Abstract
Spatio-temporal variations of macrobenthic community structure were studied in the littoral zone of the Saint-Lawrence River (Quebec). Its thermal regime is characterized by steep seasonal gradients from April to November and by a long ice-cover period with formation of an icefoot. Six sites were sampled each season for one year. Temporal variations are less important than spatial variations. They are mainly seasonal and depend on emergence and recruitment periods and on migrations but there are also long-term variations. An increase of the mean diversity index of sites corresponds to an increase of seasonal variations of community profile and to a decrease of seasonal variations of organism abundance; it is explained by a better exploitation of benthic resources rather than by environment stability. Spatial variations of community structure depend mainly on vegetation abundance. There is no faunal zonation corresponding to the icefoot action. In sites where Gastropods are abundant, icefoot does not change community profile but it explains diminutions of density and of species diversity. Chironomids are little affected by this phenomenon.
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