Effect of salinity on seasonal community patterns of Mediterranean temporary wetland crustaceans: A mesocosm study

Abstract

In a large‐scale outdoor mesocosm experiment we studied the effects of salinity on successional patterns, diversity, and relative abundances of Camargue (southern France) temporary pool crustaceans. Eighty mesocosms were inoculated with a mixed resting egg bank and exposed to four different salinity treatments (0.5, 1.0, 2.5, and 5.0 g L−1) for a period of 7 months. Salinity significantly altered crustacean communities hatching from the resting egg bank through a number of direct and indirect effects. Salinity had a significant negative effect on the establishment of large branchiopods and copepods. Both richness and density of cladocerans, especially chydorids, were positively related to salinity, possibly due to the absence of biotic interactions with large branchiopods at the highest salinity values. We hypothesize that the salinity‐mediated presence of the large branchiopod keystone group can shift the whole wetland regime from a zooplankton‐rich clear‐water state to a zooplankton‐poor turbid state. Crustacean succession was significantly altered by salinity, by slowing down development rates, population growth or maturation rates of some species. This suggests that in addition to salinity changes, any alteration of wetland hydroperiod (e.g., through aridification or inappropriate water management) could have a synergistic effect on community structure and diversity of invertebrate communities, including some keystone species.