Responses and adaptative strategy of epilithic algae communities to different hydrological regimes

Responses of epilithic algal communities were studied in a regulated river presenting two different hydrological regimes. Upstream of the: Escale reservoir, the hydrological regime is characterized by a flow compensation with discharge continuous release responsible for the most significant disturbances occurring in the regulated River Durance. Downstream of this reservoir, the river presents a stable and low compensation flow. The analysis of the epilithic algal communities submitted to contrasting flow regimes has shown responses at different levels: a) at the level of the whole community, a global response by changes in species richness and abundance, as well as in community structure; b) at the level of the: particular taxonomic groups, such as, for instance, a more important development of filamentous green algae, observed in the downstream reach; c) at the species level: the acquisition, by some diatoms, of an architectural type adapted to the now regime. ((C) Academie des sciences / Elsevier, Paris.)