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

Abstract

For the purposes of conducting environmental assessments, it has been suggested that benthic size distributions could serve as complementary or alternative measures to traditional taxonomic descriptions, which are labour intensive and require much expertise. Consequently, temporal patterns of invertebrate and algal size distributions, along a trophic gradient from St. Lawrence River navigational buoys, were investigated in this study. It was observed 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 simulations. Size spectra on buoys, despite the fact that protozoans were not accounted for, had striking similarities with other complete size distributions (containing algae, protozoans and invertebrates) from stream (Cattaneo, 1993; characteristic size distributions of integral bethnic communities. Can. J. Fish aquat. Sci. 38: 1255–1263), lake (Cattaneo, 1987; Size distribution 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.