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Diatom Communities (diatom + community)

Distribution by Scientific Domains

Life Sciences	93%

Selected Abstracts

Are diatoms good integrators of temporal variability in stream water quality?

FRESHWATER BIOLOGY, Issue 4 2008
ISABELLE LAVOIE
Summary 1. Although diatoms have been used for many decades for river monitoring around the world, studies showing evidence that diatoms integrate temporal variability in water chemistry are scarce. 2. The purpose of this study was to evaluate the response of the Eastern Canadian Diatom Index (IDEC: Indice Diatomées de l'Est du Canada) with respect to temporal water chemistry variability using three different spatio-temporal data sets. 3. Along a large phosphorus gradient, the IDEC was highly correlated with averaged water chemistry data. Along within-stream phosphorus gradients, the IDEC integrated phosphorus over various periods of time, depending on the trophic status of the site studied (Boyer, Nicolet or Ste. Anne river) and variability in nutrient concentration. 4. In the Ste. Anne River, where nutrient concentrations were low and generally stable, an input of phosphorus induced a rapid change in diatom community structure and IDEC value within the following week. In the mesotrophic Nicolet River, the observed integration period was approximately 2 weeks. Diatom communities in the eutrophic Boyer River appeared to be adapted to frequent and significant fluctuations in nutrient concentrations. In this system, the IDEC therefore showed a slower response to short term fluctuations and integrated nutrient concentrations over a period of 5 weeks. 5. Our results suggest that the integration period varies as a function of trophic status and nutrient concentration variability in the streams. Oligotrophic streams are more sensitive to nutrient variations and their diatom communities are directly altered by nutrient increase, while diatom communities of eutrophic rivers are less sensitive to nutrient fluctuations and major variations take a longer time to be integrated into index values. 6. The longer integration period in the eutrophic environment may be attributed to the complexity of the diatom community. The results from this study showed that the diversity and evenness of the communities increased with trophic status. [source]

Responses of biofilms to combined nutrient and metal exposure

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2002
Núria Ivorra
Abstract Numerous studies have reported marked sensitivities of diatom species to phosphate and organic pollution but have ignored interactions with other common contaminants. The aim of the present study was to investigate the single and joint effects of increased phosphate and metal (cadmium, zinc) concentrations on benthic diatom communities. Microalgal biofilms from a relatively unpolluted stream were exposed in the laboratory to Zn, Cd, and P, separately and in combination, in concentrations found at a polluted stream in the same catchment. The Zn concentration reduced algal growth in biofilms more than the Cd concentration. Phosphate compensated for the single effect of each metal but not for their combined effects. Diatom community changes were evaluated using water quality indices based on the empirical sensitivities of taxa to nutrients (TDI) and organic pollution (%PTV). Phosphate exposure resulted in an increase of the eutrophy rank and presumed pollution-tolerant taxa. In contrast, exposure to Zn, Zn + Cd, and Zn + Cd + P caused a marked reduction of the TDI and %PTV community values. The successional trends in the laboratory matched the observed differences in microphyte communities in the reference and polluted river stations. However, the autoecology of the species present also revealed that the resulting composition of diatom communities cannot be attributed solely to the direct toxic effects of metal and nutrients and their interaction. Observed changes in the relative abundance of species are also determined by their growth form and microdistribution in biofilms. [source]

Are diatoms good integrators of temporal variability in stream water quality?

Assembly rules and community models for unicellular organisms: patterns in diatoms of boreal streams

FRESHWATER BIOLOGY, Issue 4 2005
JANI HEINO
Summary 1. Many studies have addressed either community models (e.g. Clementsian versus Gleasonian gradients) or assembly rules (e.g. nestedness, checkerboards) for higher plant and animal communities, but very few studies have examined different non-random distribution patterns simultaneously with the same data set. Even fewer studies have addressed generalities in the distribution patterns of unicellular organisms, such as diatoms. 2. We studied non-randomness in the spatial distribution and community composition of stream diatoms. Our data consisted of diatom surveys from 47 boreal headwater streams and small rivers in northern Finland. Our analytical approaches included ordinations, cluster analysis, null model analyses, and associated randomisation tests. 3. Stream diatom communities did not follow discrete Clementsian community types, where multiple species occur exclusively in a single community type. Rather, diatom species showed rather individualistic responses, leading to continuous Gleasonian variability in community composition. 4. Although continuous variability was the dominating pattern in the data, diatoms also showed significant nestedness and less overlap in species distribution than expected by chance. However, these patterns were probably only secondary signals from species' individualistic responses to the environment. 5. Although unicellular organisms, such as diatoms, differ from multicellular organisms in several biological characteristics, they nevertheless appear to show largely similar non-random distribution patterns previously found for higher plants and metazoans. [source]

Broad-scale environmental response and niche conservatism in lacustrine diatom communities

