Algal Ecology
Presiding: S Francoeur, Eastern Michigan University; J Greenwood, US Environmental Protection Agency
NB42B-01 10:30h
Divergence in periphytic algal assemblages on bryophyte and bedrock substrata: potential for differential response to environmental variation
Algae grow on a variety of substrata and their response to environmental variables may be substratum-dependent. To examine the potential effects of variation in nutrient and light availability on periphyton from different substrata, algal biovolume and assemblage composition were examined on moss, liverwort and bedrock. The comparison was conducted in one nutrient-enriched and one control forested headwater stream, both sampled during months with high (May) and low (July) light availability. Assemblages were dominated by diatoms on all substrata; some filamentous reds and cyanophytes also occurred on bedrock. Ordination analysis (NMS) resulted in 3 axes explaining 86.6% of the variance in species composition and showed relatively strong separation across the three substrata. Bryophytes supported 2×106-fold greater total algal biovolume than bedrock (ANOVA p<0.0001). Periphyton biovolume was generally higher in May than July on all substrata. Two-way ANOVAs month (inferred light effect), stream (inferred nutrient effect)) on individual taxa indicated higher biovolume associated with higher light and lower biovolume associated with higher nutrient concentrations for some taxa, but effects were inconsistent across substratum types. Thus, variability in substratum types in headwater streams appears to support greater diversity of periphyton and response to environmental change than would be observed from a single substratum.
NB42B-02 10:45h
Diel changes in stream periphyton extracellular enzyme activity throughout community development on inert and organic substrates
We tested the hypothesis that algal photosynthesis in stream periphyton communities would influence the activities of extracellular enzymes produced by associated heterotrophic bacteria and fungi to acquire organic compounds and inorganic nutrients. We approached this question by looking for diurnal variation in activities of four extracellular enzymes in periphyton communities that were grown on either inert (glass fiber filters) or organic (leaves) substrata that there were incubated in stream-side channels that were either open to full sun or shaded. Substrata were subsampled for β -glucosidase, alkaline phosphotase, leucine-aminopeptidase, and phenol oxidase activities at 3-5 hr. intervals over two consecutive diurnal cycles that were repeated at an early and later stage of periphyton community development. Activities of all enzymes displayed diurnal periodicity but the strength of the diurnal effects depended largely on the substrate type and stage of community development. The most consistent diurnal change was observed with phenol oxidase activity with significantly greater (p<0.05) activities being observed in during the day for both stages of community development and for both substrate types. It is likely that oxygen produced by algal photosynthesis is driving the activity of this oxidative enzyme and that algae might indirectly influence the decomposition of phenolic compounds.
NB42B-03 11:00h
Bacterial and Fungal Responses to Algal Photosynthesis in Natural Wetland Periphyton
Microbial communities associated with plant detritus are composed of a diverse assemblage of autotrophic and heterotrophic microbes, including algae, bacteria, and fungi. This study examined the potential for rapid, photosynthetically-mediated interactions among microbes inhabiting submerged litter of Typha angustifolia. We grew natural periphyton communities (containing algae, bacteria, and fungi) on submerged Typha litter in a local wetland, and then manipulated photosynthesis by controlling light (0 or 400 Μmol m-2 s-1 PAR) while simultaneously quantifying rates of algal (14C-bicarbonate), bacterial (3H-leucine) and fungal (14C-acetate) productivity. Algal productivity was 50 to 100 fold greater at the high light intensity than at the low light intensity (p < 0.001). In addition, both bacterial (p < 0.001) and fungal (p = 0.005) productivities were significantly increased under high light intensities. The strong heterotrophic responses to light suggest that periphytic algal photosynthesis stimulated the productivities of litter-associated bacteria and fungi. Thus, microbial autotrophs may directly influence heterotrophic decay processes in wetland ecosystems.
NB42B-04 11:15h
Predicting Diatom Assemblages in Minimally-Impacted Streams Using a New Hybrid Modelling Approach
The expected taxonomic composition in minimally-impacted streams can be predicted using linear discriminant analysis (LDA) and environmental variables that are relatively independent of human activities. However, many biological responses to ecological gradients are non-linear. A hybrid approach combining LDA with nonlinear predictions made by recursive partitioning was applied using a Bayesian methodology. Diatom assemblages were used to classify reference sites throughout the western United States using a self-organizing map clustering technique. Predictive models for the classes were then developed using LDA, recursive partitioning, and the new hybrid method. Predictive models were evaluated using the ratio of correct-to-incorrect classifications, weighted by the confidence of each prediction. The hybrid method outperformed both LDA and recursive partitioning. Confidence-weighted ratios were 1.39 for the hybrid method, 1.15 for recursive partitioning, and 1.05 for LDA. Temperature was the most important linear predictor of diatom assemblages. Stream flashiness and precipitation were among the most important nonlinear predictors. Our results suggest that nonlinear determinants of diatom assemblages are important and that our hybrid method improves predictions of the expected conditions in reference habitats that are used in environmental assessments.
NB42B-05 11:30h
The Effects of Bryophyte Morphology on Epiphytic Diatom Distribution in the Great Smoky Mountains National Park
Diatoms and aquatic bryophytes have specific habitat requirements and are easily accessible in the field, making them ideal taxa for assessing water quality and environmental change. Although they both inhabit the same substrates within streams, there is a dearth of information regarding the relationship between these two indicator organisms. With this study, we examined the relationship between bryophytes and their epiphytic diatom communities from streams in the Great Smoky Mountains National Park. We hypothesized that bryophyte morphologies with more crevices between leaves would provide algae with a more protected micro-environment, resulting in a higher density of diatoms on these taxa compared to bryophytes with greatly exposed leaves. In addition, we also expect that bryophytes rich in crevices will have a high relative abundance of non-rheophilic taxa. Diatom community structure on bryophytes was determined using light microscopy. Using scanning electron microscopy, bryophytes were examined to compare the distribution and density of diatoms on the abnate and adnate surfaces of leaves. Preliminary results indicate that diatom density is not correlated with bryophyte species.
NB42B-06 11:45h
Rapid Changes In Carbon-13 During Periphyton Biomass Development
Stable isotopes are widely used to infer trophic relationships with little attention paid to temporal variability at the base of the food web. We examined the link between biomass development and temporal changes in the carbon-13 content of periphyton, sampling periphyton that developed on bare ceramic tiles at four sites on a weekly basis for two months. Periphyton became enriched in carbon-13 at all sites as biomass increased on the tiles. Delta values increased from -26 to -19 in two weeks at one site, then declined precipitously after a large spate scoured periphyton biomass to low levels. Delta values increased once again as biomass built up on the tiles. Current velocity, measured on each sampling occasion, was uncorrelated with temporal changes in carbon-13 but was related to site-to-site differences. The effect of developing periphyton biomass on carbon-13 appeared to be nonlinear, with the greatest increase in delta values occurring at low levels of biomass. Depletion of inorganic carbon within the periphyton matrix is the likely cause of increased carbon-13 fixation as periphyton biomass develops. Dynamic isotope composition in algal cells creates problems for the use of stable isotopes in identifying food sources in aquatic food webs.