Patterns in invertebrate and periphyton size distributions from navigationbuoys in the St. Lawrence River

For the purposes of conducting environmental assessments, it has been sugge sted that benthic size distributions could serve as complementary or altern ative measures to traditional taxonomic descriptions, which are labour inte nsive and require much expertise. Consequently, temporal patterns of invert ebrate and algal size distributions, along a trophic gradient from St. Lawr ence River navigational buoys, were investigated in this study. It was obse rved that the size distributions were not significantly related to physical or chemical parameters of the river, although variability in the data may have been too high to detect trophic effects, as indicated by Monte Carlo s imulations. Size spectra on buoys, despite the fact that protozoans were no t accounted for, had striking similarities with other complete size distrib utions (containing algae, protozoans and invertebrates) from stream (Cattan eo, 1993; characteristic size distributions of integral bethnic communities . Can. J. Fish aq uat. Sci. 38: 1255-1263), lake (Cattaneo, 1987; Size dist ribution in periphyton Can. J. Fish. Aquat. Sci. 44: 2025-2028) and marine littoral zones (Schwinghammer, 1981; Size spectra of bethnic communities in Laurantian streams. Can J. Fish. aquat. Sci. 50: 2659-2666). This suggests that size distributions, determined over broad size ranges, are relatively robust to environmental conditions and may be of limited use in assessing ecological degradation.