Impact of Beach Nourishment on Distribution of Emerita Talpoioa, the Common Mole Crab

The ecological impact of beach nourishment on the common mole crab, Emerita talpoioa, determined through population census surveys, was found to be a redistribution of the organisms along the beach rather than in increase in population mortality. Reductions in population densities at and immediately adjacent to the downcurrent side of the point of discharge were recorded. The population depression was restricted to a 200-ft (6.10-m) section of the beach adjacent to the point of the discharge. Population 600—1,000 ft (183—305 m) down the beach in the direction of the longshore current increased, indicating a migration of mole crabs in response to nourishment. Tidal, wave, and current motions were found to play an essential role in reducing the mortality of the mole crabs and permitting migrations associated with beach nourishment. Population numbers at the discharge site recovered within a few tidal cycles.