Influence of freshwater inflow on reproductive capacity of the mud crab Eurypanopeus depressus inhabiting oyster reefs

Oyster reefs provide structural habitat for resident crabs and fishes, the planktonic larvae of which rely on estuarine transport/retention mechanisms to ensure settlement and subsequent recruitment to reefs. During periods of high freshwater inflow, larvae can be advected downstream and flushed out onto the continental shelf, resulting in an apparent reduction of larval supply within the estuary. However, reduced larval densities in estuaries might also result from decreased reproductive capacity, as dilute salinities on reefs upstream stress adult crabs. This study examined the reproductive capacity of the mud crab Eurypanopeus depressus (Smith, 1869) in response to freshwater inflow using the percentage of ovigerous females present as an indicator. Reproductive capacity on reefs was compared between two sites located near the mouths of two tidal tributaries, each experiencing differing rates of freshwater inflow, and between wet and dry seasons. Abundances of juvenile and adult crabs were significantly reduced during the wet season and at the site experiencing greater freshwater inflow. Length-frequency data indicate that newly recruited juvenile crabs were much less abundant at the site experiencing higher rates of inflow. The percentage of ovigerous females present was also reduced during the wet season but only at the reef experiencing greater inflow. Furthermore, the percentage of ovigerous females present at this site was inversely related to freshwater inflow and positively related to salinity. We suggest that high rates of freshwater inflow and the concomitant reduction in salinity can limit reproductive capacity in the flatback mud crab E. depressus on oyster reefs. Nonetheless, even as reproduction may be inhibited on reefs experiencing high inflow, other reefs subjected to lesser inflow may continue to serve as a source of larvae.