April, 2012. We collected soil samples from the rhizosphere of 7 tree species. DNA was extracted and PCR-amplified for the bacterial 16S gene targeting V1-V3 region. The paired-end sequencing was performed at Beijing Genome Institute (BGI, Hong Kong, China) using 2× 100 bp Hiseq2000 (Illumina). This study aimed to answer the following prediction/hypothesis: 1) Experimental warming will change the structure of soil bacterial community, 2) There will be distinct 'indicator group' which response to warming treatment relatively more sensitive than other groups. 3) Warming treatment will enhance the microbial activity in terms of soil respiration. 4) The rhizoplane bacterial communities for each of 7 tree species will show different response pattern to warming treatment. Since the sequence data does not arrive before the submission deadline, therefore, we would like to present the results and discussions on December 2014, AGU Fall Meeting.

  20. Prey bacteria shape the community structure of their predators

    PubMed Central

    Chen, Huan; Athar, Rana; Zheng, Guili; Williams, Henry N

    2011-01-01

    Although predator–prey interactions among higher organisms have been studied extensively, only few examples are known for microbes other than protists and viruses. Among the bacteria, the most studied obligate predators are the Bdellovibrio and like organisms (BALOs) that prey on many other bacteria. In the macroscopical world, both predator and prey influence the population size of the other's community, and may have a role in selection. However, selective pressures among prey and predatory bacteria have been rarely investigated. In this study, Bacteriovorax, a predator within the group of BALOs, in environmental waters were fed two prey bacteria, Vibrio vulnificus and Vibrio parahaemolyticus. The two prey species yielded distinct Bacteriovorax populations, evidence that selective pressures shaped the predator community and diversity. The results of laboratory experiments confirmed the differential predation of Bacteriovorax phylotypes on the two bacteria species. Not only did Bacteriovorax Cluster IX exhibit the versatility to be the exclusive efficient predator on Vibrio vulnificus, thereby, behaving as a specialist, but was also able to prey with similar efficiency on Vibrio parahaemolyticus, indicative of a generalist. Therefore, we proposed a designation of versatilist for this predator. This initiative should provide a basis for further efforts to characterize the predatory patterns of bacterial predators. The results of this study have revealed impacts of the prey on Bacteriovorax predation and in structuring the predator community, and advanced understanding of predation behavior in the microbial world. PMID:21326335

  1. [Structure of parasitic arthropod communities in forest small mammals].

    PubMed

    Balashov, Iu S

    2004-01-01

    Species composition and structure of ectoparasite arthropod communities were examined all year round six years in the bank vole Clethrionomys glareolus, Ural wood mouse Apodemus uralensis and the common shrew Sorex araneus in forests of the Ilmen'-Volkhov depression. In total, 4500 host samples have been examined and all ectoparasites have been collected. The species composition of ectoparasite community in small mammal species are as follows: the bank vole--29 insect, tick and mite species, the common shrew--23 species, the Ural wood mouse--16 species. In forest biotopes, many temporary ectoparasitic species occur on several host species living in the same habitats under a forest canopy and contacting each other. A parasitic supracommunity in the ecosystem examined has a pool of temporary ectoparasites, which is available for all the community of small mammals. A role of different rodent and shrew species are hosts of insects and ticks changes depending on a density of potential host populations and numerous other environment factors. PMID:15656091

  2. Impact of oil on bacterial community structure in bioturbated sediments.

    PubMed

    Stauffert, Magalie; Cravo-Laureau, Cristiana; Jézéquel, Ronan; Barantal, Sandra; Cuny, Philippe; Gilbert, Franck; Cagnon, Christine; Militon, Cécile; Amouroux, David; Mahdaoui, Fatima; Bouyssiere, Brice; Stora, Georges; Merlin, François-Xavier; Duran, Robert

    2013-01-01

    Oil spills threaten coastlines where biological processes supply essential ecosystem services. Therefore, it is crucial to understand how oil influences the microbial communities in sediments that play key roles in ecosystem functioning. Ecosystems such as sediments are characterized by intensive bioturbation due to burrowing macrofauna that may modify the microbial metabolisms. It is thus essential to consider the bioturbation when determining the impact of oil on microbial communities. In this study, an experimental laboratory device maintaining pristine collected mudflat sediments in microcosms closer to true environmental conditions--with tidal cycles and natural seawater--was used to simulate an oil spill under bioturbation conditions. Different conditions were applied to the microcosms including an addition of: standardized oil (Blend Arabian Light crude oil, 25.6 mg.g⁻¹ wet sediment), the common burrowing organism Hediste (Nereis) diversicolor and both the oil and H. diversicolor. The addition of H. diversicolor and its associated bioturbation did not affect the removal of petroleum hydrocarbons. After 270 days, 60% of hydrocarbons had been removed in all microcosms irrespective of the H. diversicolor addition. However, 16S-rRNA gene and 16S-cDNA T-RFLP and RT-PCR-amplicon libraries analysis showed an effect of the condition on the bacterial community structure, composition, and dynamics, supported by PerMANOVA analysis. The 16S-cDNA libraries from microcosms where H. diversicolor was added (oiled and un-oiled) showed a marked dominance of sequences related to Gammaproteobacteria. However, in the oiled-library sequences associated to Deltaproteobacteria and Bacteroidetes were also highly represented. The 16S-cDNA libraries from oiled-microcosms (with and without H. diversicolor addition) revealed two distinct microbial communities characterized by different phylotypes associated to known hydrocarbonoclastic bacteria and dominated by Gammaproteobacteria

  3. Differences in the structure and functioning of two communities: Frondose and turf-forming macroalgal dominated habitats.

    PubMed

    M Martins, Gustavo; Hipólito, Cláudia; Parreira, Filipe; C L Prestes, Afonso; Dionísio, Maria A; N Azevedo, José M; Neto, Ana I

    2016-05-01

    In many coastal regions, vegetated habitats (e.g. kelps forests, seagrass beds) play a key role in the structure and functioning of shallow subtidal reef ecosystems, by modifying local environmental conditions and by providing food and habitat for a wide range of organisms. In some regions of the world, however, such idiosyncratic ecosystems are largely absent and are often replaced by less notable ecosystem formers. In the present study, we empirically compared the structure and functioning of two distinct shallow-water habitats present in the Azores: one dominated by smaller frondose brown macroalgae (Dictyotaceae and Halopteris) and one dominated by low-lying turfs. Two replicated areas of each habitat were sampled at two different times of the year, to assess spatial and temporal consistency of results. Habitats dominated by small fronds were significantly (ca. 3 times) more productive (when standardized per algal mass) compared to the turf-dominated habitats, and supported a distinct assemblage (both in terms of composition and abundance) of associated macrofauna. Unlike other well-known and studied vegetated habitats (i.e. kelp forests), however, no effects of habitat were found on the structure of benthonic fish assemblages. Results were spatially and temporally consistent suggesting that, in warmer temperate oceans, habitats dominated by species of smaller frondose brown algae can also play an important role in the structure and functioning of subtidal communities and may, to a certain extent, be considered analogous to other well-known vegetated habitats around the world (i.e. kelp forests, seagrass beds). PMID:27035366

  4. Mass media influence spreading in social networks with community structure

    NASA Astrophysics Data System (ADS)

    Candia, Julián; Mazzitello, Karina I.

    2008-07-01

    We study an extension of Axelrod's model for social influence, in which cultural drift is represented as random perturbations, while mass media are introduced by means of an external field. In this scenario, we investigate how the modular structure of social networks affects the propagation of mass media messages across a society. The community structure of social networks is represented by coupled random networks, in which two random graphs are connected by intercommunity links. Considering inhomogeneous mass media fields, we study the conditions for successful message spreading and find a novel phase diagram in the multidimensional parameter space. These findings show that social modularity effects are of paramount importance for designing successful, cost-effective advertising campaigns.

  5. [Phytoplankton community structure and eutrophication risk assessment of Beijiang River].

    PubMed

    Gou, Ting; Ma, Qian-Li; Xu, Zhen-Cheng; Wang, Li; Li, Jie; Zhao, Xue-Min

    2015-03-01

    To study the distribution of phytoplankton and water quality of Beijiang River, the community structure of phytoplankton was investigated and analyzed in wet and dry seasons. The results showed that a total of 74 species belonging to six phyla, 29 family and 48 genera of phytoplankton were identified, including 58 species of five phyla, 23 family and 41 genera in wet season and 59 species of six phyla, 26 family and 40 genera in dry season. Phytoplankton community structure in Beijiang River was represented by Bacillariophyta, Chlorophyta and Cyanophyta. Bacillariophyta dominanted the phytoplankton, and the dominant species were Aulacoseira granulate, Fragilaria virescens, Surirella biseriata, Nitzschia amphibia, Navicula simplex, Cyclotella meneghiniana, Synedra ulna, Gomphonema angustatum and Cymbella tumida. There was little difference in phytoplankton density between both seasons with the mean values being 3.54 x 10(5) and 4.87 x 10(5) cells L(-1) in dry and wet seasons, respectively. Based on the RDA results, DO, permanganate index, nitrogen and phosphorus were the important environmental factors affecting the distribution of phytoplankton in Beijiang River. The water quality of Beijiang River was classified as oligo-mesotrophic level even if this river was subjected to nitrogen and phosphorus pollution mainly from agricultural non-point source. PMID:25929062

  6. Microbial Community Structure and Enzyme Activities in Semiarid Agricultural Soils

    NASA Astrophysics Data System (ADS)

    Acosta-Martinez, V. A.; Zobeck, T. M.; Gill, T. E.; Kennedy, A. C.

    2002-12-01

    The effect of agricultural management practices on the microbial community structure and enzyme activities of semiarid soils of different textures in the Southern High Plains of Texas were investigated. The soils (sandy clay loam, fine sandy loam and loam) were under continuous cotton (Gossypium hirsutum L.) or in rotations with peanut (Arachis hypogaea L.), sorghum (Sorghum bicolor L.) or wheat (Triticum aestivum L.), and had different water management (irrigated or dryland) and tillage (conservation or conventional). Microbial community structure was investigated using fatty acid methyl ester (FAME) analysis by gas chromatography and enzyme activities, involved in C, N, P and S cycling of soils, were measured (mg product released per kg soil per h). The activities of b-glucosidase, b-glucosaminidase, alkaline phosphatase, and arylsulfatase were significantly (P<0.05) increased in soils under cotton rotated with sorghum or wheat, and due to conservation tillage in comparison to continuous cotton under conventional tillage. Principal component analysis showed FAME profiles of these soils separated distinctly along PC1 (20 %) and PC2 (13 %) due to their differences in soil texture and management. No significant differences were detected in FAME profiles due to management practices for the same soils in this sampling period. Enzyme activities provide early indications of the benefits in microbial populations and activities and soil organic matter under crop rotations and conservation tillage in comparison to the typical practices in semiarid regions of continuous cotton and conventional tillage.

  7. Subsurface chlorophyll maxima in the Skagerrak-processes and plankton community structure

    NASA Astrophysics Data System (ADS)

    Karlson, Bengt; Edler, Lars; Granéli, Wilhelm; Sahlsten, Elisabeth; Kuylenstierna, Mats

    1996-02-01

    Subsurface chlorophyll maxima are common phenomena in both the coastal and open ocean. The main objective of this study was to clarify possible differences in the structure and function of the plankton community in subsurface chlorophyll maxima and at the surface. Sampling was performed at seven stations in the Skagerrak, northeast Atlantic, during five cruises in May and August 1992 and April, May and August 1993. Subsurface chlorophyll fluorescence maxima (FM) occurred on 25 out of 32 sampling occasions. The FMs were usually situated below the pycnocline and associated with the nutricline. The ratio of chlorophyll a to particulate carbon and the light-saturated primary production were higher for plankton at the FM than at the surface, although assimilation numbers (primary production rate: chlorophyll a) were not different from surface plankton. The light protective pigment diadinoxanthin occurred in higher concentrations relative to chlorophyll a in surface plankton than in FM plankton. Respiration was higher in the FM than at the surface. This was not related to abundance of bacteria or bacterial production since no differences between surface and FM values were detected for these parameters. FM plankton was characterized by high nutrient uptake rates, but in this study there were no significant differences compared to surface plankton. 'New' production was on average 25%, but up to about 50% in the western Skagerrak in spring. The average nitrogen uptake rates were dominated by the regenerated nutrients ammonium and urea, accounting for about 50 and 25%, respectively. The <3 μm size fraction contributed significantly to concentrations of total chlorophyll a, particulate carbon, and nitrogen as well as to nitrogen uptake. Its contribution was highest when total values were low. Microscopical investigations and analysis of pigments specific to algal groups showed that diatoms dominated in the FMs in spring and that peridinin-containing dinoflagellates dominated

  8. Algal Flocculation with Synthetic Organic Polyelectrolytes

    PubMed Central

    Tenney, Mark W.; Echelberger, Wayne F.; Schuessler, Ronald G.; Pavoni, Joseph L.

    1969-01-01

    The feasibility of removing algae from water and wastewater by chemical flocculation techniques was investigated. Mixed cultures of algae were obtained from both continuous- and batch-fed laboratory reactors. Representative cationic, anionic, and nonionic synthetic organic polyelectrolytes were used as flocculants. Under the experimental conditions, chemically induced algal flocculation occurred with the addition of cationic polyelectrolyte, but not with anionic or nonionic polymers, although attachment of all polyelectrolyte species to the algal surface is shown. The mechanism of chemically induced algal flocculation is interpreted in terms of bridging phenomena between the discrete algal cells and the linearly extended polymer chains, forming a three-dimensional matrix that is capable of subsiding under quiescent conditions. The degree of flocculation is shown to be a direct function of the extent of polymer coverage of the active sites on the algal surface, although to induce flocculation by this method requires that the algal surface charge must concurrently be reduced to a level at which the extended polymers can bridge the minimal distance of separation imposed by electrostatic repulsion. The influence of pH, algal concentration, and algal growth phase on the requisite cationic flocculant dose is also reported. PMID:5370666

  9. Algal biosensor array on a single electrode.

    PubMed

    Tatsuma, Tetsu; Yoshida, Yutaka; Shitanda, Isao; Notsu, Hideo

    2009-02-01

    An algal array was prepared on a single transparent electrode, and photosynthetic activity of each algal channel and its inhibition by a toxin were monitored with a single-channel potentiostat by successive light irradiation with a LED array. PMID:19173040

  10. TEXAS HARMFUL ALGAL BLOOM COORDINATION MX964014

    EPA Science Inventory

    Harmful algal blooms (HAB) are an expanding problem in coastal Texas. Nearly � of the known harmful algal blooms along the Texas coast have occurred in the past ten years and have led to significant resource and tourism losses. For example, there are at least two types of toxic...

  11. Algal Bloom Detection from HICO

    NASA Astrophysics Data System (ADS)

    Amin, Ruhul; Gould, Richard

    2014-05-01

    Ocean color satellites provide daily, global views of marine bio-optical properties in the upper ocean at various spatial scales. The most productive area of the global ocean is the coastal zone which is heavily impacted by urban and agricultural runoff, transportation, recreation, and oil and gas production. In recent years, harmful algal blooms (HABs) have become one of the serious environmental problems in the coastal areas on a global scale. The global nature of the problem has expanded in its frequency, severity, and extent over the last several decades. Human activities and population increases have contributed to an increase in various toxic and noxious algal species in the coastal regions worldwide. Eutrophication in estuaries and coastal waters is believed to be the major factor causing HABs. In this study, we assess the applicability of the Red Band Difference (RBD) HAB detection algorithm on data from the Hyperspectral Imager for the Coastal Ocean (HICO). Our preliminary results show that due to various uncertainties such as atmospheric correction, calibration and possibly also the relatively low signal-to-noise ratio of HICO for fluorescence detection, it is difficult to extract the fluorescence portion of the reflectance spectrum that RBD uses for bloom detection. We propose an improved bloom detection technique for HICO using red and NIR bands. Our results are validated using other space-borne and ground based measurements.

  12. Network community structure alterations in adult schizophrenia: identification and localization of alterations

    PubMed Central

    Lerman-Sinkoff, Dov B.; Barch, Deanna M.

    2015-01-01

    A growing body of literature suggests functional connectivity alterations in schizophrenia. While findings have been mixed, evidence points towards a complex pattern of hyper-connectivity and hypo-connectivity. This altered connectivity can be represented and analyzed using the mathematical frameworks provided by graph and information theory to represent functional connectivity data as graphs comprised of nodes and edges linking the nodes. One analytic technique in this framework is the determination and analysis of network community structure, which is the grouping of nodes into linked communities or modules. This data-driven technique finds a best-fit structure such that nodes in a given community have greater connectivity with nodes in their community than with nodes in other communities. These community structure representations have been found to recapitulate known neural-systems in healthy individuals, have been used to identify novel functional systems, and have identified and localized community structure alterations in a childhood onset schizophrenia cohort. In the present study, we sought to determine whether community structure alterations were present in an adult onset schizophrenia cohort while stringently controlling for sources of imaging artifacts. Group level average graphs in healthy controls and individuals with schizophrenia exhibited visually similar network community structures and high amounts of normalized mutual information (NMI). However, testing of individual subject community structures identified small but significant alterations in community structure with alterations being driven by changes in node community membership in the somatosensory, auditory, default mode, salience, and subcortical networks. PMID:26793435

  13. Network community structure alterations in adult schizophrenia: identification and localization of alterations.

    PubMed

    Lerman-Sinkoff, Dov B; Barch, Deanna M

    2016-01-01

    A growing body of literature suggests functional connectivity alterations in schizophrenia. While findings have been mixed, evidence points towards a complex pattern of hyper-connectivity and hypo-connectivity. This altered connectivity can be represented and analyzed using the mathematical frameworks provided by graph and information theory to represent functional connectivity data as graphs comprised of nodes and edges linking the nodes. One analytic technique in this framework is the determination and analysis of network community structure, which is the grouping of nodes into linked communities or modules. This data-driven technique finds a best-fit structure such that nodes in a given community have greater connectivity with nodes in their community than with nodes in other communities. These community structure representations have been found to recapitulate known neural-systems in healthy individuals, have been used to identify novel functional systems, and have identified and localized community structure alterations in a childhood onset schizophrenia cohort. In the present study, we sought to determine whether community structure alterations were present in an adult onset schizophrenia cohort while stringently controlling for sources of imaging artifacts. Group level average graphs in healthy controls and individuals with schizophrenia exhibited visually similar network community structures and high amounts of normalized mutual information (NMI). However, testing of individual subject community structures identified small but significant alterations in community structure with alterations being driven by changes in node community membership in the somatosensory, auditory, default mode, salience, and subcortical networks. PMID:26793435

  14. Graph kernels, hierarchical clustering, and network community structure: experiments and comparative analysis

    NASA Astrophysics Data System (ADS)

    Zhang, S.; Ning, X.-M.; Zhang, X.-S.

    2007-05-01

    There has been a quickly growing interest in properties of complex networks, such as the small world property, power-law degree distribution, network transitivity, and community structure, which seem to be common to many real world networks. In this study, we consider the community property which is also found in many real networks. Based on the diffusion kernels of networks, a hierarchical clustering approach is proposed to uncover the community structure of different extent of complex networks. We test the method on some networks with known community structures and find that it can detect significant community structure in these networks. Comparison with related methods shows the effectiveness of the method.

  15. Significance of cyclic Pennsylvanian-Permian coral/algal buildups Snaky Canyon

    SciTech Connect

    Canter, K.L. ); Isaacson, P.E. )

    1991-02-01

    Five cyclic algal, hydrozoan, and coral buildups occur within a thick sequence of Pennsylvanian-Permian (Virgilian through Wolfcampain) carbonates in south-central Idaho. The Juniper Gulch Member of the Snaky Canyon Formation, as described by Skipp and coworkers, is approximately 600 m thick and contains four depositional facies, including: (1) open circulation outer( ) platform, (2) hydrozoan and phylloid algal mound-dominated carbonate buildup, (3) backmound, restricted platform/lagoon, and (4) restricted inner platform facies. Several microlithofacies, including lime mud-rich bafflestone, diversely fossiliferous packstone and grainstone, bryozoan lime floatstone, and phylloid algal and hydrozoan (Palaeoaplysina) lime bindstone are described within the phylloid algal mounds. Successional faunal assemblage stages are recognized within the buildups. Colonial rugose corals comprise a stabilization stage. When the algal communities of the diversification stage reached wave base, because of their rapid upward growth, cross-bedded oolitic grainstone and occasional cross-bedded dolomite shoals developed. Supratidal to high intertidal platform sedimentation is represented by dolomitic Palaeoaplysina bindstone, algal mat bindstone, and vuggy dolomite. Five vertical sequences of buildup development, each terminate by intertidal, supratidal, or erosional events, are seen in the Juniper Gulch Member in the North Howe stratigraphic section of the southern Lost River Range. The carbonate platform was constructed within a depositional basin that includes an eroded highland to the west, and a mixed siliciclastic-carbonate inner platform with craton uplifts to the east.

  16. Soil phosphorus depletion and shifts in plant communities change bacterial community structure in a long-term grassland management trial.

    PubMed

    Adair, Karen L; Wratten, Steve; Lear, Gavin

    2013-06-01

    Agricultural systems rely on healthy soils and their sustainability requires understanding the long-term impacts of agricultural practices on soils, including microbial communities. We examined the impact of 17 years of land management on soil bacterial communities in a New Zealand randomized-block pasture trial. Significant variation in bacterial community structure related to mowing and plant biomass removal, while nitrogen fertilizer had no effect. Changes in soil chemistry and legume abundance described 52% of the observed variation in the bacterial community structure. Legumes (Trifolium species) were absent in unmanaged plots but increased in abundance with management intensity; 11% of the variation in soil bacterial community structure was attributed to this shift in the plant community. Olsen P explained 10% of the observed heterogeneity, which is likely due to persistent biomass removal resulting in P limitation; Olsen P was significantly lower in plots with biomass removed (14 mg kg(-1) ± 1.3SE) compared with plots that were not mown, or where biomass was left after mowing (32 mg kg(-1) ± 1.6SE). Our results suggest that removal of plant biomass and associated phosphorus, as well as shifts in the plant community, have greater long-term impacts on soil bacterial community structure than application of nitrogen fertilizers. PMID:23754721

  17. Constraints to commercialization of algal fuels.

    PubMed

    Chisti, Yusuf

    2013-09-10

    Production of algal crude oil has been achieved in various pilot scale facilities, but whether algal fuels can be produced in sufficient quantity to meaningfully displace petroleum fuels, has been largely overlooked. Limitations to commercialization of algal fuels need to be understood and addressed for any future commercialization. This review identifies the major constraints to commercialization of transport fuels from microalgae. Algae derived fuels are expensive compared to petroleum derived fuels, but this could change. Unfortunately, improved economics of production are not sufficient for an environmentally sustainable production, or its large scale feasibility. A low-cost point supply of concentrated carbon dioxide colocated with the other essential resources is necessary for producing algal fuels. An insufficiency of concentrated carbon dioxide is actually a major impediment to any substantial production of algal fuels. Sustainability of production requires the development of an ability to almost fully recycle the phosphorous and nitrogen nutrients that are necessary for algae culture. Development of a nitrogen biofixation ability to support production of algal fuels ought to be an important long term objective. At sufficiently large scale, a limited supply of freshwater will pose a significant limitation to production even if marine algae are used. Processes for recovering energy from the algal biomass left after the extraction of oil, are required for achieving a net positive energy balance in the algal fuel oil. The near term outlook for widespread use of algal fuels appears bleak, but fuels for niche applications such as in aviation may be likely in the medium term. Genetic and metabolic engineering of microalgae to boost production of fuel oil and ease its recovery, are essential for commercialization of algal fuels. Algae will need to be genetically modified for improved photosynthetic efficiency in the long term. PMID:23886651

  18. Geomorphology and community structure of Middle Reef, central Great Barrier Reef, Australia: an inner-shelf turbid zone reef subject to episodic mortality events

    NASA Astrophysics Data System (ADS)

    Browne, N. K.; Smithers, S. G.; Perry, C. T.

