Refuges for infaunal bivalves from blue crab, Callinectes sapidus (Rathbun), predation in Chesapeake Bay

Abstract

Monthly field sampling in the Choptank River, Chesapeake Bay, revealed rapid increases in population densities of infaunal bivalves in winter and spring followed by a decline in summer, presumably as a result of increased predation. Spat settlement of Mya arenaria L. occurred predominately in late fall and winter, declining in early spring. Macoma balthica (L.) spat settled primarily in spring. Spat of Macoma mitchelli Dall and Mulinia lateralis (Say) were found throughout most of the year. Field studies revealed a tendency for larger Mya arenaria, Macoma balthica, and M. mitchelli to be found deeper in the sediment. Laboratory studies tested the effectiveness of possible refuges within the sediment in protecting the soft clam, Mya arenaria, from blue crab ( Callinectes sapidus Rathbun) predation. Mya arenaria living below 10 cm were foraged for by blue crabs less effectively than those living closer to the surface. In the field, soft clams which settled in the fall were found living below 10 cm by the following May, reaching their maximum burial depth of 25 cm in June–July. An artificial plant structure also afforded some degree of protection from blue crabs in laboratory experiments: sparse and dense assemblages of artificial plants allowed higher survival of M. arenaria compared with control treatments. The protection afforded infaunal bivalves by these spatial or structural refuges is not absolute, although living deep within the sediment or within vegetation beds reduces the risk of predation in comparison to living near the sediment surface or in unvegetated areas.