Original paper

The response of invertebrates in moss and in gravel to water level fluctuations in a Quebec stream

Cattaneo, Antonella; Cloutier, Louise Méthot


To assess the response of stream communities to water level fluctuations, we measured the biomass and taxonomic composition of invertebrates colonizing substrata at varying depths, and thus more or less frequently exposed as flow declined. We compared the response of invertebrate communities in the moss Fontinalis dalecarlica and in gravel throughout the growing season in a small Québec stream. Depth explained a large proportion of the variation in invertebrate biomass in moss for all dates (from 50 – 80 %). Invertebrate biomass was lower on shallow mosses frequently exposed than on deeper ones, which remained submerged. In contrast, depth was never significantly related to invertebrate biomass in gravel. A significant fraction of the variation in invertebrate taxonomic composition was explained by substratum type (moss versus gravel) and exposure (estimated through depth) for all sampling dates (Canonical Correspondence Analysis). In particular, grazers were more common and abundant in moss than in gravel, suggesting a stronger reliance on periphyton on the part of moss-dwelling communities, and consequently greater vulnerability to periphyton reduction upon exposure. Invertebrates inhabiting gravel appear less affected by reductions in water level as they can burrow in the substratum at low flow. Gravel habitats tend to be lower on the streambed than moss, and consequently emerge less often. In view of forecasts of increased variability in stream water levels arising from climate changes, our study stresses the need to consider the differential vulnerability of communities on different substrata to hydrological disturbances.


periphytonaquatic insectswater level fluctuationdepthexposure