Alaska Department of Fish and Game
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Invasive Species — European Green Crab (Carcinus maenas)
The European green crab is a concern to Alaska because it may have negative impacts on local commercial, personal use and subsistence fisheries and cause habitat disturbance. The species composition of rocky shore and soft-bottom communities, and the distribution, abundance, size, morphology, and behavior of prey populations can be dramatically altered when green crabs are present.
Although some infaunal organisms may benefit from the digging activities of green crab, eelgrass beds can be damaged, and newly settled juvenile green crabs prey heavily on the infauna, such as tubeworms, juvenile clams and juvenile crabs. Since eel grass beds are valuable habitat and provide refugia for juvenile salmonids, among other species, the establishment of green crab in Alaska waters could result in detrimental changes in intertidal ecosystem dynamics. Additionally, native clams, cockles, mussels, and snails are preferred prey for green crab; they also graze on some algaes, including the widely distributed Fucus sp. When green crabs are present, total exclusion of mussels in the rocky, low intertidal zone has been observed.
Research has shown that green crab have the potential to outcompete native Dungeness crab of approximately equal size for food and habitat. Smaller native shore crabs, such as yellow shore crabs (Hemigrapsus oregonensis) are heavily preyed upon by voracious green crab. Juvenile Pacific oysters, a species important in the mariculture industry in Alaska, are a favored prey species. Oyster farmers on the east coast have had to alter the gear in which they grow out young oysters to deter predation by green crab.