Drying of a temperate, intermittent river has little effect on adjacent riparian arthropod communities

Rivers and their adjacent riparian zones are intimately linked by fluxes of water, air masses, nutrients and organisms. Intermittent rivers constitute ideal systems to examine these linkages because they are characterised by alternating wet and dry phases, and hence, natural and contrasting variations occur in aquatic resources and environmental conditions. We addressed the effects of river drying on riparian communities by collecting ground-dwelling arthropods at three perennial sites and at four intermittent sites during a wet and a dry phase in the Albarine River (France). We first predicted that during dry phases, declines in aquatic resources and loss of water would create harsh environmental conditions and alter community structure and composition, due to decreases in predators and hygrophilous taxa. Second, we predicted that alternating wet and dry phases would enhance cumulative taxonomic richness over time owing to an increase in species turnover. We found similar decreasing temporal patterns in taxonomic richness and abundance at intermittent and perennial sites, indicating that river drying had no effect on the structure of riparian arthropod communities. Community composition at intermittent and perennial sites differed only during the dry phase, indicating that intermittent and perennial sites gained and lost different sets of taxa as the river dried. Nevertheless, species turnover did not differ between sites, while taxonomic richness was always higher at intermittent sites. Although some taxa were sensitive to river drying, the Albarine River supports rich and abundant riparian arthropod communities. While several studies have reported a strong dependence of riparian populations on aquatic resources, our results indicate that the effects of river drying on riparian arthropods at the community level are weak and discrete in time in the Albarine River.