    2010-09-01

    Middle Reef is an inshore turbid zone reef located 4 km offshore from Townsville, Queensland, Australia. The reef consists of four current-aligned, interconnected reef patches that have reached sea level and formed reef flats. It is regularly exposed to high turbidity (up to 50 mg l-1) generated by wave-driven sediment resuspension or by episodic flood plumes. Middle Reef has a high mean hard coral cover (>39%), relatively low mean macro-algal cover (<15%) and a coral community comprising at least 81 hard coral species. Cluster analysis differentiated six benthic communities which were mapped onto the geomorphological structure of the reef to reveal a spatially patchy community mosaic that reflects hydrodynamic and sediment redistribution processes. Coral cover data collected annually from windward slope transects since 1993 show that coral cover has increased over the last ~15 years despite a history of episodic mortality events. Although episodic mortality may be interpreted as an indication of marginality, over decadal timescales, Middle Reef has recovered rapidly following mortality events and is clearly a resilient coral reef.

  19. Measuring Cellular-scale Nutrient Distribution in Algal Biofilms with Synchrotron Confocal Infrared Microspectroscopy

    SciTech Connect

    J Murdock; W Dodds; J Reffner; D Wetzel

    2011-12-31

    -dwelling) algae, for example, grow in a three-dimensional matrix (biofilm) composed of different cell sizes, shapes, and configurations. The optical and ecological challenge of studying algae is apparent from Figure 1, which shows a photomicrograph of algal chlorophyll fluorescence on a rock. Several issues make it difficult to obtain single species measurements with standard techniques: cell sizes can vary over an order of magnitude; species can occur as single cells, long filaments, or globular colonies; a number of different species can be found within a few square millimeters; and fluorescence can vary across cells (that is, the physiological state varies across cells). Synchrotron IMS is a tool that can be used to begin to overcome these spatially related challenges by giving a species- and location-specific measurement of an individual alga's relative chemical composition and distribution. This technique enables algal ecologists to focus on new, ecologically relevant questions such as what level (that is, cell, colony, and population) best defines a species' response to environmental change. For instance, many species occur as single cells and thus can be measured as individual organisms. However, the variety of growth forms and sizes can make it difficult to define the best unit to measure multicellular groups in terms of its functional role such as primary productivity (that is, carbon incorporation) and nutrient cycling. Understanding how individual algal species within a diverse community respond to environmental changes can help predict how changes in assemblage structure will impact overall assemblage function.

  20. Internal Transcribed Spacer 2 (nu ITS2 rRNA) Sequence-Structure Phylogenetics: Towards an Automated Reconstruction of the Green Algal Tree of Life

    PubMed Central

    Buchheim, Mark A.; Keller, Alexander; Koetschan, Christian; Förster, Frank; Merget, Benjamin; Wolf, Matthias

    2011-01-01

    Background Chloroplast-encoded genes (matK and rbcL) have been formally proposed for use in DNA barcoding efforts targeting embryophytes. Extending such a protocol to chlorophytan green algae, though, is fraught with problems including non homology (matK) and heterogeneity that prevents the creation of a universal PCR toolkit (rbcL). Some have advocated the use of the nuclear-encoded, internal transcribed spacer two (ITS2) as an alternative to the traditional chloroplast markers. However, the ITS2 is broadly perceived to be insufficiently conserved or to be confounded by introgression or biparental inheritance patterns, precluding its broad use in phylogenetic reconstruction or as a DNA barcode. A growing body of evidence has shown that simultaneous analysis of nucleotide data with secondary structure information can overcome at least some of the limitations of ITS2. The goal of this investigation was to assess the feasibility of an automated, sequence-structure approach for analysis of IT2 data from a large sampling of phylum Chlorophyta. Methodology/Principal Findings Sequences and secondary structures from 591 chlorophycean, 741 trebouxiophycean and 938 ulvophycean algae, all obtained from the ITS2 Database, were aligned using a sequence structure-specific scoring matrix. Phylogenetic relationships were reconstructed by Profile Neighbor-Joining coupled with a sequence structure-specific, general time reversible substitution model. Results from analyses of the ITS2 data were robust at multiple nodes and showed considerable congruence with results from published phylogenetic analyses. Conclusions/Significance Our observations on the power of automated, sequence-structure analyses of ITS2 to reconstruct phylum-level phylogenies of the green algae validate this approach to assessing diversity for large sets of chlorophytan taxa. Moreover, our results indicate that objections to the use of ITS2 for DNA barcoding should be weighed against the utility of an automated

  1. Interlinking backscatter, grain size and benthic community structure

    NASA Astrophysics Data System (ADS)

    McGonigle, Chris; Collier, Jenny S.

    2014-06-01

    The relationship between acoustic backscatter, sediment grain size and benthic community structure is examined using three different quantitative methods, covering image- and angular response-based approaches. Multibeam time-series backscatter (300 kHz) data acquired in 2008 off the coast of East Anglia (UK) are compared with grain size properties, macrofaunal abundance and biomass from 130 Hamon and 16 Clamshell grab samples. Three predictive methods are used: 1) image-based (mean backscatter intensity); 2) angular response-based (predicted mean grain size), and 3) image-based (1st principal component and classification) from Quester Tangent Corporation Multiview software. Relationships between grain size and backscatter are explored using linear regression. Differences in grain size and benthic community structure between acoustically defined groups are examined using ANOVA and PERMANOVA+. Results for the Hamon grab stations indicate significant correlations between measured mean grain size and mean backscatter intensity, angular response predicted mean grain size, and 1st principal component of QTC analysis (all p < 0.001). Results for the Clamshell grab for two of the methods have stronger positive correlations; mean backscatter intensity (r2 = 0.619; p < 0.001) and angular response predicted mean grain size (r2 = 0.692; p < 0.001). ANOVA reveals significant differences in mean grain size (Hamon) within acoustic groups for all methods: mean backscatter (p < 0.001), angular response predicted grain size (p < 0.001), and QTC class (p = 0.009). Mean grain size (Clamshell) shows a significant difference between groups for mean backscatter (p = 0.001); other methods were not significant. PERMANOVA for the Hamon abundance shows benthic community structure was significantly different between acoustic groups for all methods (p ≤ 0.001). Overall these results show considerable promise in that more than 60% of the variance in the mean grain size of the Clamshell grab

  2. Predator foraging altitudes reveal the structure of aerial insect communities.

    PubMed

    Helms, Jackson A; Godfrey, Aaron P; Ames, Tayna; Bridge, Eli S

    2016-01-01

    The atmosphere is populated by a diverse array of dispersing insects and their predators. We studied aerial insect communities by tracking the foraging altitudes of an avian insectivore, the Purple Martin (Progne subis). By attaching altitude loggers to nesting Purple Martins and collecting prey delivered to their nestlings, we determined the flight altitudes of ants and other insects. We then tested hypotheses relating ant body size and reproductive ecology to flight altitude. Purple Martins flew up to 1,889 meters above ground, and nestling provisioning trips ranged up to 922 meters. Insect communities were structured by body size such that species of all sizes flew near the ground but only light insects flew to the highest altitudes. Ant maximum flight altitudes decreased by 60% from the lightest to the heaviest species. Winged sexuals of social insects (ants, honey bees, and termites) dominated the Purple Martin diet, making up 88% of prey individuals and 45% of prey biomass. By transferring energy from terrestrial to aerial food webs, mating swarms of social insects play a substantial role in aerial ecosystems. Although we focus on Purple Martins and ants, our combined logger and diet method could be applied to a range of aerial organisms. PMID:27352817

  3. [Arthropod community structures in transgenic Bt cotton fields].

    PubMed

    Wei, G; Cui, L; Zhang, X; Liu, S; Lü, N; Zhang, Q

    2001-08-01

    Arthropod community structures were investigated in transgenic Bt cultivars, Bollgard(B) and Chinese cotton 30 (CC30), and common cultivars, control (C) and no control (NC) cotton field in North China in 1998. The results showed that compared with common cultivars, the species richness and the number of total individual of arthropod community in transgenic Bt cultivars field were reduced 2.4-16.3% and 71.0-78.3% respectively, in which dominant species in phytophagous subcommunity varied. The number of individual of predatory and parastic subcommunity were all increased. The similarity coefficient between CC30 and NC was 0.8243, B and NC 0.7320, B and C 0.3380, C and NC 0.3128, CC30 and C 0.2665. The order of diversity and evenness value of these were CC30 (2.3712 and 0.6428), NC (2.3654 and 0.6251), B (2.1364 and 0.5791), and C (1.0877 and 0.2949), their dominant value was 0.8726 (C), 0.3528(B), 0.1178(NC) and 0.1048 (CC30) respectively. It was concluded that different integrated pest management (IPM) strategy should be implemented in transgenic Bt cotton instead of common variety cotton field. PMID:11758387

  4. Aquifer community structure in dependence of lithostratigraphy in groundwater reservoirs.

    PubMed

    Beyer, Andrea; Rzanny, Michael; Weist, Aileen; Möller, Silke; Burow, Katja; Gutmann, Falko; Neumann, Stefan; Lindner, Julia; Müsse, Steffen; Brangsch, Hanka; Stoiber-Lipp, Jennifer; Lonschinski, Martin; Merten, Dirk; Büchel, Georg; Kothe, Erika

    2015-12-01

    Groundwater microbiology with respect to different host rocks offers new possibilities to describe and map the habitat harboring approximately half of Earths' biomass. The Thuringian Basin (Germany) contains formations of the Permian (Zechstein) and Triassic (Muschelkalk and Buntsandstein) with outcrops and deeper regions at the border and central part. Hydro(geo)chemistry and bacterial community structure of 11 natural springs and 20 groundwater wells were analyzed to define typical patterns for each formation. Widespread were Gammaproteobacteria, while Bacilli were present in all wells. Halotolerant and halophilic taxa were present in Zechstein. The occurrence of specific taxa allowed a clear separation of communities from all three lithostratigraphic groups. These specific taxa could be used to follow fluid movement, e.g., from the underlying Zechstein or from nearby saline reservoirs into Buntsandstein aquifers. Thus, we developed a new tool to identify the lithostratigraphic origin of sources in mixed waters. This was verified with entry of surface water, as species not present in the underground Zechstein environments were isolated from the water samples. Thus, our tool shows a higher resolution as compared to hydrochemistry, which is prone to undergo fast dilution if water mixes with other aquifers. Furthermore, the bacteria well adapted to their respective environment showed geographic clustering allowing to differentiate regional aquifers. PMID:26002361

  5. Predator foraging altitudes reveal the structure of aerial insect communities

    PubMed Central

    Helms, Jackson A.; Godfrey, Aaron P.; Ames, Tayna; Bridge, Eli S.

    2016-01-01

    The atmosphere is populated by a diverse array of dispersing insects and their predators. We studied aerial insect communities by tracking the foraging altitudes of an avian insectivore, the Purple Martin (Progne subis). By attaching altitude loggers to nesting Purple Martins and collecting prey delivered to their nestlings, we determined the flight altitudes of ants and other insects. We then tested hypotheses relating ant body size and reproductive ecology to flight altitude. Purple Martins flew up to 1,889 meters above ground, and nestling provisioning trips ranged up to 922 meters. Insect communities were structured by body size such that species of all sizes flew near the ground but only light insects flew to the highest altitudes. Ant maximum flight altitudes decreased by 60% from the lightest to the heaviest species. Winged sexuals of social insects (ants, honey bees, and termites) dominated the Purple Martin diet, making up 88% of prey individuals and 45% of prey biomass. By transferring energy from terrestrial to aerial food webs, mating swarms of social insects play a substantial role in aerial ecosystems. Although we focus on Purple Martins and ants, our combined logger and diet method could be applied to a range of aerial organisms. PMID:27352817

  6. A novel dynamics combination model reveals the hidden information of community structure

    NASA Astrophysics Data System (ADS)

    Li, Hui-Jia; Li, Huiying; Jia, Chuanliang

    2015-09-01

    The analysis of the dynamic details of community structure is an important question for scientists from many fields. In this paper, we propose a novel Markov-Potts framework to uncover the optimal community structures and their stabilities across multiple timescales. Specifically, we model the Potts dynamics to detect community structure by a Markov process, which has a clear mathematical explanation. Then the local uniform behavior of spin values revealed by our model is shown that can naturally reveal the stability of hierarchical community structure across multiple timescales. To prove the validity, phase transition of stochastic dynamic system is used to indicate that the stability of community structure we proposed is able to describe the significance of community structure based on eigengap theory. Finally, we test our framework on some example networks and find it does not have resolute limitation problem at all. Results have shown the model we proposed is able to uncover hierarchical structure in different scales effectively and efficiently.

  7. Characterization and Comparison of the Structural Features, Immune-Modulatory and Anti-Avian Influenza Virus Activities Conferred by Three Algal Sulfated Polysaccharides

    PubMed Central

    Song, Lin; Chen, Xiaolin; Liu, Xiaodong; Zhang, Fubo; Hu, Linfeng; Yue, Yang; Li, Kecheng; Li, Pengcheng

    2015-01-01

    Three marine macroalgae, i.e., Grateloupia filicina, Ulva pertusa and Sargassum qingdaoense, were selected as the deputies of Rhodophyta, Chlorophyta and Ochrophyta for comparative analysis of the molecular structures and biological activities of sulfated polysaccharides (SP). The ratio of water-soluble polysaccharides, the monosaccharide composition and the sulfated contents of three extracted SPs were determined, and their structures were characterized by Fourier transformation infrared spectroscopy. In addition, biological activity analysis showed that all three SPs had immune-modulatory activity both in vitro and in vivo, and SPs from S. qingdaoense had the best effect. Further bioassays showed that three SPs could not only enhance the immunity level stimulated by inactivated avian influenza virus (AIV) in vivo but also significantly inhibited the activity of activated AIV (H9N2 subtype) in vitro. G. filicina SP exhibited the strongest anti-AIV activity. These results revealed the variations in structural features and bioactivities among three SPs and indicated the potential adjuvants for immune-enhancement and anti-AIV. PMID:26729137

  8. Characterization and Comparison of the Structural Features, Immune-Modulatory and Anti-Avian Influenza Virus Activities Conferred by Three Algal Sulfated Polysaccharides.

    PubMed

    Song, Lin; Chen, Xiaolin; Liu, Xiaodong; Zhang, Fubo; Hu, Linfeng; Yue, Yang; Li, Kecheng; Li, Pengcheng

    2016-01-01

    Three marine macroalgae, i.e., Grateloupia filicina, Ulva pertusa and Sargassum qingdaoense, were selected as the deputies of Rhodophyta, Chlorophyta and Ochrophyta for comparative analysis of the molecular structures and biological activities of sulfated polysaccharides (SP). The ratio of water-soluble polysaccharides, the monosaccharide composition and the sulfated contents of three extracted SPs were determined, and their structures were characterized by Fourier transformation infrared spectroscopy. In addition, biological activity analysis showed that all three SPs had immune-modulatory activity both in vitro and in vivo, and SPs from S. qingdaoense had the best effect. Further bioassays showed that three SPs could not only enhance the immunity level stimulated by inactivated avian influenza virus (AIV) in vivo but also significantly inhibited the activity of activated AIV (H9N2 subtype) in vitro. G. filicina SP exhibited the strongest anti-AIV activity. These results revealed the variations in structural features and bioactivities among three SPs and indicated the potential adjuvants for immune-enhancement and anti-AIV. PMID:26729137

  9. Are gay communities dying or just in transition? Results from an international consultation examining possible structural change in gay communities.

    PubMed

    Simon Rosser, B R; West, William; Weinmeyer, Richard

    2008-05-01

    This study sought to identify how urban gay communities are undergoing structural change, reasons for that change, and implications for HIV prevention planning. Key informants (N=29) at the AIDS Impact Conference from 17 cities in 14 countries completed surveys and participated in a facilitated structured dialog about if gay communities are changing, and if so, how they are changing. In all cities, the virtual gay community was identified as currently larger than the offline physical community. Most cities identified that while the gay population in their cities appeared stable or growing, the gay community appeared in decline. Measures included greater integration of heterosexuals into historically gay-identified neighborhoods and movement of gay persons into suburbs, decreased number of gay bars/clubs, less attendance at gay events, less volunteerism in gay or HIV/AIDS organizations, and the overall declining visibility of gay communities. Participants attributed structural change to multiple factors including gay neighborhood gentrification, achievement of civil rights, less discrimination, a vibrant virtual community, and changes in drug use. Consistent with social assimilation, gay infrastructure, visibility, and community identification appears to be decreasing across cities. HIV prevention planning, interventions, treatment services, and policies need to be re-conceptualized for MSM in the future. Four recommendations for future HIV prevention and research are detailed. PMID:18484330

  10. Aphid–parasitoid community structure on genetically modified wheat

    PubMed Central

    von Burg, Simone; van Veen, Frank J. F.; Álvarez-Alfageme, Fernando; Romeis, Jörg

    2011-01-01

    Since the introduction of genetically modified (GM) plants, one of the main concerns has been their potential effect on non-target insects. Many studies have looked at GM plant effects on single non-target herbivore species or on simple herbivore–natural enemy food chains. Agro-ecosystems, however, are characterized by numerous insect species which are involved in complex interactions, forming food webs. In this study, we looked at transgenic disease-resistant wheat (Triticum aestivum) and its effect on aphid–parasitoid food webs. We hypothesized that the GM of the wheat lines directly or indirectly affect aphids and that these effects cascade up to change the structure of the associated food webs. Over 2 years, we studied different experimental wheat lines under semi-field conditions. We constructed quantitative food webs to compare their properties on GM lines with the properties on corresponding non-transgenic controls. We found significant effects of the different wheat lines on insect community structure up to the fourth trophic level. However, the observed effects were inconsistent between study years and the variation between wheat varieties was as big as between GM plants and their controls. This suggests that the impact of our powdery mildew-resistant GM wheat plants on food web structure may be negligible and potential ecological effects on non-target insects limited. PMID:21247941

  11. Iterated tabu search for identifying community structure in complex networks

    NASA Astrophysics Data System (ADS)

    Lü, Zhipeng; Huang, Wenqi

    2009-08-01

    This paper presents an iterated tabu search (denoted by ITS) algorithm for optimizing the modularity of community structure in complex networks. The proposed algorithm follows a general framework composed of two phases: basic optimization and postrefinement. When the basic optimization cannot improve the modularity any more, a postrefinement procedure is employed to further optimize the objective function with a global view. For both these two phases, iterated tabu search algorithm is employed to optimize the objective function. Computational results show the high effectiveness of the proposed ITS algorithm compared with six state-of-the-art algorithms in the literature. In particular, our ITS algorithm improves the previous best known modularity for several small and medium size networks.

  12. Iterated tabu search for identifying community structure in complex networks.

    PubMed

    Lü, Zhipeng; Huang, Wenqi

    2009-08-01

    This paper presents an iterated tabu search (denoted by ITS) algorithm for optimizing the modularity of community structure in complex networks. The proposed algorithm follows a general framework composed of two phases: basic optimization and postrefinement. When the basic optimization cannot improve the modularity any more, a postrefinement procedure is employed to further optimize the objective function with a global view. For both these two phases, iterated tabu search algorithm is employed to optimize the objective function. Computational results show the high effectiveness of the proposed ITS algorithm compared with six state-of-the-art algorithms in the literature. In particular, our ITS algorithm improves the previous best known modularity for several small and medium size networks. PMID:19792223

  13. Algal Accessory Pigment Detection Using AVIRIS Image-Derived Spectral Radiance Data

    NASA Technical Reports Server (NTRS)

    Richardson, Laurie L.; Ambrosia, Vincent G.

