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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Food Webs
GRAZING OF EPIPHYTON AND PRODUCTION OF FECAL PELLETS BY THE ISOPOD ASELLUS AQUATICUS .
A. Hargeby. Limnology, Department of Ecology, Lund University, S-22362 Lund, Sweden
The role of non-gastropod macroinvertebrates (e.g. crustaceans and insect larvae) as epiphyton grazers is less well known in lakes than in streams. Here, I show that the isopod Asellus aquaticus may function as a grazer on epiphyton in lentic submerged vegetation. Field surveys in three shallow, eutrophic lakes in Sweden and Latvia showed that A. aquaticus occurred at densities of 5 000 - 50 000 ind. per meter squared in dense stands of stoneworts, Chara spp. Biomass of A. aquaticus was similar to that of snails. In cage experiments, grazing by A. aquaticus reduced epiphyton biomass to 10 - 20% of control levels. Laboratory estimates of production of fecal pellets indicated that grazing rate by A. aquaticus is similar to that of three snail species: Lymnea peregra, Physa fontinalis and Bithynia tentaculata. In all four species, daily production of fecal pellets corresponded to 1.0 – 1.2 g DW per g animal AFDW. Fecal pellets made up a major proportion of particulate matter collected in sedimentation traps in stands of Chara spp. Stable isotope analysis are currently performed to examine the origin of sedimenting particles in the vegetation, and the position of A. aquaticus and snails in the food web.
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