Differential predation and growth rates of bay scallops within a seagrass habitat

The bay scallop, Argopecten irradians, is a common and commercially important bivalve species residing in shallow marine ecosystems dominated by seagrasses. However, unlike most bivalves, scallops have the ability to move considerable distances within and among habitats. Consequently, their adult distribution may not be set by larval settlement patterns. In St. Joseph Bay, FL, USA, scallops were significantly more abundant at edges of turtle grass (Thalassia testudinum) beds (x=0.75 m^-2) than in their interior (x=0.375 m^-2) or in nearby unvegetated sediments (x=0.00). This difference in habitat use was shown by field experiments to have two important consequences. First, scallops living along edges of T. testudinum beds experience significantly higher predation potential (>20% loss to predation day^-1) than scallops living in the interior of grass beds or on open sediment (<5% predation loss day^-1). Second, scallops living along the edge of grass beds showed significantly higher growth rates (0.031 mg dry wt. day^-1) than individuals living on open sediment (0.012) or in the interior of beds (0.019). Therefore, individual scallops appear to trade off higher predation risk for increased growth rates.