    1996-01-01

    Visual and derivative analyses of AVIRIS spectral data can be used to detect algal accessory pigments in aquatic communities. This capability extends the use of remote sensing for the study of aquatic ecosystems by allowing detection of taxonomically significant pigment signatures which yield information about the type of algae present. Such information allows remote sensing-based assessment of aquatic ecosystem health, as in the detection of nuisance blooms of cyanobacteria or toxic blooms of dinoflagellates. Remote sensing of aquatic systems has traditionally focused on quantification of chlorophyll a, a photoreactive (and light-harvesting) pigment which is common to all algae as well as cyanobacteria (bluegreen algae). Due to the ubiquitousness of this pigment within algae, chl a is routinely measured to estimate algal biomass both during ground-truthing and using various airborne or satellite based sensors, including AVIRIS. Within the remote sensing and aquatic sciences communities, ongoing research has been performed to detect algal accessory pigments for assessment of algal population composition. This research is based on the fact that many algal accessory pigments are taxonomically significant, and all are spectrally unique. Aquatic scientists have been refining pigment analysis techniques, primarily high performance liquid chromatography, or HPLC, to detect specific pigments as a time-saving alternative to individual algal cell identifications and counts. Remote sensing scientists are investigating the use of pigment signatures to construct pigment libraries analogous to mineral spectral libraries used in geological remote sensing applications. The accessory pigment approach has been used successfully in remote sensing using data from the Thematic Mapper, low-altitude, multiple channel scanners, field spectroradiometers and the AVIRIS hyperspectral scanner. Due to spectral and spatial resolution capabilities, AVIRIS is the sensor of choice for such

  14. Unraveling the Molecular Mechanisms Underlying the Nasopharyngeal Bacterial Community Structure.

    PubMed

    de Steenhuijsen Piters, Wouter A A; Bogaert, Debby

    2016-01-01

    The upper respiratory tract is colonized by a diverse array of commensal bacteria that harbor potential pathogens, such as Streptococcus pneumoniae. As long as the local microbial ecosystem-also called "microbiome"-is in balance, these potentially pathogenic bacterial residents cause no harm to the host. However, similar to macrobiological ecosystems, when the bacterial community structure gets perturbed, potential pathogens can overtake the niche and cause mild to severe infections. Recent studies using next-generation sequencing show that S. pneumoniae, as well as other potential pathogens, might be kept at bay by certain commensal bacteria, including Corynebacterium and Dolosigranulum spp. Bomar and colleagues are the first to explore a specific biological mechanism contributing to the antagonistic interaction between Corynebacterium accolens and S. pneumoniae in vitro [L. Bomar, S. D. Brugger, B. H. Yost, S. S. Davies, K. P. Lemon, mBio 7(1):e01725-15, 2016, doi:10.1128/mBio.01725-15]. The authors comprehensively show that C. accolens is capable of hydrolyzing host triacylglycerols into free fatty acids, which display antipneumococcal properties, suggesting that these bacteria might contribute to the containment of pneumococcus. This work exemplifies how molecular epidemiological findings can lay the foundation for mechanistic studies to elucidate the host-microbe and microbial interspecies interactions underlying the bacterial community structure. Next, translation of these results to an in vivo setting seems necessary to unveil the magnitude and importance of the observed effect in its natural, polymicrobial setting. PMID:26838716

  15. Unraveling the Molecular Mechanisms Underlying the Nasopharyngeal Bacterial Community Structure

    PubMed Central

    de Steenhuijsen Piters, Wouter A. A.

    2016-01-01

    ABSTRACT The upper respiratory tract is colonized by a diverse array of commensal bacteria that harbor potential pathogens, such as Streptococcus pneumoniae. As long as the local microbial ecosystem—also called “microbiome”—is in balance, these potentially pathogenic bacterial residents cause no harm to the host. However, similar to macrobiological ecosystems, when the bacterial community structure gets perturbed, potential pathogens can overtake the niche and cause mild to severe infections. Recent studies using next-generation sequencing show that S. pneumoniae, as well as other potential pathogens, might be kept at bay by certain commensal bacteria, including Corynebacterium and Dolosigranulum spp. Bomar and colleagues are the first to explore a specific biological mechanism contributing to the antagonistic interaction between Corynebacterium accolens and S. pneumoniae in vitro [L. Bomar, S. D. Brugger, B. H. Yost, S. S. Davies, K. P. Lemon, mBio 7(1):e01725-15, 2016, doi:10.1128/mBio.01725-15]. The authors comprehensively show that C. accolens is capable of hydrolyzing host triacylglycerols into free fatty acids, which display antipneumococcal properties, suggesting that these bacteria might contribute to the containment of pneumococcus. This work exemplifies how molecular epidemiological findings can lay the foundation for mechanistic studies to elucidate the host-microbe and microbial interspecies interactions underlying the bacterial community structure. Next, translation of these results to an in vivo setting seems necessary to unveil the magnitude and importance of the observed effect in its natural, polymicrobial setting. PMID:26838716

  16. Outer-membrane cytochrome-c, OmcF from Geobacter sulfurreducens: high structural similarity to an algal cytochrome c6.

    SciTech Connect

    Pokkuluri, P. R.; Londer, Y. Y.; Wood, S. J.; Duke, N. E. C.; Morgado, L.; Salgueiro, C. A.; Schiffer, M.; Biosciences Division; Univ. Nova de Lisboa

    2009-01-01

    Putative outer membrane c-type cytochromes have been implicated in metal ion reducing properties of Geobacter sulfurreducens. OmcF (GSU2432), OmcB (GSU2731), and OmcC (GSU2737) are three such proteins that have predicted lipid anchors. OmcF is a monoheme cytochrome, whereas OmcB and OmcC are multiheme cytochromes. Deletion of OmcF was reported to affect the expression of OmcB and OmcC in G. sulfurreducens. The OmcF deficient strain was impaired in its ability to both reduce and grow on Fe(III) citrate probably because the expression of OmcB, which is crucial for iron reduction, is low in this strain. U(VI) reduction activity of this bacterium is also lower on deletion of OmcB or OmcF. The U(VI) reduction activity is affected more by the deletion of OmcF than by the deletion of OmcB. The soluble part of OmcF (residues 20-104, referred to as OmcF{sub S} hereafter) has sequence similarity to soluble cytochromes c{sub 6} of photosynthetic algae and cyanobacteria. The cytochrome c{sub 6} proteins in algae and cyanobacteria are electron transport proteins that mediate the transfer of electrons from cytochrome b{sub 6}f to photosystem I and have high reduction potentials of about +350 mV and low pI. The structures of seven cytochromes c{sub 6} have been previously determined. Further, a c{sub 6}-like cytochrome (PetJ2) of unknown function was recently identified in Synechoccus sp. PCC 7002 with a reduction potential of +148 mV and high pI. Here, we report the structure of OmcF{sub S} and its remarkable structural similarity to that of cytochrome c{sub 6} from the green alga, Monoraphidium braunii. To our knowledge, OmcF{sub S} is the first example of a cytochrome c{sub 6}-like structure from a nonphotosynthetic organism.

  17. ORGANIC VS CONVENTIONAL: SOIL NEMATODE COMMUNITY STRUCTURE AND FUNCTION.

    PubMed

    Kapp, C; Storey, S G; Malan, A P

    2014-01-01

    Global increases in human population are creating an ever-greater need for food production. Poor soil management practices have degraded soil to such an extent that rapidly improved management practices is the only way to ensure future food demands. In South Africa, deciduous fruit producers are realising the need for soil health, and for an increased understanding of the benefits of soil ecology, to ensure sustainable fruit production. This depends heavily on improved orchard management. Conventional farming relies on the addition of artificial fertilizers, and the application of chemicals, to prevent or minimise, the effects of the soil stages of pest insects, and of plant-parasitic nematodes. Currently, there is resistance toward conventional farming practices, which, it is believed, diminishes biodiversity within the soil. The study aimed to establish the soil nematode community structure and function in organically, and conventionally, managed deciduous fruit orchards. This was done by determining the abundance, the diversity, and the functionality of the naturally occurring free-living, and plant-parasitic, nematodes in deciduous fruit orchards in the Western Cape province of South Africa. The objective of the study was to form the basis for the use of nematodes as future indicators of soil health in deciduous fruit orchards. Orchards from neighbouring organic, and conventional, apricot farms, and from an organic apple orchard, were studied. All the nematodes were quantified, and identified, to family level. The five nematode-classified trophic groups were found at each site, while 14 families were identified in each orchard, respectively. Herbivores were dominant in all the orchards surveyed. Organic apples had the fewest herbivores and fungivores, with the highest number of carnivores. When comparing organic with conventional apricot orchards, higher numbers of plant-parasitic nematodes were found in the organic apricot orchards. The Maturity Index (MI

  18. Pregnancy and birth in an indigenous Huichol community: from structural violence to structural policy responses.

    PubMed

    Gamlin, Jennie B; Hawkes, Sarah J

    2015-01-01

    Mexico's indigenous regions are characterised by socio-economic marginalisation and poor health outcomes and the Maternal Mortality Rate in indigenous communities continues to be around six times higher than the national rate. Using as a case study the Huichol community of North-Western Mexico we will discuss how institutional health and welfare programmes which aim to address accepted risk factors for maternal health are undermined by a series of structural barriers which put indigenous women especially in harm's way. Semi-structured interviews and observational data were gathered between 2009 and 2011 in highland communities and on coastal tobacco plantations to where a large number of this ethnic group migrate. Many Huichol women birth alone, and to facilitate this process they maintain a low nutritional intake to reduce their infant's growth and seek spiritual guidance during pregnancy from a shaman. These practices are reinforced by feelings of shame and humiliation encountered when using institutional health provision. These are some of the structural barriers to care that need to be addressed. Effective interventions could include addressing the training of health professionals, focusing on educational inequalities and the structural determinants of poverty whilst designing locally specific programmes that encourage acceptance of available health care. PMID:25175749

  19. Community structure, population structure and topographical specialisation of Gyrodactylus (monogenea) ectoparasites living on sympatric stickleback species.

    PubMed

    Raeymaekers, Joost A M; Huyse, Tine; Maelfait, Hannelore; Hellemans, Bart; Volckaert, Filip A M

    2008-09-01

    In order to disentangle the contribution of host and parasite biology to host specificity, we compared the structure and population dynamics of the Gyrodactylus (von Nordmann, 1832) flatworm community living on sympatric three-spined Gasterosteus aculeatus L. and nine-spined Pungitius pungitius (L.) stickleback. Between April 2002 and March 2003, a small lowland creek was sampled monthly. Species identity of about 75% of the worms per host was determined with a genetic nuclear marker (ITS1). Each stickleback species hosted a characteristic gill- and fin-parasitic Gyrodactylus: G. arcuatus Bychowsky, 1933 and G. gasterostei Gläser, 1974 respectively infecting the three-spined stickleback, with G. rarus Wegener, 1910 and G. pungitii Malmberg, 1964 infecting the nine-spined stickleback. Host size and seasonal dynamics were strong determinants of parasite abundance. A strong interaction between host and parasite species determined infection levels and affected three levels of parasite organisation: community structure, population structure and topographical specialisation. Community and population structure were shaped by asymmetric cross-infections, resulting in a net transmission of the Gyro-dactylus species typical of the nine-spined stickleback towards the three-spined stickleback. Host density was not a major determinant of parasite exchange. Aggregation and topographical specialisation of the Gyrodactylus species of the three-spined stickleback were more pronounced than that of the nine-spined stickleback. PMID:19202677

  20. Nutrient ratios and the complex structure of phytoplankton communities in a highly turbid estuary of Southeast Asia.

    PubMed

    Chu, Thuoc Van; Torréton, Jean-Pascal; Mari, Xavier; Nguyen, Huyen Minh Thi; Pham, Kha Thi; Pham, Thu The; Bouvier, Thierry; Bettarel, Yvan; Pringault, Olivier; Bouvier, Corinne; Rochelle-Newall, Emma

    2014-12-01

    Phytoplankton diversity and abundance in estuarine systems are controlled by many factors. Salinity, turbidity, and inorganic nutrient concentrations and their respective ratios have all been proposed as principal factors that structure phytoplankton diversity and influence the emergence of potentially toxic species. Although much work has been conducted on temperate estuaries, less is known about how phytoplankton diversity is controlled in tropical, monsoonal systems that are subject to large, seasonal shifts in hydrology and to rapidly changing land use. Here, we present the results of an investigation into the factors controlling phytoplankton species composition and distribution in a tropical, monsoonal estuary (Bach Dang estuary, North Vietnam). A total of 245 taxa, 89 genera from six algal divisions were observed. Bacillariophyceae were the most diverse group contributing to 51.4 % of the microalgal assemblage, followed by Dinophyceae (29.8 %), Chlorophyceae (10.2 %), Cyanophyceae (3.7 %), Euglenophyceae (3.7 %) and Dictyochophyceae (1.2 %). The phytoplankton community was structured by inorganic nutrient ratios (DSi:DIP and DIN:DIP) as well as by salinity and turbidity. Evidence of a decrease in phytoplankton diversity concomitant with an increase in abundance and dominance of certain species (e.g., Skeletonema costatum) and the appearance of some potentially toxic species over the last two decades was also found. These changes in phytoplankton diversity are probably due to a combination of land use change resulting in changes in nutrient ratios and concentrations and global change as both rainfall and temperature have increased over the last two decades. It is therefore probable in the future that phytoplankton diversity will continue to change, potentially favoring the emergence of toxic species in this system. PMID:25200992

  1. Four Structures for Marketing in the American Public Community College.

    ERIC Educational Resources Information Center

    Bogart, Quentin J.

    Prepared for college officials considering the development of marketing programs, this paper examines the distinctive marketing practices for four geographically separated, public community college districts: Coastline Community College (CCC), California; Metropolitan Community College District (MCCD), Missouri; Triton College (TC), Illinois; and…

  2. Algal lectin binding to core (α1-6) fucosylated N-glycans: structural basis for specificity and production of recombinant protein.

    PubMed

    do Nascimento, Antônia S F; Serna, Sonia; Beloqui, Ana; Arda, Ana; Sampaio, Alexandre H; Walcher, Janika; Ott, Dimitri; Unverzagt, Carlo; Reichardt, Niels-Christian; Jimenez-Barbero, Jesus; Nascimento, Kyria S; Imberty, Anne; Cavada, Benildo S; Varrot, Annabelle

    2015-06-01

    We determined the specificity of BTL, a lectin from the red marine alga Bryothamnion triquetrum, toward fucosylated oligosaccharides. BTL showed a strict specificity for the core α1,6-fucosylation, which is an important marker for cancerogenesis and quality control of therapeutical antibodies. The double fucosylation α1,6 and α1,3 was also recognized, but the binding was totally abolished in the sole presence of the α1,3-fucosylation. A more detailed analysis of the specificity of BTL showed a preference for bi- and tri-antennary nonbisected N-glycans. Sialylation or fucosylation at the nonreducing end of N-glycans did not affect the recognition by the lectin. BTL displayed a strong affinity for a core α1,6-fucosylated octasaccharide with a Kd of 12 μM by titration microcalorimetry. The structural characterization of the interaction between BTL and the octasaccharide was obtained by STD-NMR. It demonstrated an extended epitope for recognition that includes the fucose residue, the distal GlcNAc and one mannose residue. Recombinant rBTL was obtained in Escherichia coli and characterized. Its binding properties for carbohydrates were studied using hemagglutination tests and glycan array analysis. rBTL was able to agglutinate rabbit erythrocytes with strong hemagglutination activity only after treatment with papain and trypsin, indicating that its ligands were not directly accessible at the cell surface. The hemagglutinating properties of rBTL confirm the correct folding and functional state of the protein. The results show BTL as a potent candidate for cancer diagnosis and as a reagent for the preparation and quality control of antibodies lacking core α1,6-fucosylated N-glycans. PMID:25573275

  3. Microzooplankton herbivory and community structure in the Amundsen Sea, Antarctica

    NASA Astrophysics Data System (ADS)

    Yang, Eun Jin; Jiang, Yong; Lee, SangHoon

    2016-01-01

    We examined microzooplankton abundance, community structure, and grazing impact on phytoplankton in the Amundsen Sea, Western Antarctica, during the early austral summer from December 2010 to January 2011. Our study area was divided into three regions based on topography, hydrographic properties, and trophic conditions: (1) the Oceanic Zone (OZ), with free sea ice and low phytoplankton biomass dominated by diatoms; (2) the Sea Ice Zone (SIZ), covered by heavy sea ice with colder water, lower salinity, and dominated by diatoms; and (3) the Amundsen Sea Polynya (ASP), with high phytoplankton biomass dominated by Phaeocystis antarctica. Microzooplankton biomass and communities associated with phytoplankton biomass and composition varied among regions. Heterotrophic dinoflagellates (HDF) were the most significant grazers in the ASP and OZ, whereas ciliates co-dominated with HDF in the SIZ. Microzooplankton grazing impact is significant in our study area, particularly in the ASP, and consumed 55.4-107.6% of phytoplankton production (average 77.3%), with grazing impact increasing with prey and grazer biomass. This result implies that a significant proportion of the phytoplankton production is not removed by sinking or other grazers but grazed by microzooplankton. Compared with diatom-based systems, Phaeocystis-based production would be largely remineralized and/or channeled through the microbial food web through microzooplankton grazing. In these waters the major herbivorous fate of phytoplankton is likely mediated by the microzooplankton population. Our study confirms the importance of herbivorous protists in the planktonic ecosystems of high latitudes. In conclusion, microzooplankton herbivory may be a driving force controlling phytoplankton growth in early summer in the Amundsen Sea, particularly in the ASP.

  4. The Effect of Dilution on the Structure of Microbial Communities

    NASA Technical Reports Server (NTRS)

    Mills, Aaron L.

    2000-01-01

    To determine how dilution of microbial communities affects the diversity of the diluted assemblage a series of numerical simulations were conducted that determined the theoretical change in diversity, richness, and evenness of the community with serial dilution. The results of the simulation suggested that the effects are non linear with a high degree of dependence on the initial evenness of the community being diluted. A series of incubation experiments using a range of dilutions of raw sewage as an inoculum into sterile sewage was used for comparison to the simulations. The diluted communities were maintained in batch fed reactors (three day retention time) for nine days. The communities were harvested and examined by conventional plating and by molecular analysis of the whole-community DNA using AFLP and T-RFLP. Additional, CLPP analysis was also applied. The effects on richness predicted by the numerical simulations were confirmed by the analyses used. The diluted communities fell into three groups, a low dilution, intermediate dilution, and high dilution group, which corresponded well with the groupings obtained for community richness in simulation. The grouping demonstrated the non-linear nature of dilution of whole communities. Furthermore, the results implied that the undiluted community consisted of a few dominant types accompanied by a number of rare (low abundance) types as is typical in unevenly distributed communities.

  5. High Frequency Monitoring for Harmful Algal Blooms

    EPA Science Inventory

    Harmful algal blooms (HABs) are increasingly becoming a significant ecologic, economic, and social driver in the use of water resources. Cyanobacteria and their toxins play an important role in management decisions for drinking water utilities and public health officials. Online ...

  6. [Effect of environmental factors on fish community structure in the Huntai River Basin at multiple scales].

    PubMed

    Li, Yan-li; Li, Yan-fen; Xu, Zong-xue

    2014-09-01

    In June 2012, fishes was investigated at 65 sampling sites in the Huntai River basin in Northeast of China. Forty species were collected, belonging to 9 orders, 14 families,33 genera. Cobitidae and Cyprinidae were the dominant fishes in the community structure in the Huntai River basin, accounting for 13. 21% and 65. 83% of the fish community, respectively. There were two types of spatial distribution of fish community, one was distributed in the head water and tributaries in the upstream, and the other was in the plain rivers. Nemachilus nudus, Cobitis granoei and Phoxinus lagowskii dominated the local community in the upper reaches of the Dahuofang Reservoir and shenwo River, while Carassius ayratus and Hemiculter leucisculdus dominated the local community in the plain rivers. CCA (canonical correspondence analysis) was used to distinguish the primary environmental variables that affected the fish community structure. The results indicated fish community was mainly affected by environment factors at watershed and reach scales. Proportions of woodland and urban land, and altitude were three important environmental factors affecting the fish community at the watershed scale. Dissolved oxygen, total nitrogen, pH and habitat inhomogeneity significantly affected the fish community at the reach scale, whereas substrate didn't show significant influence at the microhabitat scale. Environmental factors at watershed scale explained 7. 66% of the variation of fish community structure, environmental factors at reach scale explained 10. 57% of the variation of fish community structure. Environmental factors at reach scale influenced the fish community more significantly. PMID:25518673

  7. Direct conversion of algal biomass to biofuel

    DOEpatents

    Deng, Shuguang; Patil, Prafulla D; Gude, Veera Gnaneswar

    2014-10-14

    A method and system for providing direct conversion of algal biomass. Optionally, the method and system can be used to directly convert dry algal biomass to biodiesels under microwave irradiation by combining the reaction and combining steps. Alternatively, wet algae can be directly processed and converted to fatty acid methyl esters, which have the major components of biodiesels, by reacting with methanol at predetermined pressure and temperature ranges.

  8. Hierarchical neighbor effects on mycorrhizal community structure and function.

    PubMed

    Moeller, Holly V; Dickie, Ian A; Peltzer, Duane A; Fukami, Tadashi

    2016-08-01

    Theory predicts that neighboring communities can shape one another's composition and function, for example, through the exchange of member species. However, empirical tests of the directionality and strength of these effects are rare. We determined the effects of neighboring communities on one another through experimental manipulation of a plant-fungal model system. We first established distinct ectomycorrhizal fungal communities on Douglas-fir seedlings that were initially grown in three soil environments. We then transplanted seedlings and mycorrhizal communities in a fully factorial experiment designed to quantify the direction and strength of neighbor effects by focusing on changes in fungal community species composition and implications for seedling growth (a proxy for community function). We found that neighbor effects on the composition and function of adjacent communities follow a dominance hierarchy. Specifically, mycorrhizal communities established from soils collected in Douglas-fir plantations were both the least sensitive to neighbor effects, and exerted the strongest influence on their neighbors by driving convergence in neighbor community composition and increasing neighbor seedling vigor. These results demonstrate that asymmetric neighbor effects mediated by ecological history can determine both community composition and function. PMID:27551393

  9. A Geospatial Analysis of Harmful Algal Blooms along the California Coast

    NASA Astrophysics Data System (ADS)

    Jensen, C.; Rothwell, R.; Johnson, E.; Condamoor, M.; Patil, M.; Largier, J. L.; Schmidt, C.

    2012-12-01

    Algal blooms are natural phenomena consisting of the rapid growth of phytoplankton populations. Some blooms have negative ecological or public health effects due to toxin production and removal of oxygen from the water column. In recent years, such "harmful algal blooms" (HABs) have been linked to human illness, economic loss from decreased fishing, and ecological damage related to marine life mortality as well as eutrophication. A notable HAB event occurred along the coast of northern California in August 2011, resulting in economic and ecological impacts of approximately $82 million. This was one of several algal blooms that occurred in fall 2011, with similar northward propagating algal blooms occurring in autumn of other years. Although the scale of the bloom impact is well-known, the spatial and temporal extent of the bloom boundary is still unclear. This study tracked the space-time pattern of numerous blooms during August-October 2011 using multiple NASA Earth observing systems in an effort to quantify and understand the structure of these recurrent bloom events. Aqua MODIS images were used to quantify surface chlorophyll-α levels, and thus to map the extent and development of all autumn algal blooms. The relation between sea surface temperature, ocean surface topography, and algal blooms was further explored with AVHRR and Jason-2 satellite data. A Generalized Additive Model (GAM) was used to identify the environmental factors most statistically influential in algal blooms and specifically in HAB events. Results from this study will assist California's Departments of Public Health and Fish & Game in mitigating and managing the impact of future harmful algal blooms.

