Identification: Adults are small, about an inch and a half in shell width. Square shell. Light and dark bands on legs.
The first sighting of the Asian shore crab in the United States was at Townsend Inlet, Cape May County, New Jersey, in 1988. Though the source is unknown, it is likely that the crabs were discharged as larvae from the ballast water of a cargo ship. The transfer of larvae around the world in ballast tanks is a form of "ocean roulette," with each ship a potential chamber ready to discharge a new, unwanted species.
Along the Atlantic intertidal coastline from Maine to North Carolina, this crab is now breeding and increasing rapidly in number. Because it tolerates a wide range of environmental conditions, it seems all too likely to continue to multiply and to spread. Because it is not a picky eater, it outcompetes native species such as crabs, fish, and shellfish for food — or it eats them, being an opportunistic omnivore that feeds on algae, saltmarsh grass, larval and juvenile fish, and small invertebrates such as amphipods, gastropods, bivalves, barnacles, and worms. That wide-ranging appetite and the growing population threaten both coastal ecosystems and aquaculture operations.
This invasive shore crab takes over habitats normally occupied by native mud crabs. It can compete with larger species, such as the blue crab, rock crab, lobster, and even another invader, the European green crab. The Asian shore crab breeds from May to September, twice as long as many native crabs. Females can produce 50,000 eggs per clutch, and 3 to 4 clutches per season. Suspended in tidal water for a month before developing into juvenile crabs, the larvae can be transported over great distances — a possible means of new introductions.
