Impact of Introduction: Introductions had a negative impact on soft-shell clams, young oysters, and native crabs in the Northeast beginning in the 1950s.
Significant impacts to commercial fisheries and natural ecosystems have been documented. Green crabs have been implicated in the destruction of the soft-shell clam (Mya arenaria) fisheries in New England (Cohen and Carlton 1995) and the reduction of populations of other commercially important bivalves including the scallop, Argopecten irradians, and the northern quahog, Mercenaria mercenaria (Morgan et al. 1980; Walton, unpublished data as cited in Grosholz and Ruiz 2002). In Connecticut, weekly rates of crab predation on scallops were as high as 70% leading Tettlebach (1986) to observe that green crabs were responsible for most observed mortality in scallops and were a limiting factor in population size. MacPhail et al. (1955) concluded that the green crab was "one of the worst, if not the worst, clam predators we know."
Green crabs readily prey on Dungeness crabs of equal or lesser size and because the two species co-occur in intertidal areas, green crabs may reduce recruitment through predation on small juveniles in the fishery for Cancer magister (Grosholz and Ruiz 2002). Lafferty and Kuris (1996) estimated commercial fishery losses in the United States resulting from green crab predation at $44 million dollars. Green crabs eat a wide variety of prey organisms and can significantly reduce populations of native clams and crabs in areas where they have become established. Their ability to out compete native species for food resources, high reproductive capacity, and wide environmental tolerances lend them the capacity to fundamentally alter community structure in coastal ecosystems.
References: (click for full references)
Cameron, B. 2003. Recruitment of the invasive green crab, Carcinus maenas
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Cohen, A.N. and J.T. Carlton. 1995. Nonindigenous Aquatic Species in a United States Estuary: A Case Study of the Biological Invasions of the San Francisco Bay and Delta. Report to the U.S. Fish and Wildlife Service and the National Sea Grant College Program, Connecticut. 262 pp.
Cohen, A.N., J.T. Carlton, and M. Fountain. 1995. Introduction, dispersal, and potential impacts of the green crab Carcinus maenas in San Francisco Bay, California. Marine Biology 122:225-237.
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Grosholz, E. and G. Ruiz (editors). 2002. Management Plan for the European Green Crab. Aquatic Nuisance Species Task Force. 55 pp.
Grosholz, E.D. 1996. Contrasting rates of spread for introduced species in terrestrial and marine systems. Ecology 77:1680-1686.
Holmes, D. 2001. The green crab invasion: a global perspective, with lessons from Washington State. Master's Thesis, Evergreen State College, Olympia, Washington.
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Lafferty, K.D. and A.M. Kuris. 1996. Biological control of marine pests. Ecology 77:1989-2000.
MacPhail, J.S., E.I. Lord, and L.M. Dickie. 1955. The green crab-a new clam enemy. Fisheries Research Board Canada, Progress Report 1:1-16.
Maryland Sea Grant. 1996. An endless invasion? Green crabs, New England invaders, move west. Maryland Sea Grant, Maryland Marine Notes 14(2):1-5.
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Morgan, D.E., J. Goodsell, G.C. Mathiessen, J. Garey, and P. Jacobson. 1980. Release of hatchery-reared bay scallops (Argopecten irradians) onto a shallow coastal bottom in Waterford, Connecticut. Proceedings World Mariculture Society 11:247-261.
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This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.