  10. Textural variation within Great Salt Lake algal mounds: Chapter 8.5 in Stromatolites

    USGS Publications Warehouse

    1976-01-01

    This chapter discusses textural variation within the Great Salt Lake algal mounds. Great Salt Lake algal mounds contain: (1) a framework of non-skeletal, algally induced aragonite precipitates; (2) internal sediment; and (3) inorganic cement. These three elements create a variety of laminated, poorly laminated, and unlaminated internal textures. Interior framework precipitates bear little resemblance to the present living film of the mound surface. Internal texture of the mounds is believed to be largely relict and to have resulted from precipitation by algae different than those presently living at the surface. The most probable cause of local extinction of the algal flora is change in brine salinity. Precipitated blue-green algal structures in ancient rocks may indicate other than normal marine salinity and near shore sedimentation. Extreme variation of internal texture reflects extreme environmental variability typical of closed basin lakes. Recognition of mounds similar to those in the Great Salt Lake can be a first step toward recognition of ancient hyper-saline lake deposits, if such an interpretation is substantiated by consideration of the entire depositional milieu of precipitated algal mounds.

  11. Freshwater seepages and ephemeral macroalgae proliferation in an intertidal bay: I Effect on benthic community structure and food web

    NASA Astrophysics Data System (ADS)

    Ouisse, Vincent; Riera, Pascal; Migné, Aline; Leroux, Cédric; Davoult, Dominique

    2011-01-01

    Freshwater seepages and ephemeral Enteromorpha spp. proliferation create heterogeneity at small spatial scale in intertidal sediment. Macrobenthic community diversity was compared between these two disturbances and their respective control points throughout the year 2007 at the Roscoff Aber Bay (Western English Channel, France). In March and September 2007, trophic community pathways of characteristic species were additionally studied using stable isotope ratios of carbon and nitrogen. The low salinity recorded at the freshwater seepage induced the exclusion of the main bioturbator and the presence of omnivores which modified the community composition by biotic pressure. Moreover, food web analyses clearly highlighted a separation at small spatial scale between the two trophic pathways of the impacted area and its control. On the contrary, little differences were observed owning to the ephemeral Enteromorpha spp. proliferation. This suggested a progressive and diffusive disturbance which was applied from the algal mat to the nearby area. However, seasonal changes were observed. First, the algal expansion phase increased the macrofauna diversity and foraminifers' abundance (meiofauna) and then acted as a physical barrier decreasing sediment and water column exchanges and decreasing the fauna diversity. This study highlights the need to take into account small spatial heterogeneity to avoid misinterpretations in intertidal ecology studies.

  12. The ecology of rubble structures of the South Atlantic Bight: A community profile. [Jetties

    SciTech Connect

    Hay, M.E.; Sutherland, J.P.

    1988-09-01

    This community profile provides an introduction to the ecology of the communities living on and around rubble structures in the South Atlantic Bight (Cape Hatteras to Cape Canaveral). The most prominent rubble structures in the bight are jetties built at the entrances to major harbors. After an initial discussion of the various kinds of rubble structures and physical factors that affect the organisms associated with them, the major portion of the text is devoted to the ecology of rubble structure habitats. Community composition, distribution, seasonality, and the recruitment patterns of the major groups of organisms are described. The major physical and biological factors affecting the organization of intertidal, sunlit subtidal, and shaded subtidal communities are presented and the potential effects of complex interactions in structuring these communities are evaluated. The profile concludes with a general review of the effects of rubble structures on nearshore sediment dynamics and shoreline evolution. 295 refs., 33 figs., 4 tabs.

  13. Microflotation performance for algal separation.

    PubMed

    Hanotu, James; Bandulasena, H C Hemaka; Zimmerman, William B

    2012-07-01

    The performance of microflotation, dispersed air flotation with microbubble clouds with bubble size about 50 µm, for algae separation using fluidic oscillation for microbubble generation is investigated. This fluidic oscillator converts continuous air supply into oscillatory flow with a regular frequency to generate bubbles of the scale of the exit pore. Bubble characterization results showed that average bubble size generated under oscillatory air flow state was 86 µm, approximately twice the size of the diffuser pore size of 38 µm. In contrast, continuous air flow at the same rate through the same diffusers yielded an average bubble size of 1,059 µm, 28 times larger than the pore size. Following microbubble generation, the separation of algal cells under fluidic oscillator generated microbubbles was investigated by varying metallic coagulant types, concentration and pH. Best performances were recorded at the highest coagulant dose (150 mg/L) applied under acidic conditions (pH 5). Amongst the three metallic coagulants studied, ferric chloride yielded the overall best result of 99.2% under the optimum conditions followed closely by ferric sulfate (98.1%) and aluminum sulfate with 95.2%. This compares well with conventional dissolved air flotation (DAF) benchmarks, but has a highly turbulent flow, whereas microflotation is laminar with several orders of magnitude lower energy density. PMID:22290221

  14. Sterol phylogenesis and algal evolution

    SciTech Connect

    Nes, W.D.; Norton, R.A.; Crumley, F.G. ); Madigan, S.J.; Katz, E.R. )

    1990-10-01

    The stereochemistry of several sterol precursors and end products synthesized by two fungal-like microorganisms Prototheca wickerhamii (I) and Dictyostelium discoideum (II) have been determined by chromatographic (TLC, GLC, and HPLC) and spectral (UV, MS, and {sup 1}H NMR) methods. From I and II the following sterols were isolated from the cells: cycloartenol, cyclolaudenol, 24(28)-methylenecy-cloartanol, ergosterol, protothecasterol, 4{alpha}-methylergostanol, 4{alpha}-methylclionastanol, clionastanol, 24{beta}-ethylcholesta-8,22-enol, and dictyosterol. In addition, the mechanism of C-24 methylation was investigated in both organisms by feeding to I (2-{sup 3}H)lanosterol, (2-{sup 3}H)cycloartenol, (24{sup 3}H)lanosterol, and (methyl-{sup 2}H{sub 3})methionine and by feeding to II (methyl-{sup 2}H{sub 3})methionine. The results demonstrate that the 24{beta} configuration is formed by different alkylation routes in I and II. The authors conclude that Prototheca is an apoplastic Chlorella (i.e., an alga) and that Dictyostelium as well as the other soil amoebae that synthesize cycloartenol evolved from algal rather than fungal ancestors.

  15. Macroalgae Decrease Growth and Alter Microbial Community Structure of the Reef-Building Coral, Porites astreoides

    PubMed Central

    Vega Thurber, Rebecca; Burkepile, Deron E.; Correa, Adrienne M. S.; Thurber, Andrew R.; Shantz, Andrew A.; Welsh, Rory; Pritchard, Catharine; Rosales, Stephanie

    2012-01-01

    With the continued and unprecedented decline of coral reefs worldwide, evaluating the factors that contribute to coral demise is of critical importance. As coral cover declines, macroalgae are becoming more common on tropical reefs. Interactions between these macroalgae and corals may alter the coral microbiome, which is thought to play an important role in colony health and survival. Together, such changes in benthic macroalgae and in the coral microbiome may result in a feedback mechanism that contributes to additional coral cover loss. To determine if macroalgae alter the coral microbiome, we conducted a field-based experiment in which the coral Porites astreoides was placed in competition with five species of macroalgae. Macroalgal contact increased variance in the coral-associated microbial community, and two algal species significantly altered microbial community composition. All macroalgae caused the disappearance of a γ-proteobacterium previously hypothesized to be an important mutualist of P. astreoides. Macroalgal contact also triggered: 1) increases or 2) decreases in microbial taxa already present in corals, 3) establishment of new taxa to the coral microbiome, and 4) vectoring and growth of microbial taxa from the macroalgae to the coral. Furthermore, macroalgal competition decreased coral growth rates by an average of 36.8%. Overall, this study found that competition between corals and certain species of macroalgae leads to an altered coral microbiome, providing a potential mechanism by which macroalgae-coral interactions reduce coral health and lead to coral loss on impacted reefs. PMID:22957055

  16. Structure in Community College Career-Technical Programs: A Qualitative Analysis. CCRC Working Paper No. 50

    ERIC Educational Resources Information Center

    Van Noy, Michelle; Weiss, Madeline Joy; Jenkins, Davis; Barnett, Elisabeth A.; Wachen, John

    2012-01-01

    Using data obtained from interviews and program websites at Washington community and technical colleges, the authors of this study examine the structure of community college career-technical programs in allied health, business and marketing, computer and information studies, and mechanics and repair. A framework for structure with four…

  17. Algal Data from Selected Sites in the Upper Colorado River Basin, Colorado, Water Years 1996-97

    USGS Publications Warehouse

    Mize, Scott V.; Deacon, Jeffrey R.

    2001-01-01

    Algal community samples were collected at 15 sites in the Upper Colorado River Basin in Colorado as part of the National Water-Quality Assessment Program during water years 1996-97. Sites sampled were located in two physiographic provinces, the Southern Rocky Mountains and the Colorado Plateaus, and represented agricultural, mining, urban, and mixed land uses and background conditions. Algal samples were collected once per year during low-flow conditions. Quantitative algal samples were collected within two targeted instream habitat types including a taxonomically richest-targeted habitat and a depositional-targeted habitat. This report presents the algal community data collected at the fixed sites in the Upper Colorado River Basin study unit. Algal data include densities (abundance of cells per square centimeter of substrate) and biovolumes (cubic micrometers of cells per square centimeter of substrate) for the two habitat types. Quality-assurance and quality-control results for algal samples indicate that the largest sampling variability tends to occur in samples from small streams.

  18. [Community Structure of Aquatic Community and Evaluation of Water Quality in Laovingyan Section of Dadu River].

    PubMed

    Huang, You-you; Zeng, Yu; Liu, Shou-jiang; Ma, Yong-hong; Xu, Xiao

    2016-01-15

    In order to understand the aquatic community structure in the Laoyingyan section of the Dadu River, we collected samples from 9 aquatic sampling points along that section, and studied the phycophyta, zooplankton, benthic invertebrate and fish in them; we also used expert scoring method based on the actual situation of the river to weigh different biome. The water quality was evaluated using comprehensive evaluation of water quality index ( CEWI). The results showed that: (1) there were a total of 105 phycophyta species, belonging to 6 phyla,31 families, and 56 genera in the Laoyingyan section of the Dadu River, among which, diatom species had a higher richness than the others. The mean cell density of the phycophyta was 17.997 8 x 10(4) ind x L(-1), the mean biomass was 0.4463 mg x L(-1), and the highest population density sites were LTS, LYH and XSH. (2) there were a total of 26 zooplankton species, belonging to 3 phyla, 11 families, and 12 genera, among which, Protozoa had a higher richness than the others, accounting for 80.77% of all the zooplankton species; The mean density of the phycophyta was 40.89 ind x L(-1), and the mean biomass was 13.26 x 10(-3) mg x L(-1). The whole community composition was simple, characterized by few species and small population size. (3) there were a total of 14 benthic invertebrate species, belonging to 6 phyla,14 families, and 14 genera, among which, insecta had a higher richness than the others, accounting for 57.16% of the benthic invertebrate species. Benthic invertebrate had higher population densities in LYH and XSH. (4) The mean CEWI of the whole river water was 2. 698 28, characterized by slightly polluted water quality. The CEWI value between every collection point and the individual water quality evaluation index showed a significant positive correlation, manifesting a high consistency. In addition, the water quality of SLH and NYH was mesosaprobic (1 < CEWI < or = 2), and the water quality of LYH and LYY1 was clean

  19. The Structure and Process of School/Community Involvement.

    ERIC Educational Resources Information Center

    Miller, Michael Ronald

    The major problem of this study is that of identifying how schools function as both a determiner and a reflector of a society or community. It addresses three fundamental questions. First, access questions are dealt with, e.g. who participates--what is the position or social standing of community participants in schools. Second, process questions…

  20. The Effects of Structured Transfer Programs in Community Colleges

    ERIC Educational Resources Information Center

    Baker, Rachel

    2014-01-01

    Many community college students begin with the intention of transferring to a four-year school but relatively few actually do. One hypothesis for the low rates of successful two-to-four year transfers is that academic program choices in community colleges are too numerous and too complex. In this paper, the author will address a longer term…

  1. Algal Supply System Design - Harmonized Version

    SciTech Connect

    Abodeely, Jared; Stevens, Daniel; Ray, Allison; Newby, Deborah; Schaller, Kastli

    2013-03-01

    The objective of this design report is to provide an assessment of current technologies used for production, dewatering, and converting microalgae cultivated in open-pond systems to biofuel. The original draft design was created in 2011 and has subsequently been brought into agreement with the DOE harmonized model. The design report extends beyond this harmonized model to discuss some of the challenges with assessing algal production systems, including the ability to (1) quickly assess alternative algal production system designs, (2) assess spatial and temporal variability, and (3) perform large-scale assessments considering multiple scenarios for thousands of potential sites. The Algae Logistics Model (ALM) was developed to address each of these limitations of current modeling efforts to enable assessment of the economic feasibility of algal production systems across the United States. The (ALM) enables (1) dynamic assessments using spatiotemporal conditions, (2) exploration of algal production system design configurations, (3) investigation of algal production system operating assumptions, and (4) trade-off assessments with technology decisions and operating assumptions. The report discusses results from the ALM, which is used to assess the baseline design determined by harmonization efforts between U.S. DOE national laboratories. Productivity and resource assessment data is provided by coupling the ALM with the Biomass Assessment Tool developed at PNNL. This high-fidelity data is dynamically passed to the ALM and used to help better understand the impacts of spatial and temporal constraints on algal production systems by providing a cost for producing extracted algal lipids annually for each potential site.

  2. The Organization and Structure of Community Education Offerings in Community Colleges

    ERIC Educational Resources Information Center

    Miller, Michael; Grover, Kenda S.; Kacirek, Kit

    2014-01-01

    One of the key services community colleges provide is community education, meaning those programs and activities that are often offered for leisure or self-improvement and not for credit. Programs of this nature are increasingly challenged to be self-financing, whether through user fees or externally funded grants. The current study explored 75…

  3. Resources Alter the Structure and Increase Stochasticity in Bromeliad Microfauna Communities

    PubMed Central

    Petermann, Jana S.; Kratina, Pavel; Marino, Nicholas A. C.; MacDonald, A. Andrew M.; Srivastava, Diane S.

    2015-01-01

    Although stochastic and deterministic processes have been found to jointly shape structure of natural communities, the relative importance of both forces may vary across different environmental conditions and across levels of biological organization. We tested the effects of abiotic environmental conditions, altered trophic interactions and dispersal limitation on the structure of aquatic microfauna communities in Costa Rican tank bromeliads. Our approach combined natural gradients in environmental conditions with experimental manipulations of bottom-up interactions (resources), top-down interactions (predators) and dispersal at two spatial scales in the field. We found that resource addition strongly increased the abundance and reduced the richness of microfauna communities. Community composition shifted in a predictable way towards assemblages dominated by flagellates and ciliates but with lower abundance and richness of algae and amoebae. While all functional groups responded strongly and predictably to resource addition, similarity among communities at the species level decreased, suggesting a role of stochasticity in species-level assembly processes. Dispersal limitation did not affect the communities. Since our design excluded potential priority effects we can attribute the differences in community similarity to increased demographic stochasticity of resource-enriched communities related to erratic changes in population sizes of some species. In contrast to resources, predators and environmental conditions had negligible effects on community structure. Our results demonstrate that bromeliad microfauna communities are strongly controlled by bottom-up forces. They further suggest that the relative importance of stochasticity may change with productivity and with the organizational level at which communities are examined. PMID:25775464

  4. Resources alter the structure and increase stochasticity in bromeliad microfauna communities.

    PubMed

    Petermann, Jana S; Kratina, Pavel; Marino, Nicholas A C; MacDonald, A Andrew M; Srivastava, Diane S

    2015-01-01

    Although stochastic and deterministic processes have been found to jointly shape structure of natural communities, the relative importance of both forces may vary across different environmental conditions and across levels of biological organization. We tested the effects of abiotic environmental conditions, altered trophic interactions and dispersal limitation on the structure of aquatic microfauna communities in Costa Rican tank bromeliads. Our approach combined natural gradients in environmental conditions with experimental manipulations of bottom-up interactions (resources), top-down interactions (predators) and dispersal at two spatial scales in the field. We found that resource addition strongly increased the abundance and reduced the richness of microfauna communities. Community composition shifted in a predictable way towards assemblages dominated by flagellates and ciliates but with lower abundance and richness of algae and amoebae. While all functional groups responded strongly and predictably to resource addition, similarity among communities at the species level decreased, suggesting a role of stochasticity in species-level assembly processes. Dispersal limitation did not affect the communities. Since our design excluded potential priority effects we can attribute the differences in community similarity to increased demographic stochasticity of resource-enriched communities related to erratic changes in population sizes of some species. In contrast to resources, predators and environmental conditions had negligible effects on community structure. Our results demonstrate that bromeliad microfauna communities are strongly controlled by bottom-up forces. They further suggest that the relative importance of stochasticity may change with productivity and with the organizational level at which communities are examined. PMID:25775464

  5. EFFECTS OF SEDIMENT CONTAMINANTS AND ENVIRONMENTAL GRADIENTS ON MACROBENTHIC COMMUNITY TROPHIC STRUCTURE IN GULF OF MEXICO ESTUARIES

    EPA Science Inventory

    Macrobenthic communities from estuaries throughout the northern Gulf of Mexico were studied to assess the influence of sediment contaminants and natural environmental factors on macrobenthic community trophic structure. Community trophic data were also used to evaluate whether re...

  6. Unusual bacterioplankton community structure in ultra-oligotrophic Crater Lake

    USGS Publications Warehouse

    Urbach, Ena; Vergin, Kevin L.; Morse, Ariel

    2001-01-01

    The bacterioplankton assemblage in Crater Lake, Oregon (U.S.A.), is different from communities found in other oxygenated lakes, as demonstrated by four small subunit ribosomal ribonucleic acid (SSU rRNA) gene clone libraries and oligonucleotide probe hybridization to RNA from lake water. Populations in the euphotic zone of this deep (589 m), oligotrophic caldera lake are dominated by two phylogenetic clusters of currently uncultivated bacteria: CL120-10, a newly identified cluster in the verrucomicrobiales, and ACK4 actinomycetes, known as a minor constituent of bacterioplankton in other lakes. Deep-water populations at 300 and 500 m are dominated by a different pair of uncultivated taxa: CL500-11, a novel cluster in the green nonsulfur bacteria, and group I marine crenarchaeota. b-Proteobacteria, dominant in most other freshwater environments, are relatively rare in Crater Lake (<=16% of nonchloroplast bacterial rRNA at all depths). Other taxa identified in Crater Lake libraries include a newly identified candidate bacterial division, ABY1, and a newly identified subcluster, CL0-1, within candidate division OP10. Probe analyses confirmed vertical stratification of several microbial groups, similar to patterns observed in open-ocean systems. Additional similarities between Crater Lake and ocean microbial populations include aphotic zone dominance of group I marine crenarchaeota and green nonsulfur bacteria. Comparison of Crater Lake to other lakes studied by rRNA methods suggests that selective factors structuring Crater Lake bacterioplankton populations may include low concentrations of available trace metals and dissolved organic matter, chemistry of infiltrating hydrothermal waters, and irradiation by high levels of ultraviolet light.

  7. Algal Energy Conversion and Capture

    NASA Astrophysics Data System (ADS)

    Hazendonk, P.

    2015-12-01

    We address the potential for energy conversions and capture for: energy generation; reduction in energy use; reduction in greenhouse gas emissions; remediation of water and air pollution; protection and enhancement of soil fertility. These processes have the potential to sequester carbon at scales that may have global impact. Energy conversion and capture strategies evaluate energy use and production from agriculture, urban areas and industries, and apply existing and emerging technologies to reduce and recapture energy embedded in waste products. The basis of biocrude production from Micro-algal feedstocks: 1) The nutrients from the liquid fraction of waste streams are concentrated and fed into photo bioreactors (essentially large vessels in which microalgae are grown) along with CO2 from flue gasses from down stream processes. 2) The algae are processed to remove high value products such as proteins and beta-carotenes. The advantage of algae feedstocks is the high biomass productivity is 30-50 times that of land based crops and the remaining biomass contains minimal components that are difficult to convert to biocrude. 3) The remaining biomass undergoes hydrothermal liquefaction to produces biocrude and biochar. The flue gasses of this process can be used to produce electricity (fuel cell) and subsequently fed back into the photobioreactor. The thermal energy required for this process is small, hence readily obtained from solar-thermal sources, and furthermore no drying or preprocessing is required keeping the energy overhead extremely small. 4) The biocrude can be upgraded and refined as conventional crude oil, creating a range of liquid fuels. In principle this process can be applied on the farm scale to the municipal scale. Overall, our primary food production is too dependent on fossil fuels. Energy conversion and capture can make food production sustainable.

  8. Supraglacial bacterial community structures vary across the Greenland ice sheet.

    PubMed

    Cameron, Karen A; Stibal, Marek; Zarsky, Jakub D; Gözdereliler, Erkin; Schostag, Morten; Jacobsen, Carsten S

    2016-02-01

    The composition and spatial variability of microbial communities that reside within the extensive (>200 000 km(2)) biologically active area encompassing the Greenland ice sheet (GrIS) is hypothesized to be variable. We examined bacterial communities from cryoconite debris and surface ice across the GrIS, using sequence analysis and quantitative PCR of 16S rRNA genes from co-extracted DNA and RNA. Communities were found to differ across the ice sheet, with 82.8% of the total calculated variation attributed to spatial distribution on a scale of tens of kilometers separation. Amplicons related to Sphingobacteriaceae, Pseudanabaenaceae and WPS-2 accounted for the greatest portion of calculated dissimilarities. The bacterial communities of ice and cryoconite were moderately similar (global R = 0.360, P = 0.002) and the sampled surface type (ice versus cryoconite) did not contribute heavily towards community dissimilarities (2.3% of total variability calculated). The majority of dissimilarities found between cryoconite 16S rRNA gene amplicons from DNA and RNA was calculated to be the result of changes in three taxa, Pseudanabaenaceae, Sphingobacteriaceae and WPS-2, which together contributed towards 80.8 ± 12.6% of dissimilarities between samples. Bacterial communities across the GrIS are spatially variable active communities that are likely influenced by localized biological inputs and physicochemical conditions. PMID:26691594

  9. Assembly of forest communities across East Asia – insights from phylogenetic community structure and species pool scaling

    PubMed Central

    Feng, Gang; Mi, Xiangcheng; Eiserhardt, Wolf L.; Jin, Guangze; Sang, Weiguo; Lu, Zhijun; Wang, Xihua; Li, Xiankun; Li, Buhang; Sun, Ifang; Ma, Keping; Svenning, Jens-Christian

    2015-01-01

    Local communities are assembled from larger-scale species pools via dispersal, environmental filtering, biotic interactions, and local stochastic demographic processes. The relative importance, scaling and interplay of these assembly processes can be elucidated by comparing local communities to variously circumscribed species pools. Here we present the first study applying this approach to forest tree communities across East Asia, focusing on community phylogenetic structure and using data from a global network of tropical, subtropical and temperate forest plots. We found that Net Relatedness Index (NRI) and Nearest Taxon Index (NTI) values were generally lower with geographically broad species pools (global and Asian species pools) than with an East Asian species pool, except that global species pool produced higher NTI than the East Asian species pool. The lower NRI for the global relative to the East Asian species pool may indicate an important role of intercontinental migration during the Neogene and Quaternary and climatic conservatism in shaping the deeper phylogenetic structure of tree communities in East Asia. In contrast, higher NTI for the global relative to the East Asian species pool is consistent with recent localized diversification determining the shallow phylogenetic structure. PMID:25797420

  10. Assembly of forest communities across East Asia--insights from phylogenetic community structure and species pool scaling.

