Variations mensuelles de la structure de communautés benthiques littorales d'eau douce en climat froid

Abstract

Monthly variations of macrobenthic communities were studied in three sites and during 13 months in the littoral zone of the St-Lawrence River (Qu6bec) where there are steep seasonal gradients of temperature and formation of an ice-foot during the long hivernal period. There is a good spatial distinction between the three benthic communities for all the year, except with the diversity index. Our results confirm the principal conclusions of precedent spatial and/or seasonal studies concerning means and temporal variability of uni-and multidimensional descriptors of community structure. Principal temporal discontinuities are observed during spring and are mainly explained by reproduction of dominant species, by migration of Gastropods between macrophytes and sediments and by emergence of Chironomids. During the six months of the hivernal period, there is a regular diminution of spatial heterogeneity in the littoral zone, temporal variations are weak and ice-foot do not affect community profiles. However, differences between thermal regime of the two years explain important variations at the community and at the population level. This inter-annual variations of the communities organisation are probably slowly compensated by interspecific competition as they were slowly compensated by intra-and interspecific competition at the population level.