Bacterial community structure along the Adour estuary (French Atlantic coast): influence of salinity gradient versus metal contamination

Abstract

Bacterial communities in estuarine ecosystems are exposed to strong changes in environmental conditions. The mixing of seawater and freshwater, the variations in residence time, the transportation of either dissolved or suspended organic and inorganic material, as well as modifications due to climatic conditions may induce specific patterns of bacterial abundance, diversity and activity in these ecosystems. Differences in bacterial abundances have been demonstrated along the salinity gradients in the Rhone estuary and the Columbia River (Crump et al. 1999, Troussellier et al. 2002). The sharp phylogenetic succession that occurs in fresh to saltwater transition regions is accompanied by profound physiological changes at the community level (del Giorgio & Bouvier, 2002). However, available data on bacterial diversity have led to inconsistent conclusions. Some studies have demonstrated how freshwater and marine bacterioplankton communities mix along estuarine gradients, concluding that bacterioplankton in the estuarine zone appears to be