    PubMed

    Feng, Gang; Mi, Xiangcheng; Eiserhardt, Wolf L; Jin, Guangze; Sang, Weiguo; Lu, Zhijun; Wang, Xihua; Li, Xiankun; Li, Buhang; Sun, Ifang; Ma, Keping; Svenning, Jens-Christian

    2015-01-01

    Local communities are assembled from larger-scale species pools via dispersal, environmental filtering, biotic interactions, and local stochastic demographic processes. The relative importance, scaling and interplay of these assembly processes can be elucidated by comparing local communities to variously circumscribed species pools. Here we present the first study applying this approach to forest tree communities across East Asia, focusing on community phylogenetic structure and using data from a global network of tropical, subtropical and temperate forest plots. We found that Net Relatedness Index (NRI) and Nearest Taxon Index (NTI) values were generally lower with geographically broad species pools (global and Asian species pools) than with an East Asian species pool, except that global species pool produced higher NTI than the East Asian species pool. The lower NRI for the global relative to the East Asian species pool may indicate an important role of intercontinental migration during the Neogene and Quaternary and climatic conservatism in shaping the deeper phylogenetic structure of tree communities in East Asia. In contrast, higher NTI for the global relative to the East Asian species pool is consistent with recent localized diversification determining the shallow phylogenetic structure. PMID:25797420

  11. Among-habitat algal selectivity by browsing herbivores on an inshore coral reef

    NASA Astrophysics Data System (ADS)

    Loffler, Zoe; Bellwood, David R.; Hoey, Andrew S.

    2015-06-01

    Understanding how the impact of different herbivores varies spatially on coral reefs is important in qualifying the resistance of coral reefs to disturbance events and identifying the processes that structure algal communities. We used assays of six common macroalgae ( Acanthophora spicifera, Caulerpa taxifolia, Galaxaura rugosa, Laurencia sp. Sargassum sp., and Turbinaria ornata) and remote underwater video cameras to quantify herbivory in two habitats (reef crest and slope) across multiple sites on Orpheus Island, Great Barrier Reef. Rates of herbivory varied among macroalgal taxa, habitats, and sites. Reductions in algal biomass were greatest for Sargassum sp. (36 % 4 h-1), intermediate for A. spicifera, Laurencia sp., C. taxifolia, and T. ornata (17-33 % 4 h-1) and lowest for G. rugosa (6 % 4 h-1). Overall, rates of herbivory were generally greater on the reef crest (30 % 4 h-1) than the reef slope (21 % 4 h-1). This difference in rates of herbivory coincided with a marked shift in the dominant herbivores between habitats. Kyphosus vaigiensis, despite only feeding on three species of macroalgae ( Sargassum sp., T. ornata, and A. spicifera), was responsible for 34 % of all bites recorded on the reef crest yet did not take a single bite from algae on the reef slope. In contrast, Siganus doliatus took bites on every species of algae in both habitats, accounting for 40 % of bites on the reef crest and 74 % of all bites recorded on the reef slope. This difference in the number of macroalgal species targeted by herbivores and the habitat/s in which they feed adds another dimension of complexity to our understanding of coral reef herbivore dynamics.

  12. Light Structures Phototroph, Bacterial and Fungal Communities at the Soil Surface

    PubMed Central

    Davies, Lawrence O.; Schäfer, Hendrik; Marshall, Samantha; Bramke, Irene; Oliver, Robin G.; Bending, Gary D.

    2013-01-01

    The upper few millimeters of soil harbour photosynthetic microbial communities that are structurally distinct from those of underlying bulk soil due to the presence of light. Previous studies in arid zones have demonstrated functional importance of these communities in reducing soil erosion, and enhancing carbon and nitrogen fixation. Despite being widely distributed, comparative understanding of the biodiversity of the soil surface and underlying soil is lacking, particularly in temperate zones. We investigated the establishment of soil surface communities on pasture soil in microcosms exposed to light or dark conditions, focusing on changes in phototroph, bacterial and fungal communities at the soil surface (0–3 mm) and bulk soil (3–12 mm) using ribosomal marker gene analyses. Microbial community structure changed with time and structurally similar phototrophic communities were found at the soil surface and in bulk soil in the light exposed microcosms suggesting that light can influence phototroph community structure even in the underlying bulk soil. 454 pyrosequencing showed a significant selection for diazotrophic cyanobacteria such as Nostoc punctiforme and Anabaena spp., in addition to the green alga Scenedesmus obliquus. The soil surface also harboured distinct heterotrophic bacterial and fungal communities in the presence of light, in particular, the selection for the phylum Firmicutes. However, these light driven changes in bacterial community structure did not extend to the underlying soil suggesting a discrete zone of influence, analogous to the rhizosphere. PMID:23894406

  13. Platy algal banks: Modern and ancient

    SciTech Connect

    Brinton, L. )

    1990-05-01

    Plaly algal banks and associated cycles in the lower Ismay zone of the Paradox Formation are exposed along the walls of the San Juan River canyon, southeastern Utah. These complexes closely resemble algal bank reservoirs in the lower Ismay zone of Ismay and Cache, and possibly other Paradox basin fields. Similarities include facies relationships, lateral and vertical textural variations, and early diagenesis. Extensive algal banks exposed along the San Juan canyon generally have flat bases and mound and swale topographic surfaces, and are separated by interbank channels. The surficial mounds have a regular amplitude and wavelength suggesting a hydrologic rather than biologic influence on topography. The banks themselves, however, are believed to be thick, predominantly in-situ accumulations of platy algae. Distribution of algal banks can be mapped on a field scale; mound and swale topographic features may be identified in core on the basis of depositional and early diagenetic characteristics. Halimeda bioherms (Holocene) cover large areas behind the Great Barrier Reef, developing adjacent to the deep passes that separate the individual reefs. These large in-situ accumulations (20-50 m deep) display similar bank geometries, interbank features, topographic features, vertical textural sequence (including porosity type and distribution), and facies relationships to algal banks observed in the outcropping and subsurface Paradox Formation. Although the hydrodynamic and paleobathymetric settings differ markedly between these two examples, analogies between the mounds themselves are very close. The resemblance lends relevance to exploration and development drilling.

  14. Structure and function of fish communities in the southern Lake Michigan basin with emphasis on restoration of native fish communities

    USGS Publications Warehouse

    Simon, Thomas P.; Stewart, Paul M.

    1999-01-01

    The southern Lake Michigan basin in northwest Indiana possesses a variety of aquatic habitats including riverine, palustrine, and lacustrine systems. The watershed draining this area is a remnant of glacial Lake Chicago and supports fish communities that are typically low in species richness. Composition of the presettlement Lake Michigan fish community near the Indiana Dunes has been difficult to reconstruct. Existing data indicate that the number of native species in the Lake Michigan watershed, including nearshore Lake Michigan, has declined by 22% since the onset of European settlement. Few remnants of natural fish communities exist, and those occur principally in the ponds of Miller Woods, the Grand Calumet Lagoons, and the Little Calumet River. These communities have maintained a relatively diverse assemblage of fishes despite large-scale anthropogenic disturbances in the area, including channelization, massive river redirection, fragmentation, habitat alteration, exotic species invasions, and the introduction of toxic chemicals. Data that we collected from 1985 to 1996 suggested that the Grand Calumet River has the highest proportion of exotic fish species of any inland wetland in northwest Indiana. Along the Lake Michigan shoreline, another group of exotics (e.g., round goby, alewife, and sea lamprey) have affected the structure of native fish communities, thereby altering lake ecosystem function. Stocking programs contribute to the impairment of native communities. Nonindigenous species have restructured the function of Lake Michigan tributaries, causing disruptions in trophic dynamics, guild structure, and species diversity. Several fish communities have been reduced or eliminated by the alteration and destruction of spawning and nursery areas. Degradation of habitats has caused an increase in numbers and populations of species able to tolerate and flourish when confronted with hydrologic alteration. Fish communities found on public lands in northwest

  15. Cooperation and punishment in community-structured populations with migration.

    PubMed

    Kaiping, G A; Cox, S J; Sluckin, T J

    2016-09-21

    The stable presence of punishing strategies in various cooperative species is a persistent puzzle in the study of the evolution of cooperation. To investigate the effect of group competition, we study the evolutionary dynamics of the Public Goods Game with punishment in a metapopulation that consists of separate communities. In addition to (a) well-mixed non-interacting communities, we model three distinct types of interaction between communities, (b) Migration independent of fitness; (c) Competition between whole communities, where entire communities replace each other depending on average fitness; (d) Migration where the probability of an offspring replacing an individual in another community depends on fitness. We use stochastic simulations to study the long-run frequencies of strategies with these interactions, subject to high mutation and migration rates. In cases (a) and (b), the transition between cooperation/punishment and defection regimes occurs for similar parameter values; with migration (b), the transitions are steeper due to higher total mixing. Fitness-based migration (d) by contrast can help support cooperation, changing the locations of transitions, but while group selection (c) does stabilise cooperation over much of the parameter space, fitness-based migration (d) acts as a proxy for group selection only in a smaller region. PMID:26796223

  16. Impact of metal pollution on fungal diversity and community structures.

    PubMed

    Op De Beeck, Michiel; Lievens, Bart; Busschaert, Pieter; Rineau, Francois; Smits, Mark; Vangronsveld, Jaco; Colpaert, Jan V

    2015-06-01

    The impact of metal pollution on plant communities has been studied extensively in the past, but little is known about the effects of metal pollution on fungal communities that occur in metal-polluted soils. Metal-tolerant ecotypes of the ectomycorrhizal fungus Suillus luteus are frequently found in pioneer pine forests in the Campine region in Belgium on metal-polluted soils. We hypothesized that metal pollution would play an important role in shaping below-ground fungal communities that occur in these soils and that Suillus luteus would be a dominant player. To test these hypotheses, the fungal communities in a young pine plantation in soil polluted with zinc, and cadmium were studied using 454 amplicon pyrosequencing. Results show that zinc, cadmium and soil organic matter content were strongly correlated with the fungal community composition, but no effects on fungal diversity were observed. As hypothesized, S. luteus was found to be a dominant member of the studied fungal communities. However, other dominant fungal species, such as Sistotrema sp., Wilcoxina mikolae and Cadophora finlandica were found as well. Their presence in metal-polluted sites is discussed. PMID:24947496

  17. Overlapping communities reveal rich structure in large-scale brain networks during rest and task conditions.

    PubMed

    Najafi, Mahshid; McMenamin, Brenton W; Simon, Jonathan Z; Pessoa, Luiz

    2016-07-15

    Large-scale analysis of functional MRI data has revealed that brain regions can be grouped into stable "networks" or communities. In many instances, the communities are characterized as relatively disjoint. Although recent work indicates that brain regions may participate in multiple communities (for example, hub regions), the extent of community overlap is poorly understood. To address these issues, here we investigated large-scale brain networks based on "rest" and task human functional MRI data by employing a mixed-membership Bayesian model that allows each brain region to belong to all communities simultaneously with varying membership strengths. The approach allowed us to 1) compare the structure of disjoint and overlapping communities; 2) determine the relationship between functional diversity (how diverse is a region's functional activation repertoire) and membership diversity (how diverse is a region's affiliation to communities); 3) characterize overlapping community structure; 4) characterize the degree of non-modularity in brain networks; 5) study the distribution of "bridges", including bottleneck and hub bridges. Our findings revealed the existence of dense community overlap that was not limited to "special" hubs. Furthermore, the findings revealed important differences between community organization during rest and during specific task states. Overall, we suggest that dense overlapping communities are well suited to capture the flexible and task dependent mapping between brain regions and their functions. PMID:27129758

  18. Critical evaluation and modeling of algal harvesting using dissolved air flotation. DAF Algal Harvesting Modeling

    DOE PAGESBeta

    Zhang, Xuezhi; Hewson, John C.; Amendola, Pasquale; Reynoso, Monica; Sommerfeld, Milton; Chen, Yongsheng; Hu, Qiang

    2014-07-14

    In our study, Chlorella zofingiensis harvesting by dissolved air flotation (DAF) was critically evaluated with regard to algal concentration, culture conditions, type and dosage of coagulants, and recycle ratio. Harvesting efficiency increased with coagulant dosage and leveled off at 81%, 86%, 91%, and 87% when chitosan, Al3+, Fe3+, and cetyl trimethylammonium bromide (CTAB) were used at dosages of 70, 180, 250, and 500 mg g-1, respectively. The DAF efficiency-coagulant dosage relationship changed with algal culture conditions. In evaluating the influence of the initial algal concentration and recycle ratio revealed that, under conditions typical for algal harvesting, we found that itmore » is possible that the number of bubbles is insufficient. A DAF algal harvesting model was developed to explain this observation by introducing mass-based floc size distributions and a bubble limitation into the white water blanket model. Moreover, the model revealed the importance of coagulation to increase floc-bubble collision and attachment, and the preferential interaction of bubbles with larger flocs, which limited the availability of bubbles to the smaller sized flocs. The harvesting efficiencies predicted by the model agree reasonably with experimental data obtained at different Al3+ dosages, algal concentrations, and recycle ratios. Based on this modeling, critical parameters for efficient algal harvesting were identified.« less

  19. Critical evaluation and modeling of algal harvesting using dissolved air flotation. DAF Algal Harvesting Modeling

    SciTech Connect

    Zhang, Xuezhi; Hewson, John C.; Amendola, Pasquale; Reynoso, Monica; Sommerfeld, Milton; Chen, Yongsheng; Hu, Qiang

    2014-07-14

    In our study, Chlorella zofingiensis harvesting by dissolved air flotation (DAF) was critically evaluated with regard to algal concentration, culture conditions, type and dosage of coagulants, and recycle ratio. Harvesting efficiency increased with coagulant dosage and leveled off at 81%, 86%, 91%, and 87% when chitosan, Al3+, Fe3+, and cetyl trimethylammonium bromide (CTAB) were used at dosages of 70, 180, 250, and 500 mg g-1, respectively. The DAF efficiency-coagulant dosage relationship changed with algal culture conditions. In evaluating the influence of the initial algal concentration and recycle ratio revealed that, under conditions typical for algal harvesting, we found that it is possible that the number of bubbles is insufficient. A DAF algal harvesting model was developed to explain this observation by introducing mass-based floc size distributions and a bubble limitation into the white water blanket model. Moreover, the model revealed the importance of coagulation to increase floc-bubble collision and attachment, and the preferential interaction of bubbles with larger flocs, which limited the availability of bubbles to the smaller sized flocs. The harvesting efficiencies predicted by the model agree reasonably with experimental data obtained at different Al3+ dosages, algal concentrations, and recycle ratios. Based on this modeling, critical parameters for efficient algal harvesting were identified.

  20. Priming in the microbial landscape: periphytic algal stimulation of litter-associated microbial decomposers.

    PubMed

    Kuehn, Kevin A; Francoeur, Steven N; Findlay, Robert H; Neely, Robert K

    2014-03-01

    Microbial communities associated with submerged detritus in aquatic ecosystems often comprise a diverse mixture of autotrophic and heterotrophic microbes, including algae, bacteria, protozoa, and fungi. Recent studies have documented increased rates of plant litter mass loss when periphytic algae are present. We conducted laboratory and field experiments to assess potential metabolic interactions between natural autotrophic and heterotrophic microbial communities inhabiting submerged decaying plant litter of Typha angustifolia and Schoenoplectus acutus. In the field, submerged plant litter was either exposed to natural sunlight or placed under experimental canopies that manipulated light availability and growth of periphytic algae. Litter was collected and returned to the laboratory, where algal photosynthesis was manipulated (light/dark incubation), while rates of bacterial and fungal growth and productivity were simultaneously quantified. Bacteria and fungi were rapidly stimulated by exposure to light, thus establishing the potential for algal priming of microbial heterotrophic decay activities. Experimental incubations of decaying litter with 14C- and 13C-bicarbonate established that inorganic C fixed by algal photosynthesis was rapidly transferred to and assimilated by heterotrophic microbial decomposers. Periphytic algal stimulation of microbial heterotrophs, especially fungal decomposers, is an important and largely unrecognized interaction within the detrital microbial landscape, which may transform our current conceptual understanding of microbial secondary production and organic matter decomposition in aquatic ecosystems. PMID:24804458

  1. Industrial-strength ecology: trade-offs and opportunities in algal biofuel production.

    PubMed

    Shurin, Jonathan B; Abbott, Rachel L; Deal, Michael S; Kwan, Garfield T; Litchman, Elena; McBride, Robert C; Mandal, Shovon; Smith, Val H

    2013-11-01

    Microalgae represent one of the most promising groups of candidate organisms for replacing fossil fuels with contemporary primary production as a renewable source of energy. Algae can produce many times more biomass per unit area than terrestrial crop plants, easing the competing demands for land with food crops and native ecosystems. However, several aspects of algal biology present unique challenges to the industrial-scale aquaculture of photosynthetic microorganisms. These include high susceptibility to invading aquatic consumers and weeds, as well as prodigious requirements for nutrients that may compete with the fertiliser demands of other crops. Most research on algal biofuel technologies approaches these problems from a cellular or genetic perspective, attempting either to engineer or select algal strains with particular traits. However, inherent functional trade-offs may limit the capacity of genetic selection or synthetic biology to simultaneously optimise multiple functional traits for biofuel productivity and resilience. We argue that a community engineering approach that manages microalgal diversity, species composition and environmental conditions may lead to more robust and productive biofuel ecosystems. We review evidence for trade-offs, challenges and opportunities in algal biofuel cultivation with a goal of guiding research towards intensifying bioenergy production using established principles of community and ecosystem ecology. PMID:24015819

  2. Growth of Heterotrophic Bacteria and Algal Extracellular Products in Oligotrophic Waters

    PubMed Central

    McFeters, Gordon A.; Stuart, Sidney A.; Olson, Susan B.

    1978-01-01

    The unexpected observation of 200 to 400 coliform bacteria per 100 ml in an unpolluted pristine stream was studied within Grand Teton National Park, Wyo. The high numbers of waterborne bacteria occurred in mid- to late summer at a location where there was a coincidental bloom of an algal mat community. Periphyton samplers were used to measure the algal growth that coincided with the increase in number of bacteria. Laboratory studies followed the growth of various coliform bacteria in the supernatant obtained from a Chlorella culture isolated from the mat community. Mixed natural bacterial populations from the stream and pure cultures of water-isolated fecal and nonfecal coliforms increased by two to three orders of magnitude at 13°C when grown in the algal supernatant. Radioactive algal products were obtained by feeding an axenic Chlorella culture 14C-labeled bicarbonate under laboratory cultivation at 13°C with illumination. Radioactive organic material from the algae became incorporated into the particulate fraction of pure cultures of coliform bacteria as they reproduced and was later released as they died. PMID:16345278

  3. Microbes as Engines of Ecosystem Function: When Does Community Structure Enhance Predictions of Ecosystem Processes?

    PubMed

    Graham, Emily B; Knelman, Joseph E; Schindlbacher, Andreas; Siciliano, Steven; Breulmann, Marc; Yannarell, Anthony; Beman, J M; Abell, Guy; Philippot, Laurent; Prosser, James; Foulquier, Arnaud; Yuste, Jorge C; Glanville, Helen C; Jones, Davey L; Angel, Roey; Salminen, Janne; Newton, Ryan J; Bürgmann, Helmut; Ingram, Lachlan J; Hamer, Ute; Siljanen, Henri M P; Peltoniemi, Krista; Potthast, Karin; Bañeras, Lluís; Hartmann, Martin; Banerjee, Samiran; Yu, Ri-Qing; Nogaro, Geraldine; Richter, Andreas; Koranda, Marianne; Castle, Sarah C; Goberna, Marta; Song, Bongkeun; Chatterjee, Amitava; Nunes, Olga C; Lopes, Ana R; Cao, Yiping; Kaisermann, Aurore; Hallin, Sara; Strickland, Michael S; Garcia-Pausas, Jordi; Barba, Josep; Kang, Hojeong; Isobe, Kazuo; Papaspyrou, Sokratis; Pastorelli, Roberta; Lagomarsino, Alessandra; Lindström, Eva S; Basiliko, Nathan; Nemergut, Diana R

    2016-01-01

    Microorganisms are vital in mediating the earth's biogeochemical cycles; yet, despite our rapidly increasing ability to explore complex environmental microbial communities, the relationship between microbial community structure and ecosystem processes remains poorly understood. Here, we address a fundamental and unanswered question in microbial ecology: 'When do we need to understand microbial community structure to accurately predict function?' We present a statistical analysis investigating the value of environmental data and microbial community structure independently and in combination for explaining rates of carbon and nitrogen cycling processes within 82 global datasets. Environmental variables were the strongest predictors of process rates but left 44% of variation unexplained on average, suggesting the potential for microbial data to increase model accuracy. Although only 29% of our datasets were significantly improved by adding information on microbial community structure, we observed improvement in models of processes mediated by narrow phylogenetic guilds via functional gene data, and conversely, improvement in models of facultative microbial processes via community diversity metrics. Our results also suggest that microbial diversity can strengthen predictions of respiration rates beyond microbial biomass parameters, as 53% of models were improved by incorporating both sets of predictors compared to 35% by microbial biomass alone. Our analysis represents the first comprehensive analysis of research examining links between microbial community structure and ecosystem function. Taken together, our results indicate that a greater understanding of microbial communities informed by ecological principles may enhance our ability to predict ecosystem process rates relative to assessments based on environmental variables and microbial physiology. PMID:26941732

  4. The reconstruction of complex networks with community structure

    PubMed Central

    Zhang, Peng; Wang, Futian; Wang, Xiang; Zeng, An; Xiao, Jinghua

    2015-01-01

    Link prediction is a fundamental problem with applications in many fields ranging from biology to computer science. In the literature, most effort has been devoted to estimate the likelihood of the existence of a link between two nodes, based on observed links and nodes’ attributes in a network. In this paper, we apply several representative link prediction methods to reconstruct the network, namely to add the missing links with high likelihood of existence back to the network. We find that all these existing methods fail to identify the links connecting different communities, resulting in a poor reproduction of the topological and dynamical properties of the true network. To solve this problem, we propose a community-based link prediction method. We find that our method has high prediction accuracy and is very effective in reconstructing the inter-community links. PMID:26620158

  5. The reconstruction of complex networks with community structure

    NASA Astrophysics Data System (ADS)

    Zhang, Peng; Wang, Futian; Wang, Xiang; Zeng, An; Xiao, Jinghua

    2015-12-01

    Link prediction is a fundamental problem with applications in many fields ranging from biology to computer science. In the literature, most effort has been devoted to estimate the likelihood of the existence of a link between two nodes, based on observed links and nodes’ attributes in a network. In this paper, we apply several representative link prediction methods to reconstruct the network, namely to add the missing links with high likelihood of existence back to the network. We find that all these existing methods fail to identify the links connecting different communities, resulting in a poor reproduction of the topological and dynamical properties of the true network. To solve this problem, we propose a community-based link prediction method. We find that our method has high prediction accuracy and is very effective in reconstructing the inter-community links.

