Predation by the nonindigenous Asian shore crab Hemigrapsus sanguineus on macroalgae and molluscs

Prey selection and consumption of common molluscs and macroalgae by the Asian shore crab, Hemigrapsus sanguineus, were investigated in the laboratory. Crabs of three size classes (12-18, 19-25, 26-31 mm carapace width) collected from the rocky intertidal from May to November 1998, and were offered three mollusc species: the mussel Mytilus edulis, the clam Mercenaria mercenaria, and the snail Littorina littorea. Equal numbers of prey from three size classes or two species were offered concurrently to individual crabs. Crabs consumed small molluscs, large males opening larger molluscs than did females and smaller males. Male crabs consumed both mussels and clams. Females opened only mussels, but ate flesh from previously opened clams. Very few L. littorea were consumed. The macroalgae Codium fragile ssp. tomentosoides, Enteromorpha spp., Chondrus crispus, Fucus spp., and Ascophyllum nodossum were presented to individual crabs separately to determine consumption rates and together to ascertain species preference. Crabs preferred the green algae C. fragile ssp. tomentosoides and Enteromorpha spp.