Recent Research *         Potential impact of exotic crab species on juvenile bivalves

                The Asian shore crab, Hemigrapsus sanguineus, is a small brachyuran crab (Grapsidae) native to Japan and other western Pacific regions.  A recent introduction to the east coast of the U.S., it has undergone rapid range expansion since its first recorded appearance in New Jersey in 1988 and is frequently the most abundant crab of rocky intertidal areas where substrates range from large boulders to rock, cobble and broken shell.  An opportunistic omnivore, it feeds on a variety of resident organisms, including macroalgae, salt marsh grasses and small invertebrates such as amphipods, gastropods, bivalves, barnacles and polychaetes.  Because of this broad diet it has the potential to affect the populations of numerous resident species, either via competition for a common food source or through direct predation.

         Laboratory studies have shown that the nonindigenous Asian shore crab, Hemigrapsus sanguineus, readily consumes three species of commercial shellfish, Mytilus edulis, Mya arenaria and Crassostrea virginica. Although crabs can eat bivalves over a wide size range, they showed a marked preference for the smaller prey available (< 10 mm SL). Prey critical size limits exist for Mytilus and Crassostrea, but not Mya, possibly because of differences in shell characteristics among the three species. Crabs preferred Mya over both Mytilus and Crassostrea, and Mytilus was strongly preferred over Crassostrea in pairwise comparison tests. Hemigrapsus can consume large numbers of mussels daily (12.7 + 11.6 mussels d^-1; sexes pooled; N=69). Mussel consumption rates increased with size of the predator and male crabs consumed more mussels than similarly-sized female crabs. The high densities of Hemigrapsus that occur in the wild, their effectiveness as predators of juvenile bivalves and their large appetites suggest an important role for these predators in restructuring the prey communities in habitats into which they have been introduced.  

For additional information about potential impacts of the Asian shore crab invasion see:
    Pederson, J. (ed.). 2000. Marine Bioinvasions: Proceedings of the First National Conference, Jan. 24-27, 1999. Massachusetts 
    Institute of Technology Sea Grant Program. MIT Press. 427 pp.

* This project is being conducted by cooperative investigator: 

 Diane Brousseau Ph. D., Professor of Biology, Fairfield University Fairfield CT

 contact:  (email) diane.brousseau@noaa.gov       (voice) (203) 882-6507