Carcinus maenas
Carcinus maenas
(green crab)
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Carcinus maenas Linnaeus 1758

Common name: green crab

Synonyms and Other Names: Cancer marinus sulcatus Rumph, 1705; Cancer maenas Linnaeus, 1758; Portunus maenas Leach, 1814; Carcinus maenas Leach, 1814

Taxonomy: available through www.itis.govITIS logo

Identification: Description taken from Rathbun (1930).  The carapace is finely granular, about as long as broad with 5 acuminate antero-lateral teeth.  Antero-lateral teeth tipped with yellow.  Frontal area between orbits with three rounded teeth.  Carapace color variable, usually mottled, dark brown to dark green, granules for the most part yellow.  Female ground color orange in place of green with whitish granules. Claws similar with small black spots arranged longitudinally on palm.  Fingers and adjacent portion of palm light blue with black stripes in grooves.  Walking legs green, speckled with black.  Second and third pair of walking legs longest and about 1and 2/3 times the length of the carapace; fourth pair of legs shorter than the first.  Last pair of legs somewhat flattened and with setae.  McKnight et al. (2000) noted that the color of the ventral surface and limbs of the crab may vary from green to yellow, orange and red with physiological and ecological differences observed based on color phase (see below).  Adult green crabs range in size from 6 to 10 cm in carapace width (Washington Department of Fish and Wildlife 2001).

Size: From 6 to 10 cm in carapace width

Native Range: The green crab's native range extends along the Atlantic coasts of Europe and northern Africa from Norway and the British Isles south to Mauritania (Washington Department of Fish and Wildlife 2001).

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Nonindigenous Occurrences: Coastal areas from Maine to Virginia. Earliest documentation in North America from 1817 on the East Coast. First collected on the West Coast in San Francisco Bay in 1989.

The green crab is now dispersed globally with records of occurrence in Australia, Hawaii, Sri Lanka, South Africa, along the Atlantic and Pacific coasts of North America, and the Atlantic coast of South America (Introduced Marine Aquatic Invaders, Fisheries of Western Australia).  Carcinus maenas was introduced to the Atlantic coast of North America by the year 1817 (Say 1817) and its range now extends from Nova Scotia (Cameron 2003) to Virginia (Kingsley 1879).  Rathbun (1930) listed U. S. National Museum records for this species as follows: Maine - Casco Bay, 1911.  Massachusetts - Ipswich, 1903; Vineyard Sound, 1875; Woods Hole, 1882, 1883, 1885,1887,1888, 1892; Naushon Island, 1882.  Rhode Island - Newport, 1880. New York - Long Island Sound, 1874; Fire Island, 1884; New Jersey - Longport, 1929; Cape May Point, 1929. Other Atlantic coast records include: coastal waters of Maryland (Maryland Sea Grant 1996), Chincoteague Bay, Virginia (regularly encountered according to Hines 1996, unpublished data), and Penobscot and Passamaquoddy bays in Maine (Fofonoff et al. 2003).  The crab is established in Chesapeake Bay, Maryland (Ruiz 2000).  The green crab is not common in Delaware waters and has not been collected from the Chesapeake Bay proper (Fofonoff et al. 2003).  First occurrence of the species on the Pacific coast of the U.S. was in 1989 in the Estero Americano estuary, California (Cohen and Carlton 1995).  It has since expanded its range as far south as Morro Bay, California near San Luis Obispo (Grosholz, personal communication) and as far north as Lemmens Inlet near Tofino, Vancouver Island, British Columbia (Yamada as cited in Holmes 2001).  Established in Willapa Bay, Washington (Washington Dept. of Fish and Wildlife 2001).

Ecology: Carcinus maenas has colonized all types of protected and semi-protected marine and estuarine habitats, including habitats with mud, sand, or rock substrates, submerged aquatic vegetation, and emergent marsh (Cohen and Carlton 1995).  Dumbauld (as cited in Holmes 2001) noted that the presence of green crabs in Washington's Willapa Bay was highly correlated with the occurrence of Spartina alterniflora, another invasive species.  Green crabs are ecologically important in rocky intertidal communities in eastern North America (Menge 1995); however, they have not occupied exposed rocky shores in western North America (Grosholz and Ruiz 2002).  Postlarval crabs are found in intertidal areas and in the subtidal zone as deep as 55m (Grosholz and Ruiz 2002).  Reviewing studies from countries with established populations of the green crab, Grosholz and Ruiz (2002) noted that within its present range, C. maenas is often the most abundant crab species in soft-sediment bays and estuaries of Europe, Australia, and both coasts of North America.  Green crabs are both euryhaline, tolerating salinities from 4 to 52 ppt, and eurythermic, surviving in temperatures from 0 to 30C (Cohen and Carlton 1995).  The larvae are less tolerant of temperature and salinity extremes with successful development occurring at temperatures between 11 and 25C and salinities between 26 and 39 ppt (Washington Department of Fish and Wildlife 2001).  First stage zoeae are transported offshore with development to the megalopal stage occurring in ~ two weeks.  Reinvasion of nearshore waters occurs during the megalopal stage with molt to the first crab stage taking place in the upper intertidal zone (Washington Department of Fish and Wildlife).  Females may produce up to 185,000 eggs per sponge (Cohen and Carlton 1995).  Prey items include clams, mussels, oysters, and gastropods.

