The present thesis contributes to the understanding of the fonction of glacial stream ecosystems. The six parts of this work examine the relationships between the macroinvertebrate communities and the environmental conditions in a small glacial catchment of the Swiss Alps (the Mutt, Valais) and along the longitudinal gradient of three glacial streams of the Swiss and the French Alps: the Mutt and the Rhone (Valais, Switzerland) and the Romanche (Hautes-Alpes, France).

The first part is a study of the macroinvertebrate drift in contrasted streams of the Mutt basin, in relation to their physico-chemical characteristics. It underlines the high diversity of benthic communities, strongly correlated with the environmental conditions. In kryal (glacial) streams, where harsh conditions prevail (low water temperatures, high suspended sediment concentrations and important dial flow fluctuations during the warm season), the faunal diversity and abundance are low. The krenal (groundwater-fed) streams, characterised by more harmless environmental conditions shelter more diversified and dense macroinvertebrate communities. These tributaries of the Mutt do not contribute markedly to the faunal enrichment of the main glacial channel, but favour the coexistence of diversified macroinvertebrate communities in a rather small catchment area. Therefore these tributaries play an important part in the biodiversity of the glacial catchment.

The second part compares benthic and drifting macroinvertebrate assemblages sampled with two different techniques (kick sampling and drift sampling respectively) in glacial and groundwater-fed streams of the Mutt basin. The richness estimates from both techniques, calculated by means of rarefaction method, are similar for the groundwater-fed streams but significantly higher in the benthos of kryal streams. The relative composition of the taxonomie assemblages also vary according to the sampling method. Both methods can be used to assess the typology of the streams of this catchment, but benthic samples provide a more complete taxonomie inventory. [...]