GLOBAL ECOLOGY, Issue 5 2010
Joseph R. Bennett
ABSTRACT Aim, (1) To resolve theoretical debates regarding the role of environment versus dispersal limitation, the conservatism of niches across distances and the prevalence of environmental specialists in diatom communities. (2) To provide guidance on the use of diatom communities and other microbial analogues to analyse ecological response to environmental change. Location, Eight hundred and ninety-one lakes in five regional datasets from north-western Europe and four regional datasets from north-eastern North America. Methods, Lacustrine diatom communities were analysed at three scales: inter-continental, intra-continental and regional. Nested partial redundancy analyses (RDAs) were used to determine spatial versus environmental components of community variation. Weighted-averaging (WA) regression and calibration, as well as logistic and quadratic regressions, were used to detect niche conservatism and the prevalence of environmental specialists. Results, Community patterns indicate that dispersal limitation acts predominantly at the inter-continental scale, while at the regional (less than c. 1,000,000 km2) scale, a single environmental variable (pH) explains more than five times the community variation as spatial (dispersal-related) variables. In addition, pH niche components appear to be conserved at the inter-continental scale, and environmental specialization does not impose relative rarity, as specialists apparently readily disperse to suitable environments. Main conclusions, Analysis at multiple scales is clearly important in determining the influences of community variation. For diatom communities, dispersal limitation acts most strongly at the broadest scales, giving way to environment at the scales considered by most analyses. The availability of a wide variety of propagules with consistent niches across regions indicates that diatom communities reflect the succession of taxa according to local environmental conditions, rather than disequilibrium with the environment or adaptation of local populations. While multi-scale analyses must be undertaken for other groups to resolve debates over community drivers and determine appropriate scales for prediction, for diatoms (and probably other microbial communities), responses to environmental change can be inferred using analogue datasets from large geographic areas. [source]

COMPARISON OF SIMPLE AND MULTIMETRIC DIATOM-BASED INDICES FOR GREAT LAKES COASTLINE DISTURBANCE,

JOURNAL OF PHYCOLOGY, Issue 3 2008
Euan D. Reavie
Because diatom communities are subject to the prevailing water quality in the Great Lakes coastal environment, diatom-based indices can be used to support coastal-monitoring programs and paleoecological studies. Diatom samples were collected from Great Lakes coastal wetlands, embayments, and high-energy sites (155 sites), and assemblages were characterized to the species level. We defined 42 metrics on the basis of autecological and functional properties of species assemblages, including species diversity, motile species, planktonic species, proportion dominant taxon, taxonomic metrics (e.g., proportion Stephanodiscoid taxa), and diatom-inferred (DI) water quality (e.g., DI chloride [Cl]). Redundant metrics were eliminated, and a diatom-based multimetric index (MMDI) to infer coastline disturbance was developed. Anthropogenic stresses in adjacent coastal watersheds were characterized using geographic information system (GIS) data related to agricultural and urban land cover and atmospheric deposition. Fourteen independent diatom metrics had significant regressions with watershed stressor data; these metrics were selected for inclusion in the MMDI. The final MMDI was developed as the weighted sum of the selected metric scores with weights based on a metric's ability to reflect anthropogenic stressors in the adjacent watersheds. Despite careful development of the multimetric approach, verification using a test set of sites indicated that the MMDI was not able to predict watershed stressors better than some of the component metrics. From this investigation, it was determined that simpler, more traditional diatom-based metrics (e.g., DI Cl, proportion Cl-tolerant species, and DI total phosphorus [TP]) provide superior prediction of overall stressor influence at coastal locales. [source]

Geographical patterns of micro-organismal community structure: are diatoms ubiquitously distributed across boreal streams?

OIKOS, Issue 1 2010
Jani Heino
A topic under intensive study in community ecology and biogeography is the degree to which microscopic, as well as macroscopic organisms, show spatially-structured variation in community characteristics. In general, unicellular microscopic organisms are regarded as ubiquitously distributed and, therefore, without a clear biogeographic signal. This view was summarized 75,years ago by Baas-Becking, who stated "everything is everywhere, but, the environment selects". Within the context of metacommunity theory, this hypothesis is congruent with the species sorting model. By using a broad-scale dataset on stream diatom communities and environmental predictor variables across most of Finland, our main aim was to test this hypothesis. Patterns of spatial autocorrelation were evaluated by Moran's I based correlograms, whereas partial regression analysis and partial redundancy analysis were used to quantify the relative importance of environmental and spatial factors on total species richness and on community composition, respectively. Significant patterns of spatial autocorrelation were found for all environmental variables, which also varied widely. Our main results were clear-cut. In general, pure spatial effects clearly overcame those of environmental effects, with the former explaining much more variation in species richness and community composition. Most likely, missing environmental variables cannot explain the higher predictive power of spatial variables, because we measured key factors that have previously been found to be the most important variables (e.g. pH, conductivity, colour, phosphorus, nitrogen) shaping the structure of diatom communities. Therefore, our results provided only limited support for the Baas-Becking hypothesis and the species sorting perspective of metacommunity theory. [source]

