The Dispersal of Gemma gemma. (Totten) and the Recolonization of Crab Foraging Pits in an Intertidal Sandflat

Abstract

Community structure in soft-bottom marine systems can be affected by biotic disturbances. At Tom's Cove, Assateague Island, Virginia, blue crabs and horseshoe crabs disturb the sediment in summer months by digging pits or depressions as they forage and mate. In this study, three hypotheses were tested to examine the recolonization dynamics of depressions by the dominant infaunal organism, the small, ovoviviparous bivalve, Gemma gemma (Totten). Hypothesis 1 predicted that the absolute and relative recolonization rates of G. gemma in depressions are greater in summer than in winter. Hypothesis 2 predicted that the movement of G. gemma is size- and age-selective, with a greater proportion of small, juvenile individuals found in depressions than in control areas. Hypothesis 3 predicted that dispersal of G. gemma is a passive phenomenon and occurs as individuals are moved by bedload transport. In summer 1986, hand-dug pits, simulating natural crab pits, were sampled over time to determine summer recolonization rates, and pitfall traps were employed to measure the sediment volume and number of G. gemma moving into depressions by bedload transport. Results from this study were compared with values from samples obtained in similar studies during winter months at the same site.