  6. Geochip: A high throughput genomic tool for linking community structure to functions

    SciTech Connect

    Van Nostrand, Joy D.; Liang, Yuting; He, Zhili; Li, Guanghe; Zhou, Jizhong

    2009-01-30

    GeoChip is a comprehensive functional gene array that targets key functional genes involved in the geochemical cycling of N, C, and P, sulfate reduction, metal resistance and reduction, and contaminant degradation. Studies have shown the GeoChip to be a sensitive, specific, and high-throughput tool for microbial community analysis that has the power to link geochemical processes with microbial community structure. However, several challenges remain regarding the development and applications of microarrays for microbial community analysis.

  7. Alien Marine Fishes Deplete Algal Biomass in the Eastern Mediterranean

    PubMed Central

    Sala, Enric; Kizilkaya, Zafer; Yildirim, Derya; Ballesteros, Enric

    2011-01-01

    One of the most degraded states of the Mediterranean rocky infralittoral ecosystem is a barren composed solely of bare rock and patches of crustose coralline algae. Barrens are typically created by the grazing action of large sea urchin populations. In 2008 we observed extensive areas almost devoid of erect algae, where sea urchins were rare, on the Mediterranean coast of Turkey. To determine the origin of those urchin-less ‘barrens’, we conducted a fish exclusion experiment. We found that, in the absence of fish grazing, a well-developed algal assemblage grew within three months. Underwater fish censuses and observations suggest that two alien herbivorous fish from the Red Sea (Siganus luridus and S. rivulatus) are responsible for the creation and maintenance of these benthic communities with extremely low biomass. The shift from well-developed native algal assemblages to ‘barrens’ implies a dramatic decline in biogenic habitat complexity, biodiversity and biomass. A targeted Siganus fishery could help restore the macroalgal beds of the rocky infralittoral on the Turkish coast. PMID:21364943

  8. Can artificial reefs mimic natural reef communities? The roles of structural features and age.

    PubMed

    Perkol-Finkel, S; Shashar, N; Benayahu, Y

    2006-03-01

    In light of the deteriorating state of coral reefs worldwide, the need to rehabilitate marine environments has greatly increased. Artificial reefs (ARs) have been suggested as a tool for reef conservation and rehabilitation. Although successions of AR communities have been thoroughly studied, current understanding of the interactions between artificial and natural reefs (NRs) is poor and a fundamental question still to be answered is that of whether AR communities can mimic adjacent NR communities. We suggest three alternative hypotheses: Neighboring ARs and NRs will (1) achieve a similar community structure given sufficient time; (2) be similar only if they possess similar structural features; (3) always differ, regardless of age or structural features. We examined these hypotheses by comparing the community structure on a 119-year old shipwreck to a neighboring NR. Fouling organisms, including stony and soft corals, sponges, tunicates, sea anemones and hydrozoans were recorded and measured along belt transects. The ahermatypic stony coral Tubastrea micrantha dominated vertical AR regions while the soft corals Nephthea sp. and Xenia sp. dominated both artificial and natural horizontal surfaces. Our results support the second hypothesis, indicating that even after a century an AR will mimic its adjacent NR communities only if it possesses structural features similar to those of the natural surroundings. However, if the two differ structurally, their communities will remain distinct. PMID:16198411

  9. Nematode Community Structure in Forest Woodlots. II. Ordination of Nematode Communities.

    PubMed

    Johnson, S R; Ferris, J M; Ferris, V R

    1973-04-01

    Intersite relationships among nematode communities of 18 Indiana mixed hardwood stands of varying composition, soils, physiography and past management practices were determined by community ordination techniques. All sites were sampled in April, July and October of 1968 and 1969, and ordinations were based on the number of individuals of each nematode species at each site at each sampling period. The resulting groupings correlated well with groupings based on forest types and successional stages of the tree communities at the sites, and also with groupings based on well-defined soil types. Results were similar to those obtained previously with a resemblance equation which used qualitative data only; but the present study provided more information on species associations and relationships and ecological distance between sites. PMID:19319313

  10. Implications of nutrient removal and biomass production by native and augmented algal populations at a municipal wastewater treatment plant.

    PubMed

    Drexler, Ivy L C; Bekaan, Sascha; Eskandari, Yasmin; Yeh, Daniel H

    2014-01-01

    Algal monocultures (Chlorella sorokiniana and Botryococcus braunii) and algal communities native to clarifiers of a wastewater treatment plant were batch cultivated in (1) clarified effluent following a biochemical oxygen demand (BOD) removal reactor post-BOD removal clarified effluent (PBCE), (2) clarified effluent following a nitrification reactor post-nitrification clarified effluent (PNCE), and (3) a reference media (RM). After 12 days, all algal species achieved nitrogen removal between 68 and 82% in PBCE and 37 and 99% in PNCE, and phosphorus removal between 91 and 100% in PBCE and 60 and 100% in PNCE. The pH of the wastewater samples increased above 9.8 after cultivation of each species, which likely aided ammonia volatilization and phosphorus adsorption. Both monocultures grew readily with wastewater as a feedstock, but B. braunii experienced significant crowding from endemic fauna. In most cases, native algal species' nutrient removal efficiency was competitive with augmented algal monocultures, and in some cases achieved a higher biomass yield, demonstrating the potential to utilize native species for nutrient polishing and algal biomass production. PMID:25325538

  11. 40 CFR 797.1050 - Algal acute toxicity test.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ...) Algistatic means having the property of inhibiting algal growth. (3) ECx means the experimentally derived chemical concentration that is calculated to effect X percent of the test criterion. (4) Growth means a relative measure of the viability of an algal population based on the number and/or weight of algal...

  12. 40 CFR 797.1050 - Algal acute toxicity test.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ...) Algistatic means having the property of inhibiting algal growth. (3) ECx means the experimentally derived chemical concentration that is calculated to effect X percent of the test criterion. (4) Growth means a relative measure of the viability of an algal population based on the number and/or weight of algal...

  13. 40 CFR 797.1050 - Algal acute toxicity test.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ...) Algistatic means having the property of inhibiting algal growth. (3) ECx means the experimentally derived chemical concentration that is calculated to effect X percent of the test criterion. (4) Growth means a relative measure of the viability of an algal population based on the number and/or weight of algal...

  14. Impacts of Information Subsidies and Community Structure on Local Press Coverage of Environmental Contamination.

    ERIC Educational Resources Information Center

    Griffin, Robert J.; Dunwoody, Sharon

    1995-01-01

    Finds that a press kit sent by an environmental group to midwestern newspapers influenced them to delegate local staff to cover the story. Indicates that the press's function to report or raise issues concerning industrial toxic releases and related health risks is tempered by community structure and particularly by community reliance on…

  15. The Scope and Design of Structured Group Learning Experiences at Community Colleges

    ERIC Educational Resources Information Center

    Hatch, Deryl K.; Bohlig, E. Michael

    2015-01-01

    This study explores through descriptive analysis the similarities of structured group learning experiences such as first-year seminars, learning communities, orientation, success courses, and accelerated developmental education programs, in terms of their design features and implementation at community colleges. The study takes as its conceptual…

  16. The Impact of Differential Communication Structures on Rural Community Development Efforts.

    ERIC Educational Resources Information Center

    Voth, Donald E.; And Others

    1982-01-01

    Posits that increased communication of community leaders involving relatively short communications paths should lead to program success. However, measures of connectivity and average distance in the communications structure reveal no significant relationships. Suggests other factors which may be more important to rural community development…

  17. Soil microbial community structure and functionality during grassland restoration in the Texas High Plains

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil microbial communities are an indispensable part of restoration programs due to their significant role in ecosystem functioning and sensitivity to disturbance. We evaluated soil microbial community structure using ester-linked fatty acid (EL-FAME) profiling and metabolic functioning, by measurin...

  18. The fungal community structure of barley malts from diverse geographical regions correlates with malt quality parameters.

    PubMed

    Kaur, Mandeep; Bowman, John P; Stewart, Doug C; Evans, David E

    2015-12-23

    Malt is a preferred base for fermentations that produce beer or whisky. Barley for malt is grown under diverse environments in different geographical locations. Malt provides an ecological niche for a varied range of microorganisms with both positive and negative effects on its quality for brewing. Little information exists in the literature on the microbial community structure of Australian malt as well as broader global geographical differences in the associated fungal and bacterial communities. The aims of the present study were to compare the bacterial and fungal community structures of Australian commercial malt with its international counterparts originating from different geographical regions using terminal restriction fragment length polymorphism (TRFLP) fingerprinting and clone library analyses of ribosomal RNA genes. Further, the relationship between malt associated microbial communities and conventional malt quality parameters was also compared. Results showed that differences in fungal communities of malts from different geographical location were more pronounced than bacterial communities. TRFLP analysis discriminated high quality commercial malts with low fungal loads from malts deliberately infected with fungal inocula (Fusarium/Penicillium). Malt moisture, beta-amylase, α-amylase and limit dextrinase contents showed significant correlations with fungal community structure. This investigation concluded that fungal community structure was more important to subsequent malt quality outcomes than bacteria. PMID:26340674

  19. Structured decision making as a framework for linking quantitative decision support to community values

    EPA Science Inventory

    Community-level decisions can have large impacts on production and delivery of ecosystem services, which ultimately affects community well-being. But engaging stakeholders in a process to explore these impacts is a significant challenge. The principles of Structured Decision Ma...

  20. Creating Communities of Professionalism: Addressing Cultural and Structural Barriers

    ERIC Educational Resources Information Center

    Murphy, Joseph

    2015-01-01

    Purpose: The goal of this narrative synthesis is twofold. The purpose of this paper is to understand the barriers and constraints that hinder or prevent the growth of professional community. The author also want to form an empirical understanding of how educators can be successful in meeting these challenges. In both cases, the author wish to grow…

  1. Post fumigation recovery of soil microbial community structure

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil fumigants have been extensively used to control target soil-borne pathogens and weeds for the past few decades. It is known that the fumigants with broad biocidal activity can affect both target and non-target soil organisms, but the recovery of soil microbial communities are unknown until rece...

  2. Fungal and bacterial community structure downwind of a cattle feedyard

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soils provide a complex microhabitat for harboring a diverse group of microorganisms. The interaction of soil type, crop type, agroecosystem, and land management practices may all influence agricultural bacterial communities. In a previous study, we documented the long-term environmental impacts of ...

  3. Structure and composition of oligohaline marsh plant communities exposed to salinity pulses

    USGS Publications Warehouse

    Howard, R.J.; Mendelssohn, I.A.

    2000-01-01

    The response of two oligohaline marsh macrophyte communities to pulses of increased salinity was studied over a single growing season in a greenhouse experiment. The plant communities were allowed a recovery period in freshwater following the pulse events. The experimental treatments included: (1) salinity influx rate (rate of salinity increase from 0 to 12 gl-1); (2) duration of exposure to elevated salinity; and (3) water depth. The communities both included Sagittaria lancifolia L.; the codominant species were Eleocharis palustris (L.) Roemer and J.A. Schultes in community 1 and Schoenoplectus americanus (Pers.) Volk. ex Schinz and R. Keller in community 2. Effects of the treatments on sediment chemical characteristics (salinity, pH, redox potential, and sulfide and ammonium concentrations) and plant community attributes (aboveground and belowground biomass, stem density, leaf tissue nutrients, and species richness) were examined. The treatment effects often interacted to influence sediment and plant communities characteristics following recovery in fresh water. Salinity influx rate per se, however, had little effect on the abiotic or biotic response variables; significant influx effects were found when the 0 gl-1 (zero influx) treatment was compared to the 12 gl-1 treatments, regardless of the rate salinity was raised. A salinity level of 12 gl-1 had negative effects on plant community structure and composition; these effects were usually associated with 3 months of salinity exposure. Water depth often interacted with exposure duration, but increased water depth did independently decrease the values of some community response measures. Community 1 was affected more than community 2 in the most extreme salinity treatment (3 months exposure/15-cm water depth). Although species richness in both communities was reduced, structural changes were more dramatic in community 1. Biomass and stem density were reduced in community 1 overall and in both dominant species

  4. Genetic and environmental determinants of insect herbivore community structure in a Betula pendula population

    PubMed Central

    Silfver, Tarja

    2014-01-01

    A number of recent studies have shown that intraspecific genetic variation of plants may have a profound effect on the herbivorous communities which depend on them. However less is known about the relative importance of intraspecific variation compared to other ecological factors, for example environmental variation or the effects of herbivore damage. We randomly selected 22 Betula pendula genotypes from a local population (< 0.9 ha), cloned them and planted cloned seedlings on two study sites separated at a regional scale (distance between sites about 30 km) to examine an insect community of 23-27 species on these genotypes. B. pendula genotypes did not differ in their species richness, but the total mean abundance and the structure of the insect herbivore community was significantly affected by the genotype, which could account for up to 27% of the total variation in community structure. B. pendula genotype accounted for two to four times more variation in the arthropod community structure than did environmental (block) variation on a local scale, while on a regional scale, genotypic and environmental (site) variation accounted for 4-14% of the arthropod community structure. The genetic effects were modified by environmental variation on both a local and regional scale over one study year, and locally, the largest part of the variation (38%) could be explained by the genotype × environment (block) interactions. Suppression of insect herbivores during one growing season led to changed arthropod community structure in the following growing season, but this effect was minimal and could explain only 4% of the total variation in insect community structure. Our results suggest that both genetic and environmental factors are important determinants of the community structure of herbivorous insects. Together these mechanisms appear to maintain the high diversity of insects in B. pendula forest ecosystems. PMID:24715977

  5. Genetic and environmental determinants of insect herbivore community structure in a Betula pendula population.

    PubMed

    Silfver, Tarja; Rousi, Matti; Oksanen, Elina; Roininen, Heikki

    2014-01-01

    A number of recent studies have shown that intraspecific genetic variation of plants may have a profound effect on the herbivorous communities which depend on them. However less is known about the relative importance of intraspecific variation compared to other ecological factors, for example environmental variation or the effects of herbivore damage. We randomly selected 22 Betula pendula genotypes from a local population (< 0.9 ha), cloned them and planted cloned seedlings on two study sites separated at a regional scale (distance between sites about 30 km) to examine an insect community of 23-27 species on these genotypes. B. pendula genotypes did not differ in their species richness, but the total mean abundance and the structure of the insect herbivore community was significantly affected by the genotype, which could account for up to 27% of the total variation in community structure. B. pendula genotype accounted for two to four times more variation in the arthropod community structure than did environmental (block) variation on a local scale, while on a regional scale, genotypic and environmental (site) variation accounted for 4-14% of the arthropod community structure. The genetic effects were modified by environmental variation on both a local and regional scale over one study year, and locally, the largest part of the variation (38%) could be explained by the genotype × environment (block) interactions. Suppression of insect herbivores during one growing season led to changed arthropod community structure in the following growing season, but this effect was minimal and could explain only 4% of the total variation in insect community structure. Our results suggest that both genetic and environmental factors are important determinants of the community structure of herbivorous insects. Together these mechanisms appear to maintain the high diversity of insects in B. pendula forest ecosystems. PMID:24715977

  6. Effects of community structure on epidemic spread in an adaptive network.

    PubMed

    Tunc, Ilker; Shaw, Leah B

    2014-08-01

    When an epidemic spreads in a population, individuals may adaptively change the structure of their social contact network to reduce risk of infection. Here we study the spread of an epidemic on an adaptive network with community structure. We model two communities with different average degrees. The disease model is susceptible-infected-susceptible (SIS), and adaptation is rewiring of links between susceptibles and infectives. Locations of rewired links are selected so that the community structure will be preserved if susceptible-infective links are homogeneously distributed. The bifurcation structure is obtained, and a mean field model is developed that accurately predicts the steady-state behavior of the system. In a static network, weakly connected heterogeneous communities can have significantly different infection levels. In contrast, adaptation promotes similar infection levels and alters the network structure so that communities have more similar average degrees. We estimate the time for network restructuring to allow infection incursion from one community to another and show that it is inversely proportional to the number of cross-links between communities. In extremely heterogeneous systems, periodic oscillations in infection level can occur due to repeated infection incursions. PMID:25215775

  7. Fine-scale community and genetic structure are tightly linked in species-rich grasslands

    PubMed Central

    Whitlock, Raj; Bilton, Mark C.; Grime, J. Phil; Burke, Terry

    2011-01-01

    Recent evidence indicates that grassland community structure and species diversity are influenced by genetic variation within species. We review what is known regarding the impact of intraspecific diversity on grassland community structure, using an ancient limestone pasture as a focal example. Two genotype-dependent effects appear to modify community structure in this system. First, the abundance of individual constituent species can depend upon the combined influence of direct genetic effects stemming from individuals within the population. Second, the outcome of localized interspecific interactions occurring within the community can depend on the genotypes of participating individuals (indicating indirect genetic effects). Only genotypic interactions are thought to be capable of allowing the long-term coexistence of both genotypes and species. We discuss the implications of these effects for the maintenance of diversity in grasslands. Next, we present new observations indicating that losses of genotypic diversity from each of two species can be predicted by the abundance of other coexisting species within experimental grassland communities. These results suggest genotype-specific responses to abundance in other coexisting species. We conclude that both direct and indirect genetic effects are likely to shape community structure and species coexistence in grasslands, implying tight linkage between fine-scale genetic and community structure. PMID:21444309

  8. Effects of community structure on epidemic spread in an adaptive network

    NASA Astrophysics Data System (ADS)

    Tunc, Ilker; Shaw, Leah B.

    2014-08-01

    When an epidemic spreads in a population, individuals may adaptively change the structure of their social contact network to reduce risk of infection. Here we study the spread of an epidemic on an adaptive network with community structure. We model two communities with different average degrees. The disease model is susceptible-infected-susceptible (SIS), and adaptation is rewiring of links between susceptibles and infectives. Locations of rewired links are selected so that the community structure will be preserved if susceptible-infective links are homogeneously distributed. The bifurcation structure is obtained, and a mean field model is developed that accurately predicts the steady-state behavior of the system. In a static network, weakly connected heterogeneous communities can have significantly different infection levels. In contrast, adaptation promotes similar infection levels and alters the network structure so that communities have more similar average degrees. We estimate the time for network restructuring to allow infection incursion from one community to another and show that it is inversely proportional to the number of cross-links between communities. In extremely heterogeneous systems, periodic oscillations in infection level can occur due to repeated infection incursions.

  9. [Effects of Perfluoroalkyl Substances on the Microbial Community Structure in Surface Sediments of Typical River, China].

    PubMed

    Sun, Ya-jun; Wang, Tie-yu; Peng, Xia-wei; Wang, Pei

    2015-07-01

    In order to reveal the relationship between Perfluoroalkyl substances (PFASs) contamination and the bacterial community composition, surface sediment samples were collected along the Xiaoqing River in Shandong Province in April and July 2014 (XQ1-XQ10), where many PFASs manufacturers were located. PFASs were quantified by HPLC/MS-MS, related environmental factors affecting the microbial community structure were measured, and the microbial community structure in surface sediments was measured by the second-generation sequencing technology Illumina MiSeq. The results not only revealed the degree of PFASs pollution in the sediments of Xiaoqing River, but also illustrated the relationship between PFASs pollution and the microbial community structure. Among the twelve kinds of PFASs detected in this study, PFOA was the predominant compound, and the highest PFOA concentrations were detected in the sample of XQ5 (April: 456. 2 ng. g-1; July: 748.7 ng . g-1) located at the downstream of Xiaoqing River with many fluoropolymer producing facilities. PFOA contamination was the main factor affecting the microbial community structure in April, accordingly community richness and evenness were significantly negatively correlated with PFOA levels. The abundance of Thiobacillus increased with the increasing PFOA concentration in the sediment PFOA. This suggested that Thiobacillus was sensitive to PFOA pollution and might be the potential indicator to reveal the degree of PFOA pollution in sediment. When the concentrations of PFOA were below 100 ng . g-1, no significant effects on the microbial community structure were observed. PMID:26489317

  10. INSECT COMMUNITY STRUCTURE AS AN INDEX OF HEAVY-METAL POLLUTION IN LOTIC ECOSYSTEMS

    EPA Science Inventory

    Data from two stream suggest that macroinvertebrate community structure exhibits a predictable, graded response to heavy-metal pollution. In the more heavily stressed sections of both streams, macroinvertebrates, other than tubificid worms and chironomids, were virtually eliminat...

  11. ENVIRONMENTAL INFLUENCES ON BENTHIC COMMUNITY STRUCTURE IN A GREAT LAKES EMBAYMENT

    EPA Science Inventory

    An Intensified Environmental Monitoring and Assessment Program (EMAP) sampling grid in the St. Louis River estuary of western Lake Superior was used toassess the relationship between surficial sediment characteristics and benthic community structure. Ninety sites within two habit...

  12. TROPHIC STRUCTURE OF MACROBENTHIC COMMUNITIES IN NORTHERN GULF OF MEXICO ESTUARIES

    EPA Science Inventory

    Trophic structure of estuarine benthic communities in the northern Gulf of Mexico was characterized according to the functional roles and geographic distributions of the macrobenthos. acrobenthic organisms collected during two years of study were assigned to trophic groups to ass...

  13. Resolving Mixed Algal Species in Hyperspectral Images

    PubMed Central

    Mehrubeoglu, Mehrube; Teng, Ming Y.; Zimba, Paul V.

