Thursday, May 29, 2008 - 3:45 PM
598

Do benthic cyanobacteria and filamentous chlorophytes affect macroinvertebrate communities in a large river?

Anne-Marie Tourville Poirier1, Antonella Cattaneo1, and Christiane Hudon2. (1) Biology, Université de Montréal, C.P. 6128, succ. Centre Ville, Montreal, QC H3C 3J7, Canada, (2) Water Science and Technology Branch, Environment Canada, 105 McGill Street, Montreal, QC H2Y 2E7, Canada

Proliferations of the benthic cyanobacterium Lyngbya wollei and filamentous chlorophytes have been increasingly observed in shallow, slow-flowing fluvial lakes of the St. Lawrence River (Quebec, Canada). We determined the effect of vegetation biomass and composition on the phytophilous macroinvertebrate communities. In 2006, we sampled 12 sites corresponding to habitats dominated either by submerged macrophytes, filamentous green algae, benthic cyanobacteria or a combination of those three. Macroinvertebrates were sampled with a D-frame net (mesh size 500 µm) and a Plexiglas box (5.7 L). Physical (temperature, conductivity, transparency), chemical (nutrients concentrations) and biological (biomass of algae and vascular plants) characteristics were also measured at each site. Maximum densities of macroinvertebrates were observed at sites characterized by important biomass of vegetation (>350 g/m² dry mass), high conductivity (>200 μS/cm),high total nitrogen (>650 mg/L) and suspended matter (>5 mg/L) concentrations. Presence of benthic cyanobacteria and filamentous green algae increased macroinvertebrate densities. Macroinvertebrate composition differed among vegetation types. Amphipods and ostracods were most abundant on filamentous cyanobacteria whereas oligochetes and copepods were present in high densities in chlorophytes. Vegetation biomass and composition exerted a significant influence on density and composition of macroinvertebrates, with consequences on fish food availability and quality.


Web Page: cyanobacteria, macroinvertebrates, filamentous algae

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