Size Distribution of Epilithic Lotic Invertebrates and Implications for Community Metabolism

Abstract

The size structure of epilithic animal communities was examined in 12 streams of the Ottawa-Hull region, Ontario-Québec border. In all streams, the size distribution of invertebrates in late summer was approximately lognormal, with most animals <2 mm long (about 10 μg dry mass), but with most of the biomass in size classes >2 mm. Size structure differed significantly among streams, but these differences were not correlated with total invertebrate biomass or periphyton abundance. Normalized biomass spectra in all streams were peaked, unlike those reported for marine and freshwater benthic and planktonic communities. It is likely, however, that addition of bacterial, algal, and meiofaunal components to obtain spectra for the entire epilithic community may linearize the spectraaa, yielding approximately equal biomasses in logarithmic size classes. When combined with allometric relationships describing metabolism, the observed size spectra imply that metazoans <1 mm long make negligible contributions to production, consumption, or respiration of the epilithon.