    2014-01-01

    We investigated a lab-based hyperspectral imaging system's response from pure (single) and mixed (two) algal cultures containing known algae types and volumetric combinations to characterize the system's performance. The spectral response to volumetric changes in single and combinations of algal mixtures with known ratios were tested. Constrained linear spectral unmixing was applied to extract the algal content of the mixtures based on abundances that produced the lowest root mean square error. Percent prediction error was computed as the difference between actual percent volumetric content and abundances at minimum RMS error. Best prediction errors were computed as 0.4%, 0.4% and 6.3% for the mixed spectra from three independent experiments. The worst prediction errors were found as 5.6%, 5.4% and 13.4% for the same order of experiments. Additionally, Beer-Lambert's law was utilized to relate transmittance to different volumes of pure algal suspensions demonstrating linear logarithmic trends for optical property measurements. PMID:24451451

  14. AL HARMFUL ALGAL BLOOM (HAB) INFORMATION EXCHANGE

    EPA Science Inventory

    This project proposes to implement an integrated web site that will serve as an Alabama Harmful Algal Bloom (HAB) Information Exchange Network. This network will be a stand-alone site where HAB data from all agencies and research efforts in the State of Alabama will be integrate...

  15. Using hyperspectral imagery to monitor algal persence

    SciTech Connect

    Anderson, J.M.; Monk, J.; Yan, Gu; Brignal, W.

    1997-08-01

    This paper illustrates how an inexpensive and easily deployable imaging spectrometer can be used to monitor and identify algal blooms at short notice, thus making practical the addition of airborne data to the usual in-situ measurements. Two examples are described, one in the Irish Sea and the other in a reservoir system in the London area.

  16. Algal production in wastewater treatment high rate algal ponds for potential biofuel use.

    PubMed

    Park, J B K; Craggs, R J

    2011-01-01

    Wastewater treatment High Rate Algal Ponds with CO2 addition could provide cost-effective and efficient tertiary-level wastewater treatment with the co-benefit of algal biomass production for biofuel use. Wastewater grown algal biomass can have a lipid content of 10-30% of dry weight, which could be used to make biodiesel. This research investigated algal biomass and total lipid production by two pilot-scale wastewater treatment HRAP(S) (4-day HRT) with and without CO2 addition under New Zealand mid summer (Nov-Jan) conditions. The influence of CO2 addition on wastewater treatment performance was also determined. CO2 was added to one of the HRAPs (the HRAP(E)) by maintaining the maximum pH of the pond below 8. Measurements of HRAP influent and effluent water qualities, total lipid content and algal biomass production were made twice a week over the experimental period. Both HRAP(S) achieved high levels of organic compound and nutrient removal, with >85% SBOD5, >92 NH4(+)-N and >70% DRP removal. Algal/bacterial biomass production in the HRAP(E) (15.2 g/m2/d) was improved by CO2 addition by approximately 30% compared with that of the control HRAP(W) (10.6 g/m2/d). Total lipid content of the biomass grown on both HRAP(S) was slightly reduced (from 25% to 20%) with CO2 addition and the maximum total lipid content of approximately 40% was observed in the HRAP(W) when low NH4(+)-N concentration (<0.5 mg/L) and high maximum pH (>10.0) occurred. Total lipid content of the biomass increased by approximately 15% under nitrogen limiting conditions, however, overall algal/bacterial biomass production was reduced by half during the period of nitrogen limitation. More research is required to maintain algal production under near nitrogen-limiting conditions. PMID:21977667

  17. Developing Structured-Learning Exercises for a Community Advanced Pharmacy Practice Experience

    PubMed Central

    Thomas, Renee Ahrens

    2006-01-01

    The recent growth in the number of pharmacy schools across the nation has resulted in the need for high-quality community advanced pharmacy practice experience (APPE) sites. A vital part of a student's education, these APPEs should be structured and formalized to provide an environment conducive to student learning. This paper discusses how to use a calendar, structured-learning activities, and scheduled evaluations to develop students' knowledge, skills, and abilities in a community pharmacy setting. PMID:17136164

  18. Wave action modifies the effects of consumer diversity and warming on algal assemblages.

    PubMed

    Mrowicki, Robert J; O'Connor, Nessa E

    2015-04-01

    To understand the consequences of biodiversity loss, it is necessary to test how biodiversity-ecosystem functioning relationships may vary with predicted environmental change. In particular, our understanding will be advanced by studies addressing the interactive effects of multiple stressors on the role of biodiversity across trophic levels. Predicted increases in wave disturbance and ocean warming, together with climate-driven range shifts of key consumer species, are likely to have profound impacts on the dynamics of coastal marine communities. We tested whether wave action and temperature modified the effects of gastropod grazer diversity (Patella vulgata, Littorina littorea, and Gibbula umbilicalis) on algal assemblages in experimental rock pools. The presence or absence of L. littorea appeared to drive changes in microalgal and macroalgal biomass and macroalgal assemblage structure. Macroalgal biomass also decreased with increasing grazer species richness, but only when wave action was enhanced. Further, independently of grazer diversity, wave action and temperature had interactive effects on macroalgal assemblage structure. Warming also led to a reversal of grazer-macroalgal interaction strengths from negative to positive, but only when there was no wave action. Our results show that hydrodynamic disturbance can exacerbate the effects of changing consumer diversity, and may also disrupt the influence of other environmental stressors on key consumer-resource interactions. These findings suggest that the combined effects of anticipated abiotic and biotic change on the functioning of coastal marine ecosystems, although difficult to predict, may be substantial. PMID:26230022

  19. Activity and structure of methanotrophic communities in landfill cover soils.

    PubMed

    Gebert, Julia; Singh, Brajesh Kumar; Pan, Yao; Bodrossy, Levente

    2009-10-01

    The composition of the methanotrophic community in soil covers on five landfills in Northern and Eastern Germany was investigated by means of diagnostic microarray and terminal restriction fragment length polymorphism (T-RFLP), both targeting the pmoA gene of methanotrophs. Physical and chemical properties of the 15 sampled soil profiles varied greatly, thus providing for very different environmental conditions. The potential methane oxidation activity, assessed using undisturbed soil cores, varied between 0.2 and 28 µg CH4 gdw (-1)  h(-1) , the latter amounting to 426 g CH4 m(-2)  h(-1) . Total nitrogen was found to be the soil variable correlating most strongly with methanotrophic activity. Explaining close to 50% of the observed variability, this indicates that on the investigated sites activity and thus abundance of methanotrophs may have been nitrogen-limited. Variables that enhance organic matter and thus nitrogen accumulation, such as field capacity, also positively impacted methanotrophic activity. In spite of the great variability of soil properties and different geographic landfill location, both microarray and T-RFLP analysis suggested that the composition of the methanotrophic community on all five sites, in all profiles and across all depths was similar. Methylocystis, Methylobacter and Methylococcus species, including Methylococcus-related uncultivated methanotrophs, were predominantly detected among type II, Ia and Ib methanotrophs, respectively. This indicates that the high methane fluxes typical for landfill environments may be the most influential driver governing the community composition, or other variables not analysed in this study. Principal component analysis suggested that community diversity is most influenced by the site from which the samples were taken and second, from the location on the individual sites, i.e. the soil profile. Landfill and individual profiles reflect the combined impact of all effective variables, including

  20. From MERIS To OLCI And Sentinel 2: Harmful Algal Bloom Applications & Modelling In South Africa

    NASA Astrophysics Data System (ADS)

    Robertson Lain, L.; Bernard, S.; Evers-King, H.; Matthews, M. W.; Smith, M.

    2013-12-01

    The Sentinel 2 and 3 missions offer new capabilities for Harmful Algal Bloom (HAB) observations in Southern Africa and further afield on the African continent where there is a great need for improved monitoring of water quality: both in freshwater resources where eutrophication is common, and in vulnerable coastal ecosystems. Two well validated algorithms - Equivalent Algal Populations (EAP) & Maximum Peak Height (MPH) - available for operational use on eutrophic waters are described. Spectral remote sensing reflectances (Rrs) and inherent optical properties (IOPs) are characterised via measurement and modelling of phytoplankton assemblages typical of high biomass algal blooms of the Southern Benguela and inland waters of South Africa. Sensitivity to phytoplankton functional types (PFTs) is investigated, with focus on optically significant biological characteristics e.g. particle size distribution and intracellular structure (including vacuoles).

  1. [Structural characteristics of Hemiptelea davidii community on Kerqin sandy land].

    PubMed

    Bai, Yun-Peng; Han, Da-Yong; Dong, Yan-Hong; Zhao, Yu-Jing; Li, Jian-Dong

    2008-02-01

    An investigation was made on the species composition and eco-type of Hemiptelea davidii community on Kerqin sandy land. The results showed that in study area, no shrub layer existed in H. davidii forest, while arbor layer could be divided into two sub-layers, with a height of 4.05-7.86 m for the upper layer, and of 2.05-3.20 m for the lower layer. In the community, there were 32 herbal species belonging to 27 genera of 13 families and dominant by Poaceae, Fabaceae and Compositae, and 11 areal types, among which, the species number in Mongolian-Northeastern China-Dahuricia-North China areal type was the highest (34.38%), followed by that in Northeastern China-North China areal type (12.5%). Among three water ecological types, mesophytes occupied 59.37% of the total, and mesoxerophytes and xerophytes occupied 25% and 15.63%, respectively. Hemicryptophytes had a larger amount in six life forms, accounting for 31.25% of the total. H. davidii community had the typical life form characteristics of temperate steppe. PMID:18464628

  2. Bacterial community structure is indicative of chemical inputs in the Upper Mississippi River

    PubMed Central

    Staley, Christopher; Gould, Trevor J.; Wang, Ping; Phillips, Jane; Cotner, James B.; Sadowsky, Michael J.

    2014-01-01

    Local and regional associations between bacterial communities and nutrient and chemical concentrations were assessed in the Upper Mississippi River in Minnesota to determine if community structure was associated with discrete types of chemical inputs associated with different land cover. Bacterial communities were characterized by Illumina sequencing of the V6 region of 16S rDNA and compared to >40 chemical and nutrient concentrations. Local bacterial community structure was shaped primarily by associations among bacterial orders. However, order abundances were correlated regionally with nutrient and chemical concentrations, and were also related to major land coverage types. Total organic carbon and total dissolved solids were among the primary abiotic factors associated with local community composition and co-varied with land cover. Escherichia coli concentration was poorly related to community composition or nutrient concentrations. Abundances of 14 bacterial orders were related to land coverage type, and seven showed significant differences in abundance (P ≤ 0.046) between forested or anthropogenically-impacted sites. This study identifies specific bacterial orders that were associated with chemicals and nutrients derived from specific land cover types and may be useful in assessing water quality. Results of this study reveal the need to investigate community dynamics at both the local and regional scales and to identify shifts in taxonomic community structure that may be useful in determining sources of pollution in the Upper Mississippi River. PMID:25339945

  3. Bacterial community structure and soil properties of a subarctic tundra soil in Council, Alaska

    PubMed Central

    Kim, Hye Min; Jung, Ji Young; Yergeau, Etienne; Hwang, Chung Yeon; Hinzman, Larry; Nam, Sungjin; Hong, Soon Gyu; Kim, Ok-Sun; Chun, Jongsik; Lee, Yoo Kyung

    2014-01-01

    The subarctic region is highly responsive and vulnerable to climate change. Understanding the structure of subarctic soil microbial communities is essential for predicting the response of the subarctic soil environment to climate change. To determine the composition of the bacterial community and its relationship with soil properties, we investigated the bacterial community structure and properties of surface soil from the moist acidic tussock tundra in Council, Alaska. We collected 70 soil samples with 25-m intervals between sampling points from 0–10 cm to 10–20 cm depths. The bacterial community was analyzed by pyrosequencing of 16S rRNA genes, and the following soil properties were analyzed: soil moisture content (MC), pH, total carbon (TC), total nitrogen (TN), and inorganic nitrogen ( and ). The community compositions of the two different depths showed that Alphaproteobacteria decreased with soil depth. Among the soil properties measured, soil pH was the most significant factor correlating with bacterial community in both upper and lower-layer soils. Bacterial community similarity based on jackknifed unweighted unifrac distance showed greater similarity across horizontal layers than through the vertical depth. This study showed that soil depth and pH were the most important soil properties determining bacterial community structure of the subarctic tundra soil in Council, Alaska. PMID:24893754

  4. The green macroalga Dictyosphaeria ocellata influences the structure of the bacterioplankton community through differential effects on individual bacterial phylotypes.

    PubMed

    Sneed, Jennifer M; Pohnert, Georg

    2011-02-01

    Marine macroalgae are subjected to large numbers of bacteria in their environment. These bacteria have the potential to affect the health and ecology of algae in a variety of ways and can be both beneficial and harmful to the algae. Therefore, algae have likely evolved mechanisms to differentially regulate the growth of bacterial species. In this study, we examined the effects of the green alga Dictyosphaeria ocellata on the bacterioplankton community in field enclosure experiments and on individual, naturally co-occurring bacterial strains in laboratory co-culture experiments. In field experiments, we compared the bacterioplankton communities of enclosures with and without D. ocellata using denaturing gradient gel electrophoresis and found that the alga significantly changed the bacterial community composition. Seven bacterial phylotypes were eliminated in the presence of the alga and five were found exclusively with the alga. We also examined the effects of algal-treated water on the development of the bacterial community within enclosures and found no change in the community composition. Laboratory co-culture experiments revealed that D. ocellata and D. ocellata extracts affect the growth of individual bacterial strains in a species-specific manner and that the mechanisms responsible for these effects also differed by bacterial species. PMID:21155850

  5. Algal toxins alter copepod feeding behavior.

    PubMed

    Hong, Jiarong; Talapatra, Siddharth; Katz, Joseph; Tester, Patricia A; Waggett, Rebecca J; Place, Allen R

    2012-01-01

    Using digital holographic cinematography, we quantify and compare the feeding behavior of free-swimming copepods, Acartia tonsa, on nutritional prey (Storeatula major) to that occurring during exposure to toxic and non-toxic strains of Karenia brevis and Karlodinium veneficum. These two harmful algal species produce polyketide toxins with different modes of action and potency. We distinguish between two different beating modes of the copepod's feeding appendages-a "sampling beating" that has short durations (<100 ms) and involves little fluid entrainment and a longer duration "grazing beating" that persists up to 1200 ms and generates feeding currents. The durations of both beating modes have log-normal distributions. Without prey, A. tonsa only samples the environment at low frequency. Upon introduction of non-toxic food, it increases its sampling time moderately and the grazing period substantially. On mono algal diets for either of the toxic dinoflagellates, sampling time fraction is high but the grazing is very limited. A. tonsa demonstrates aversion to both toxic algal species. In mixtures of S. major and the neurotoxin producing K. brevis, sampling and grazing diminish rapidly, presumably due to neurological effects of consuming brevetoxins while trying to feed on S. major. In contrast, on mixtures of cytotoxin producing K. veneficum, both behavioral modes persist, indicating that intake of karlotoxins does not immediately inhibit the copepod's grazing behavior. These findings add critical insight into how these algal toxins may influence the copepod's feeding behavior, and suggest how some harmful algal species may alter top-down control exerted by grazers like copepods. PMID:22629336

  6. [The ethiology structure of community-acquried pneumonia of young adults in closed communities].

    PubMed

    Nosach, E S; Skryl', S V; Kulakova, N V; Martynova, A V

    2012-01-01

    Despite of success in ethiology evaluation of community-acquired pneumonia (CAP) and instant improvement of diagnostic methods microbiological spectrum of CAP is still remaining underestimated and is still the problem for the routine clinical practice. In our study we estimated the role of fastidious bacteria which cause atypical CAP such as Chlamydophilla pneumoniae, Mycoplasma pneumoniae, Legionella pneumophila. Furthermore we also defined the role of viral pathogens in ethiology of CAP. PMID:23013002

  7. Microbial communities of urban stormwater sediments: the phylogenetic structure of bacterial communities varies with porosity.

    PubMed

    Badin, Anne-Laure; Mustafa, Tarfa; Bertrand, Cédric; Monier, Armelle; Delolme, Cécile; Geremia, Roberto A; Bedell, Jean-Philippe

    2012-08-01

    This study focuses on the distribution of bacterial and fungal communities within the microstructure of a multi-contaminated sedimentary layer resulting from urban stormwater infiltration. Fractionation was performed on the basis of differential porosity and aggregate grain size, resulting in five fractions: leachable fitting macroporosity, < 10, 10-160, 160-1000 μm fitting aggregates, > 1000 μm. Amounts of both bacterial and fungal biomasses are greater in the < 10 μm and leachable fractions. The aggregates contain numerous bacteria but very low amounts of fungal biomass. Single-strand conformational polymorphism molecular profiles highlighted the differences between bacterial and fungal communities of the leachable fraction and those of the aggregates. Random Sanger sequencing of ssu clones revealed that these differences were mainly because of the presence of Epsilonproteobacteria and Firmicutes in the leachable fractions, while the aggregates contained more Cyanobacteria. The Cyanobacteria phylotypes in the aggregates were dominated by the sequences related to Microcoleus vaginatus while the leachable fractions presented the sequences of chloroplastic origin. Therefore, more than 50% of the phylotypes observed were related to Proteobacteria while 40% were related to Cyanobacteria and Bacteroidetes. Preferential distribution of clades in almost all the phyla or classes detected was observed. This study provides insight into the identities of dominant members of the bacterial communities of urban sediments. Microcoleus vaginatus appeared to predominate in pioneer soils. PMID:22404135

  8. Algal refossilization of atmospheric carbon dioxide. [Contains bibliography

    SciTech Connect

    Neushul, M. )

    1991-07-01

    The atmospheric concentration of carbon dioxide (CO{sub 2}) is steadily increasing. With our increasing awareness of the economic and environmental impacts of the greenhouse effects'' of CO{sub 2}, methane and other gases, there is interest in finding new methods to reduce the amounts of these gases in the atmosphere. This study evaluates the possibility that large-scale oceanic cultures of macroalgae (macroscopic seaweeds'') could be used to capture atmospheric CO{sub 2}. It is a design for a marine farm system in which a crop'' of calcareous macroalgae grows attached to, and supported by, floating macroalgae that comprise the farm structure.'' The least complicated, yet feasible, macroalgal farm system appears to be one in which laboratory-propagated calcareous algal epiphytes'' and floating algal basiphytes'' are dispersed together in natural ocean upwelling regions. From there, the plants drift with surface currents to the open ocean and then sink to the sea floor, where the buried carbon is refossilized.'' An important caveat regarding the use of calcareous algae is that the process of calcification may release CO{sub 2} to the atmosphere. There is some evidence that CO{sub 2} is not released by calcification in red calcareous algae, but in contrast many geochemists feel that all biologically -- as well as chemically --mediated calcification processes release CO{sub 2}. A substantial amount of research will be necessary to answer basic questions about algal carbon fixation and biomineralization on one hand, while on the other hand to devise strategies for farming the open ocean. 76 refs., 14 figs., 7 tabs.

  9. Biological Soil Crusts from Coastal Dunes at the Baltic Sea: Cyanobacterial and Algal Biodiversity and Related Soil Properties.

    PubMed

    Schulz, Karoline; Mikhailyuk, Tatiana; Dreßler, Mirko; Leinweber, Peter; Karsten, Ulf

    2016-01-01

    Biological soil crusts (BSCs) are known as "ecosystem-engineers" that have important, multifunctional ecological roles in primary production, in nutrient and hydrological cycles, and in stabilization of soils. These communities, however, are almost unstudied in coastal dunes of the temperate zone. Hence, for the first time, the biodiversity of cyanobacterial and algal dominated BSCs collected in five dunes from the southern Baltic Sea coast on the islands Rügen and Usedom (Germany) was investigated in connection with physicochemical soil parameters. The species composition of cyanobacteria and algae was identified with direct determination of crust subsamples, cultural methods, and diatom slides. To investigate the influence of soil properties on species composition, the texture, pH, electrical conductivity, carbonate content, total contents of carbon, nitrogen, phosphorus, and the bioavailable phosphorus-fraction (PO4 (3-)) were analyzed in adjacent BSC-free surface soils at each study site. The data indicate that BSCs in coastal dunes of the southern Baltic Sea represent an ecologically important vegetation form with a surprisingly high site-specific diversity of 19 cyanobacteria, 51 non-diatom algae, and 55 diatoms. All dominant species of the genera Coleofasciculus, Lyngbya, Microcoleus, Nostoc, Hydrocoryne, Leptolyngbya, Klebsormidium, and Lobochlamys are typical aero-terrestrial cyanobacteria and algae, respectively. This first study of coastal sand dunes in the Baltic region provides compelling evidence that here the BSCs were dominated by cyanobacteria, algae, or a mixture of both. Among the physicochemical soil properties, the total phosphorus content of the BSC-free sand was the only factor that significantly influenced the cyanobacterial and algal community structure of BSCs in coastal dunes. PMID:26507846

  10. Stream invertebrate communities of Mongolia: current structure and expected changes due to climate change

    PubMed Central

    2012-01-01

    Background Mongolia’s riverine landscape is divided into three watersheds, differing in extent of permafrost, amount of precipitation and in hydrological connectivity between sub-drainages. In order to assess the vulnerability of macroinvertebrate communities to ongoing climate change, we consider the taxonomic and functional structures of stream communities in two major watersheds: The Central Asian Internal Watershed (CAIW) and the Arctic Ocean Watershed (AOW), together covering 86.1% of Mongolia’s surface area. We assess the consequences of the hydrological connectivity between sub-drainages on the nestedness and distinctness of the stream communities. And accordingly, we discuss the expected biotic changes to occur in each watershed as a consequence of climate change. Results Gamma and beta diversities were higher in the CAIW than the AOW. High community nestedness was also found in the CAIW along with a higher heterogeneity of macroinvertebrate assemblage structure. Assemblages characteristic of cold headwater streams in the CAIW, were typical of the drainages of the Altai Mountain range. Macroinvertebrate guilds of the CAIW streams exhibited traits reflecting a high stability and low resilience capacity for eutrophication. In contrast, the community of the AOW had lower nestedness and a combination of traits reflecting higher stability and a better resilience capacity to disturbances. Conclusion Higher distinctness of stream communities is due to lower connectivity between the drainages. This was the case of the stream macroinvertebrate communities of the two major Mongolian watersheds, where connectivity of streams between sub-drainages is an important element structuring their communities. Considering differences in the communities’ guild structure, hydrological connectivity and different magnitudes of upcoming impacts of climate change between the two watersheds, respective stream communities will be affected differently. The hitherto different

  11. The spatial arrangement of reefs alters the ecological patterns of fauna between interspersed algal habitats

    NASA Astrophysics Data System (ADS)

    Tuya, F.; Wernberg, T.; Thomsen, M. S.