Means of Introduction: This species has the ability to disperse as adults by a variety of anthropogenic and natural mechanisms including: 1) ballast, 2) ship's hulls, 3) packing materials (seaweeds) used to ship live marine organisms, 4) bivalves moved for aquaculture, 5) rafting, 6) migration on surface currents, and 7) movement of submerged aquatic vegetation for coastal zone management initiatives (Introduced Marine Aquatic Invaders, Fisheries of Western Australia).  Green crabs also spread by planktonic transport of larvae and once established in an area can expand their range rapidly (Grosholz 1996, Grosholz and Ruiz 2002).  Research data strongly suggest that colonization of estuaries in Washington, Oregon and British Columbia was facilitated by the El Nino events of 1997 and 1998 (Washington Department of Fish and Wildlife 2001).  Holmes (2001) also noted that the vector of introduction to Washington State was probably "simple larval transport" from established populations in California and Oregon.

Status: According to Grosholz and Ruiz (2002), the green crab is one of the most successful invasive predators in coastal ecosystems with populations established on five continents.  They noted that these crabs were able to expand their range over 750 km in less than ten years on the Pacific coast of North America with populations firmly established in every significant bay and estuary from Monterey Bay, California to Gray's Harbor, Washington. Because of their ability to rapidly expand their range, Cohen et al. (1995) suggested that the species has the potential to spread and become established from Alaska to Baja California.  Expansion of the range on the east coast of North America has been primarily northward.

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.

Remarks: McKnight et al. (2000) studied the distribution of color forms of the green crab along the southern New England coast and found that color phase in introduced populations was similar to that of native populations in Europe.  They found that red and green phase crabs were differentially distributed among three coastal habitats (open shore intertidal, open shore subtidal, and estuarine) with distribution controlled by decreased physiological tolerance in red phase forms.  McGaw et al. (1992) noted that red phase crabs were larger and suggested that red coloration only develops in large crabs as a result of an extended intermolt or a terminal anecdysis.

References: (click for full references)

Cameron, B. 2003. Recruitment of the invasive green crab, Carcinus maenas, in Nova Scotia.  Master's Thesis, Dalhousie University, Halifax, Nova Scotia, Canada.

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.

Fofonoff, P.W., Ruiz, G. M., Steves, B., Hines, A.H.; Carlton, J. T. 2003. National Exotic Marine and Estuarine Species Information System: Chesapeake Bay Introduced Species Database:

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.

Kingsley, J.S. 1879. On a collection of Crustacea from Virginia, North Carolina, and Florida, with a revision of the genera of Crangonidae and Palaemonidae. Proceedings of the Academy of Natural Sciences of Philadelphia 31: 383-427

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.

McGaw, I.J., M.J. Kaiser, E. Naylor, and R.N. Hughes. 1992. Intraspecific morphological variation related to the moult-cycle and colour phase of the shore crab Carcinus maenas. Journal Zoological Society, London 228:351-359.

McKnight, A., L.M. Mathews, R. Avery, and K.T. Lee. 2000. Distribution is correlated with color phase in green crabs, Carcinus maenas (Linnaeus, 1758) in southern New England.  Crustaceana 73(6):643-770.

Menge, B.A. 1995. Indirect effects in marine rocky intertidal interaction webs: patterns and importance.  Ecological Monographs 65:12-74.

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.

Rathbun, M. J. 1930. The cancroid crabs of America of the families Euryalidae, Portunidae, Atelecyclidae, Cancridae, and Xanthidae. U.S. Natl. Mus. Bull. 152:1-609.

Say, T. 1817. An account of the Crustacea of the United States.  Journal Academy Natural Sciences Philadelphia 1: 57-63.

Tettlebach, S.T. 1986. Dynamics of crustacean predation on the northern bay scallop, Argopecten irradians irradians.  Ph.D. Dissertation, University of Connecticut.

Washington Department of Fish and Wildlife. 2001. Aquatic Nuisance Species, European Green Crab.

Other Resources:
Carcinus maenus (green crab) (WA Dept. Fish & Wildlife)

Carcinus maenus [green crab] (ANS Clearinghouse Bibliography)

Carcinus maenas (Global Invasive Species Database)

European shore crab (Carcinus maenas) (Introduced Marine Aquatic Invaders, Fishes of Western Australia)

Author: Harriet Perry

Revision Date: 9/13/2011

Citation Information:
Harriet Perry. 2017. Carcinus maenas. USGS Nonindigenous Aquatic Species Database, Gainesville, FL. Revision Date: 9/13/2011

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.

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Citation information: U.S. Geological Survey. [2017]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [3/30/2017].

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