Rules for macroorganisms applied to microorganisms: patterns of endemism in benthic freshwater diatoms

OIKOS, Issue 4 2007
Cathy Kilroy
Ecological theory based on the dynamic equilibrium model (DEM) suggests that maintenance of endemic taxa is most likely in stable, unproductive environments. We tested whether this hypothesis, which was developed mainly using terrestrial plant examples, held when applied to distributions of benthic freshwater diatoms in New Zealand. Given current arguments for the ubiquity of microbial organisms, with distributions determined mainly by environmental tolerances, demonstration that distinctive taxa with evidently restricted distributions conform to theory applicable to larger organisms would lend support to the opposite point of view, that barriers to dispersal do exist. We examined diatom communities from over 320 sites representing the entire spectrum of freshwater habitats in New Zealand and assessed relative abundances of the main taxa present. Each taxon distinguished was assigned to one of five distribution categories ranging from cosmopolitan to endemic. We derived indices of disturbance and productivity for each site using the River Environment Classification (REC), a GIS-based classification system developed for New Zealand rivers. Diatom taxa assigned to endemic or distinctive potential endemic categories were significantly more abundant in low disturbance sites but occurred across a range of productivities. However, bogs and tarns, both of which fell mainly into low disturbance and productivity classes, were distinctive in supporting relatively high proportions of endemic and potential endemic diatoms. Thus our findings in general conformed to the patterns predicted by the DEM, thereby supporting the role of dispersal limitation in diatoms. At the same time, conformity with the DEM helps to explain the continued coexistence in New Zealand freshwaters of many common and apparently cosmopolitan taxa with endemic diatoms, since the DEM explanation for maintenance of endemism does not rely on geographic isolation of species. [source]

Are diatoms good integrators of temporal variability in stream water quality?

Multiproxy evidence of an early Holocene (8.2 kyr) climate oscillation in central Nova Scotia, Canada

JOURNAL OF QUATERNARY SCIENCE, Issue 7 2002
Professor Ian Spooner
Abstract An early Holocene lake sediment record from central Nova Scotia contains a minerogenic oscillation that is closely correlative with the 8.2 kyr event (ca. 8200 cal. yr BP), an event that has not been reported elsewhere in Atlantic Canada. A variety of biological and sedimentological indicators have been examined to characterise autochthonous and allochthonous changes that occurred during this time. The minerogenic upper oscillation (UO, ca. 8400 cal. yr BP) is marked by an increase in the chrysophyte:diatom ratio. Following the oscillation, the diatom community reflects a shift to more productive, less acidic conditions. The pollen record shows no major response to this short-lived event. Lithostratigraphic analyses indicates that the UO is characterised by an increase in clastic content, magnetic susceptibility and mean sediment grain size, all indicators of changing environmental conditions, most likely the result of regional cooling. The Taylor Lake record adds to a growing body of evidence for a widespread, hemispheric climate oscillation at 8.2 kyr. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Low reproductive success for copepods during a bloom of the non-aldehyde-producing diatom Cerataulina pelagica in the North Adriatic Sea

MARINE ECOLOGY, Issue 3 2008
Adrianna Ianora
Abstract Egg production rates and/or hatching success in the copepods Acartia clausi, Calanus helgolandicus and Temora longicornis were negatively affected by a late spring (May,June 2003) phytoplankton bloom in the North Adriatic Sea, dominated mainly by the large diatom Cerataulina pelagica. Highest total concentrations of 3.3·104 cells·ml,1 were located in the vicinity of the Po River, which also corresponded to the area where the highest numbers of phaeophorbides were measured (0.779, 0.528 and 0.419 ,g·l,1, respectively, compared to an average of the remaining stations of 0.183 ± 0.049 SD), suggesting some grazing on the bloom. Phytoplankton biomass in terms of carbon was dominated by diatoms, representing on average 42% of total phytoplankton carbon and more than 80% at several stations. Cerataulina pelagica, Cyclotella spp., Chaetoceros spp. and small unidentified centric diatoms dominated the diatom community numerically but C. pelagica was by far the dominant diatom in terms of carbon due to its large cell size. This species represented more than 60% of the diatom biomass at nine of the 14 stations sampled, and was absent only at one station, which was the most offshore station sampled during the cruise. Although polyunsaturated aldehydes (PUAs) were not detected, other oxylipins which are hydroxy and keto derivatives of eicosapentaenoic and docosahexaenoic acids that affect copepod reproduction were found in these samples. Hence, we can attribute the negative impact of diatoms not only to PUAs, as previously believed, but also to these compounds. This is the first direct evidence of the presence of oxylipins other than PUAs in marine blooms dominated by diatoms. [source]