Long-term effects of salinity and disturbance regime on active and dormant crustacean communities

Abstract

In a large-scale and long-term outdoor mesocosm (400-liter) experiment, we studied the interacting effects of salinity and disturbance (hydrological) regime on the active and dormant crustacean communities of Mediterranean temporary wetlands (Camargue, southern France). Sixty-four mesocosms, inoculated with a regional species pool (mixed dormant egg banks), were exposed to a full factorial treatment combination of four salinity levels and four disturbance regimes during three consecutive years. Both in the active and dormant community component, considerable shifts in community composition occurred because of direct and probably also second-order effects of the treatments. All large branchiopod species had low long-term salinity tolerances and showed species-specific preferences for disturbance regimes according to their life cycle strategy. The highest salinity (5) was not limiting for cladocerans and ostracods, which thrived in the absence of the competitively stronger, predatory, and bioturbating large branchiopods. Copepods were negatively associated with salinity and coped better with the imposed biotic pressure. Zooplankton diversity and density peaked in intermediatedisturbance regimes, probably because only specialized species survived the high-disturbance regimes, whereas at low-disturbance frequencies high densities of predatory Triops controlled zooplankton communities. Although crustacean dormant egg banks can temporarily buffer against unfavorable conditions, persisting bad conditions may lead to their exhaustion within 4 to 10 yr. Predicted aridification (leading to more intense disturbance regimes) may result in the loss of late successional species (chydorids and ostracods), whereas salinization may wipe out sensitive freshwater species such as large branchiopods. © 2011, by the American Society of Limnology and Oceanography, Inc.