    2008-07-01

    Reef landscapes dominated by canopy-forming species are often irregular mosaics of habitats, with important influences on associated fauna. This study tested if differences in the ecological patterns of mobile fauna inhabiting interspersed (morphologically distinct) algal habitats were altered by the spatial arrangement of reefs of varying proximity to the shoreline. Specifically, prosobranch gastropods were used as models to test that: (1) there were differences in the ecological patterns (species composition and abundances) between three algal habitats (the kelp Ecklonia radiata, fucalean macroalgae, and erect red algae); (2) the magnitude of these differences depended on the position of reef lines ('in-shore' vs. 'off-shore'); and (3) these effects were regionally consistent across a ˜4° latitudinal gradient (˜600 km of coastline) in Western Australia. The ecological patterns of algal-associated gastropods responded strongly to the presence of algal habitats with different physical structure at small spatial scales. Importantly, differences in assemblage structure (e.g. differences in total abundances) between habitats across the latitudinal gradient were especially accentuated on the in-shore reefs compared with the off-shore reefs, where a general amelioration of differences between habitats was observed, probably associated with a more widespread effect of stronger wave forces across habitats. Overall, red algae supported higher total abundances and species richness (per algal weight) compared to the other algal habitats, particularly on in-shore reefs. Patterns for individual species were considerably location-dependent, reflecting the natural variability of species across geographical gradients. In contrast, patterns at the assemblage-level were consistent, providing evidence for the existence of general rules underlying the assemblage-level organization of mobile invertebrates on subtidal reefs across this geographical gradient.

  12. Formation of iron-rich shelled structures by microbial communities

    NASA Astrophysics Data System (ADS)

    Fernández-Remolar, David C.; Santamaría, Joan; Amils, Ricardo; Parro, Victor; Gómez-Ortíz, D.; Izawa, Matthew R. M.; Banerjee, Neil R.; Pérez Rodríguez, Raúl; Rodríguez, Nuria; López-Martínez, Nieves

    2015-01-01

    this paper, we describe the discovery and characterization of shelled structures that occur inside galleries of Pyrenees mines. The structures are formed by the mineralization of iron and zinc oxides, dominantly franklinite (ZnFe2O4) and poorly ordered goethite (α-FeO(OH)). Subsurface oxidation and hydration of polymetallic sulfide orebodies produce solutions rich in dissolved metal cations including Fe2+/3+ and Zn2+. The microbially precipitated shell-like structure grows by lateral or vertical stacking of thin laminae of iron oxide particles which are accreted mostly by fungal filaments. The resulting structures are composed of randomly oriented aggregates of needle-like, uniform-sized crystals, suggesting some biological control in the structure formation. Such structures are formed by the integration of two separated shells, following a complex process driven likely by different strategies of fungal microorganisms that produced the complex macrostructure.

  13. Structures of Microbial Communities in Alpine Soils: Seasonal and Elevational Effects

    PubMed Central

    Lazzaro, Anna; Hilfiker, Daniela; Zeyer, Josef

    2015-01-01

    Microbial communities in alpine environments are exposed to several environmental factors related to elevation and local site conditions and to extreme seasonal variations. However, little is known on the combined impact of such factors on microbial community structure. We assessed the effects of seasonal variations on soil fungal and bacterial communities along an elevational gradient (from alpine meadows to a glacier forefield, 1930–2519 m a.s.l.) over 14 months. Samples were taken during all four seasons, even under the winter snowpack and at snowmelt. Microbial community structures and abundances were investigated using Terminal Restriction Fragment Length Polymorphism (T-RFLP) and quantitative PCR (qPCR) of the 16S and 18S rRNA genes. Illumina sequencing was performed to identify key bacterial groups in selected samples. We found that the soil properties varied significantly with the seasons and along the elevational gradient. For example, concentrations of soluble nutrients (e.g., NH4+-N, SO42−-S, PO43−-P) significantly increased in October but decreased drastically under the winter snowpack. At all times, the alpine meadows showed higher soluble nutrient concentrations than the glacier forefield. Microbial community structures at the different sites were strongly affected by seasonal variations. Under winter snowpack, bacterial communities were dominated by ubiquitous groups (i.e., beta-Proteobacteria, which made up to 25.7% of the total reads in the glacier forefield). In the snow-free seasons, other groups (i.e., Cyanobacteria) became more abundant (from 1% under winter snow in the glacier forefield samples to 8.1% in summer). In summary, elevation had a significant effect on soil properties, whereas season influenced soil properties as well as microbial community structure. Vegetation had a minor impact on microbial communities. At every elevation analyzed, bacterial, and fungal community structures exhibited a pronounced annual cycle. PMID:26635785

  14. The Topological Characteristics and Community Structure in Consumer-Service Bipartite Graph

    NASA Astrophysics Data System (ADS)

    Li, Lin; Gu, Bao-Yan; Chen, Li

    We apply network analysis to study bipartite consumer- service graph that represents service transaction to understand consumer demand. Based on real-world computer log files of a library, we found that consumer graph projected from bipartite graph deviates significantly from theoretical predictions based on random bipartite graph. We observed smaller-than-expected average degree, larger-than-expected average path length and stronger-than-expected tendency to cluster. These findings motivated to explore the community structure of the network. As a result, the weighted consumer network showed significant community structure than the unweighted network. Communities picked out by the algorithm revealed that individuals in the same community were due to their common specialties or the overlapping structure of knowledge between their specialties.

  15. Community structure and scale-free collections of Erdős-Rényi graphs.

    PubMed

    Seshadhri, C; Kolda, Tamara G; Pinar, Ali

    2012-05-01

    Community structure plays a significant role in the analysis of social networks and similar graphs, yet this structure is little understood and not well captured by most models. We formally define a community to be a subgraph that is internally highly connected and has no deeper substructure. We use tools of combinatorics to show that any such community must contain a dense Erdős-Rényi (ER) subgraph. Based on mathematical arguments, we hypothesize that any graph with a heavy-tailed degree distribution and community structure must contain a scale-free collection of dense ER subgraphs. These theoretical observations corroborate well with empirical evidence. From this, we propose the Block Two-Level Erdős-Rényi (BTER) model, and demonstrate that it accurately captures the observable properties of many real-world social networks. PMID:23004823

  16. Structure and seasonality in a Malaysian mudflat community

    NASA Astrophysics Data System (ADS)

    Broom, M. J.

    1982-08-01

    An assessment of community composition and the functional roles of the dominant species has been carried out in two intertidal areas of Malaysian mudflat dominated by natural populations of the arcid bivalve mollusc Anadara granosa. In addition to A. granosa, organisms of numerical importance are the venerid bivalve Pelecyora trigona, the neogastropod Plicarcularia leptospira, the mesogastropods Stenothyra glabrata and Cerithidea cingulata and the hermit crab Diogenes sp. The mesogastropod Natica maculosa and the neogastropod Thais carinifera may be of some importance to community organization but they are not numerically dominant. Annelids are conspicuous by their absence. The following trophic roles are ascribed to specific members of the community: A. granosa—facultative surface deposit feeder; P. trigona—suspension feeder; P. leptospira—scavenger; C. cingulata—deposit feeder/grazer; S. glabrata—deposit feeder/grazer; N. maculosa—predator; T. carinifera—predator; Diogenes sp.—scavenger/predator. S. glabrata is of particular interest because it appears to fill the niche occupied by mud snails of the genus Hydrobia in temperate mudflat systems. There is evidence of seasonality on the mudflats which points to a spawning of certain forms triggered by the major annual salinity depression at the time of the onset of the north-east monsoon in October/November. Concentrations of benthic chlorophyll a show no obvious signs of a seasonal fluctuation and the seasonality of the primary consumers is not thought to be related to food abundance. However there is some evidence of seasonality of reproduction in N. maculosa which preys on the seasonally reproducing bivalves.

  17. Effects of changing continuous iron input rates on a Southern Ocean algal assemblage

    NASA Astrophysics Data System (ADS)

    Hare, C. E.; DiTullio, G. R.; Riseman, S. F.; Crossley, A. C.; Popels, L. C.; Sedwick, P. N.; Hutchins, D. A.

    2007-05-01

    The upwelling of nutrients and iron (Fe) sustains biological production in much of the Southern Ocean. Using a shipboard natural community continuous culture system (Ecostat), we supplied a single added Fe concentration at two dilution rates chosen to examine the effects of variations in realistic growth and loss rates on an Fe-limited algal community in the Antarctic Zone south of Australia. A parallel growout experiment provided "no-dilution" +Fe and -Fe controls. In the continuous flow experiment, phytoplankton biomass was lower and more constant throughout the incubation and major nutrients were never depleted. Nanophytoplankton abundance remained similar in both growout treatments, and therefore, growth of this group did not appear to be Fe-limited. The addition of Fe in a continuous fashion resulted in a community co-dominated by both small diatoms and nanophytoplankton. Increases in dilution rate favored diatom species that were smaller and faster-growing, as well as non-silicified algal groups. Particulate carbon (PC) to particulate nitrogen (PN) ratios increased above the Redfield ratio when Fe was added in a continuous fashion, while biogenic silica (BSi) to PC and PN ratios decreased 2-3 fold in the continuous flow experiment compared to the initial conditions and the parallel growout control experiment. Photosynthetic efficiency increased in the continuous flow treatments above the control but remained significantly lower than in the 1.4 nM Fe addition. The results of our shipboard continuous flow experiments are compared and contrasted with those of the mesoscale Southern Ocean Iron RElease Experiment (SOIREE) carried out at the same site. Our results suggest that increases in natural dilution rates (i.e. vertical turbulent diffusion) in polar Antarctic waters could shift the algal community towards smaller, faster-growing algal species, thus having a major effect on nutrient cycling and carbon export in the Southern Ocean.

  18. Cyanobacterial Community Structure In Lithifying Mats of A Yellowstone Hotspring-Implications for Precambrian Stromatolite Biocomplexity

    NASA Technical Reports Server (NTRS)

    Lau, Evan; Nash, C. Z.; Vogler, D. R.; Cullings, K.; DeVincenzi, Donald (Technical Monitor)

    2002-01-01

    Denaturing Gradient Gel Electrophoresis (DGGE) of partial 16S rRNA gene sequences was used to investigate the molecular biodiversity of cyanobacterial communities inhabiting various lithified morpho-structures in two hotsprings of Yellowstone National Park. These morpho-structures - flat-topped columns, columnar cones, and ridged cones - resemble ancient stromatolites, which are possibly biogenic in origin. The top, middle and bottom sections of these lithified morpho-structures, as well as surrounding non-lithified mats were analyzed to determine the vertical and spatial distribution of cyanobacterial communities. Results from DGGE indicate that the cyanobacterial community composition of lithified morpho-structures (flat-topped columns, columnar cones, and ridged cones) were largely similar in vertical distribution as well as among the morpho-structures being studied. Preliminary results indicate that the cyanobacterial communities in these lithified morpho-structures were significantly different from communities in surrounding non-lithified mats. These results provide additional support to the theory that certain Phormidium/Leptolyngbya species are involved in the morphogenesis of lithifying morpho-structures in hotsprings and may have played a role in the formation of ancient stromatolites.

  19. Direct and Indirect Influence of Parental Bedrock on Streambed Microbial Community Structure in Forested Streams▿

    PubMed Central

    Mosher, Jennifer J.; Findlay, Robert H.

    2011-01-01

    A correlative study was performed to determine if variation in streambed microbial community structure in low-order forested streams can be directly or indirectly linked to the chemical nature of the parental bedrock of the environments through which the streams flow. Total microbial and photosynthetic biomass (phospholipid phosphate [PLP] and chlorophyll a), community structure (phospholipid fatty acid analysis), and physical and chemical parameters were measured in six streams, three located in sandstone and three in limestone regions of the Bankhead National Forest in northern Alabama. Although stream water flowing through the two different bedrock types differed significantly in chemical composition, there were no significant differences in total microbial and photosynthetic biomass in the sediments. In contrast, sedimentary microbial community structure differed between the bedrock types and was significantly correlated with stream water ion concentrations. A pattern of seasonal variation in microbial community structure was also observed. Further statistical analysis indicated dissolved organic matter (DOM) quality, which was previously shown to be influenced by geological variation, correlated with variation in bacterial community structure. These results indicate that the geology of underlying bedrock influences benthic microbial communities directly via changes in water chemistry and also indirectly via stream water DOM quality. PMID:21926206

  20. Determinants of community structure of zooplankton in heavily polluted river ecosystems

    PubMed Central

    Xiong, Wei; Li, Jie; Chen, Yiyong; Shan, Baoqing; Wang, Weimin; Zhan, Aibin

    2016-01-01

    River ecosystems are among the most affected habitats globally by human activities, such as the release of chemical pollutants. However, it remains largely unknown how and to what extent many communities such as zooplankton are affected by these environmental stressors in river ecosystems. Here, we aim to determine major factors responsible for shaping community structure of zooplankton in heavily polluted river ecosystems. Specially, we use rotifers in the Haihe River Basin (HRB) in North China as a case study to test the hypothesis that species sorting (i.e. species are “filtered” by environmental factors and occur at environmental suitable sites) plays a key role in determining community structure at the basin level. Based on an analysis of 94 sites across the plain region of HRB, we found evidence that both local and regional factors could affect rotifer community structure. Interestingly, further analyses indicated that local factors played a more important role in determining community structure. Thus, our results support the species sorting hypothesis in highly polluted rivers, suggesting that local environmental constraints, such as environmental pollution caused by human activities, can be stronger than dispersal limitation caused by regional factors to shape local community structure of zooplankton at the basin level. PMID:26912391

  1. Determinants of community structure of zooplankton in heavily polluted river ecosystems

    NASA Astrophysics Data System (ADS)

    Xiong, Wei; Li, Jie; Chen, Yiyong; Shan, Baoqing; Wang, Weimin; Zhan, Aibin

    2016-02-01

    River ecosystems are among the most affected habitats globally by human activities, such as the release of chemical pollutants. However, it remains largely unknown how and to what extent many communities such as zooplankton are affected by these environmental stressors in river ecosystems. Here, we aim to determine major factors responsible for shaping community structure of zooplankton in heavily polluted river ecosystems. Specially, we use rotifers in the Haihe River Basin (HRB) in North China as a case study to test the hypothesis that species sorting (i.e. species are “filtered” by environmental factors and occur at environmental suitable sites) plays a key role in determining community structure at the basin level. Based on an analysis of 94 sites across the plain region of HRB, we found evidence that both local and regional factors could affect rotifer community structure. Interestingly, further analyses indicated that local factors played a more important role in determining community structure. Thus, our results support the species sorting hypothesis in highly polluted rivers, suggesting that local environmental constraints, such as environmental pollution caused by human activities, can be stronger than dispersal limitation caused by regional factors to shape local community structure of zooplankton at the basin level.

  2. Geographic structure and host specificity shape the community composition of symbiotic dinoflagellates in corals from the Northwestern Hawaiian Islands

    NASA Astrophysics Data System (ADS)

    Stat, Michael; Yost, Denise M.; Gates, Ruth D.

    2015-12-01

    How host-symbiont assemblages vary over space and time is fundamental to understanding the evolution and persistence of mutualistic symbioses. In this study, the diversity and geographic structure of coral-algal partnerships across the remote Northwestern Hawaiian Islands archipelago was investigated. The diversity of symbionts in the dinoflagellate genus Symbiodinium was characterised using the ribosomal internal transcribed spacer 2 (ITS2) gene in corals sampled at ten reef locations across the Northwestern Hawaiian Islands. Symbiodinium diversity was reported using operational taxonomic units and the distribution of Symbiodinium across the island archipelago investigated for evidence of geographic structure using permutational MANOVA. A 97 % sequence similarity of the ITS2 gene for characterising Symbiodinium diversity was supported by phylogenetic and ecological data. Four of the nine Symbiodinium evolutionary lineages (clades A, C, D, and G) were identified from 16 coral species at French Frigate Shoals, and host specificity was a dominant feature in the symbiotic assemblages at this location. Significant structure in the diversity of Symbiodinium was also found across the archipelago in the three coral species investigated. The latitudinal gradient and subsequent variation in abiotic conditions (particularly sea surface temperature dynamics) across the Northwestern Hawaiian Islands encompasses an environmental range that decouples the stability of host-symbiont assemblages across the archipelago. This suggests that local adaptation to prevailing environmental conditions by at least one partner in coral-algal mutualism occurs prior to the selection pressures associated with the maintenance of a symbiotic state.

  3. The structure and functions of bacterial communities in an agrocenosis

    NASA Astrophysics Data System (ADS)

    Dobrovol'skaya, T. G.; Khusnetdinova, K. A.; Manucharova, N. A.; Balabko, P. N.

    2016-01-01

    The most significant factor responsible for the specific taxonomic composition of the bacterial communities in the agrocenosis studied was found to be a part or organ of plants (leaves, flowers, roots, fruits). A stage of plant ontogeny also determines changes of taxa. In the course of the plant growth, eccrisotrophic bacteria are replaced by hydrolytic ones that belong to the group of cellulose-decomposing bacteria. Representatives of the proteobacteria genera that are difficult to identify by phenotypic methods were determined using molecular-biological methods. They were revealed only on oat leaves in the moist period. As the vetch-oat mixture was fertilized with BIOUD-1 (foliar application) in the phyllosphere of both oats and vetch, on all the plant organs, representatives of the Rhodococcus genus as dominants were isolated. This fact was related to the capability of bacteria to decompose the complex aromatic compounds that are ingredients of the fertilizers applied. Another positive effect for plants of the bacterial communities forming in agrocenoses is the presence of bacteria that are antagonists of phytopathogenic bacteria. Thus, in agrocenoses, some interrelationships promoting the growth and reproduction of plants are formed in crop plants and bacteria.

  4. Can microcystins affect zooplankton structure community in tropical eutrophic reservoirs?

    PubMed

    Paes, T A S V; Costa, I A S; Silva, A P C; Eskinazi-Sant'Anna, E M

    2016-06-01

    The aim of our study was to assess whether cyanotoxins (microcystins) can affect the composition of the zooplankton community, leading to domination of microzooplankton forms (protozoans and rotifers). Temporal variations in concentrations of microcystins and zooplankton biomass were analyzed in three eutrophic reservoirs in the semi-arid northeast region of Brazil. The concentration of microcystins in water proved to be correlated with the cyanobacterial biovolume, indicating the contributions from colonial forms such as Microcystis in the production of cyanotoxins. At the community level, the total biomass of zooplankton was not correlated with the concentration of microcystin (r2 = 0.00; P > 0.001), but in a population-level analysis, the biomass of rotifers and cladocerans showed a weak positive correlation. Cyclopoid copepods, which are considered to be relatively inefficient in ingesting cyanobacteria, were negatively correlated (r2 = - 0.01; P > 0.01) with the concentration of cyanotoxins. Surprisingly, the biomass of calanoid copepods was positively correlated with the microcystin concentration (r2 = 0.44; P > 0.001). The results indicate that allelopathic control mechanisms (negative effects of microcystin on zooplankton biomass) do not seem to substantially affect the composition of mesozooplankton, which showed a constant and high biomass compared to the microzooplankton (rotifers). These results may be important to better understand the trophic interactions between zooplankton and cyanobacteria and the potential effects of allelopathic compounds on zooplankton. PMID:26959954

  5. Acquisition and structuring of midgut bacterial communities in gypsy moth (Lepidoptera: Erebidae) larvae.

    PubMed

    Mason, Charles J; Raffa, Kenneth F

    2014-06-01

    Insects are associated with a diversity of bacteria that colonize their midguts. The extent to which these communities reflect maternal transmission, environmental acquisition, and subsequent structuring by the extreme conditions within the insect gut are poorly understood in many species. We used gypsy moth (Lymantria dispar L.) as a model to investigate interactions between egg mass and environmental sources of bacteria on larval midgut communities. Egg masses were collected from several wild and laboratory populations, and the effects of diet, initial egg mass community, and internal host environment were evaluated using 454 16S-rRNA gene pyrosequencing. Wild populations were highly diverse, while laboratory-maintained egg masses were associated with few operational taxonomic units. As larvae developed, their midgut bacterial communities became more similar to each other and the consumed diet despite initial differences in egg mass-associated bacteria. Subsequent experiments revealed that while midgut membership was more similar to bacteria associated with diet than with egg mass-associated bacteria, we were unable to detect distinct, persistent differences attributable to specific host plants. The differences between foliar communities and midgut communities of larvae that ingested them were owing to relative changes in populations of several bacteria phylotypes. We conclude that gypsy moth has a relatively characteristic midgut bacterial community that is reflective of, but ultimately distinct from, its foliar diet. This work demonstrates that environmental acquisition of diverse microbes can lead to similar midgut bacterial assemblages, underscoring the importance of host physiological environment in structuring bacterial communities. PMID:24780292

  6. Comparing Metabolic Functionalities, Community Structures, and Dynamics of Herbicide-Degrading Communities Cultivated with Different Substrate Concentrations

    PubMed Central

    Gözdereliler, Erkin; Boon, Nico; Aamand, Jens; De Roy, Karen; Granitsiotis, Michael S.; Albrechtsen, Hans-Jørgen

    2013-01-01

    Two 4-chloro-2-methylphenoxyacetic acid (MCPA)-degrading enrichment cultures selected from an aquifer on low (0.1 mg liter−1) or high (25 mg liter−1) MCPA concentrations were compared in terms of metabolic activity, community composition, population growth, and single cell physiology. Different community compositions and major shifts in community structure following exposure to different MCPA concentrations were observed using both 16S rRNA gene denaturing gradient gel electrophoresis fingerprinting and pyrosequencing. The communities also differed in their MCPA-mineralizing activities. The enrichments selected on low concentrations mineralized MCPA with shorter lag phases than those selected on high concentrations. Flow cytometry measurements revealed that mineralization led to cell growth. The presence of low-nucleic acid-content bacteria (LNA bacteria) was correlated with mineralization activity in cultures selected on low herbicide concentrations. This suggests that LNA bacteria may play a role in degradation of low herbicide concentrations in aquifers impacted by agriculture. This study shows that subpopulations of herbicide-degrading bacteria that are adapted to different pesticide concentrations can coexist in the same environment and that using a low herbicide concentration enables enrichment of apparently oligotrophic subpopulations. PMID:23124226

  7. Vegetation composition and soil microbial community structural changes along a wetland hydrological gradient

    NASA Astrophysics Data System (ADS)

    Balasoo