page_title: Carcinus maenas
section_title: Ecology
hierarchical_section_title: Carcinus maenas / Ecology
caption_attribution_description: Argopecten irradiansEnglish: A live individual of Argopecten irradians, the Atlantic Bay scallop, photographed at the Marine Biological Laboratory in Woods Hole
context_page_description: Carcinus maenas is a common littoral crab. It is known by different names around the world. In the British Isles, it is generally referred to as the shore crab, or green shore crab. In North America and South Africa, it bears the name green crab or European green crab. In Australia and New Zealand, it is referred to as either the European green crab or European shore crab.
  C. maenas is a widespread invasive species, listed among the 100 "world's worst alien invasive species". It is native to the north-east Atlantic Ocean and Baltic Sea, but has colonised similar habitats in Australia, South Africa, South America and both Atlantic and Pacific coasts of North America. It grows to a carapace width of 90 mm, and feeds on a variety of mollusks, worms, and small crustaceans, potentially affecting a number of fisheries. Its successful dispersal has occurred by a variety of mechanisms, such as on ships' hulls, sea planes, packing materials, and bivalves moved for aquaculture.
context_section_description: C. maenas can live in all types of protected and semiprotected marine and estuarine habitats, including those with mud, sand, or rock substrates, submerged aquatic vegetation, and emergent marsh, although soft bottoms are preferred. C. maenas is euryhaline, meaning that it can tolerate a wide range of salinities (from 4 to 52 ‰), and survive in temperatures of 0 to 30 °C (32 to 86 °F). The wide salinity range allows C. maenas to survive in the lower salinities found in estuaries, and the wide temperature range allows it to survive in extremely cold climates beneath the ice in winter. A molecular biological study using the COI gene found genetic differentiation between the North Sea and the Bay of Biscay, and even more strongly between the populations in Iceland and the Faroe Islands and those elsewhere. This suggests that C. maenas is unable to cross deeper water.
  Females can produce up to 185,000 eggs, and larvae develop offshore in several stages before their final moult to juvenile crabs in the intertidal zone. Young crabs live among seaweeds and seagrasses, such as Posidonia oceanica, until they reach adulthood.
  C. maenas has the ability to disperse by a variety of mechanisms, including ballast water, ships' hulls, packing materials (seaweeds) used to ship live marine organisms, bivalves moved for aquaculture, rafting, migration of crab larvae on ocean currents, and the movement of submerged aquatic vegetation for coastal zone management initiatives.  C. maenas dispersed in Australia mainly by rare long-distance events, possibly caused by human actions.
  C. maenas is a predator, feeding on many organisms, particularly bivalve molluscs (such as clams, oysters, and mussels), polychaetes, and small crustaceans. They are primarily diurnal, although activity also depends on the tide, and crabs can be active at any time of day. In California, preferential predation of C. maenas on native clams (Nutricola spp.) resulted in the decline of the native clams and an increase of a previously introduced clam (the amethyst gem clam, Gemma gemma), although it C. maenas also voraciously preys on introduced clams such as Potamocorbula amurensis. The soft-shell clam (Mya arenaria) is a preferred prey species of C. maenas. Consequently, it has been implicated in the destruction of the soft-shell clam fisheries on the east coast of the United States and Canada, and the reduction of populations of other commercially important bivalves (such as scallops, Argopecten irradians, and northern quahogs, Mercenaria mercenaria). The prey of C. maenas includes the young of bivalves and fish, although the effect of its predation on winter flounder, Pseudopleuronectes americanus is minimal. C. maenas can, however, have substantial negative impacts on local commercial and recreational fisheries, by preying on the young of species, such as oysters and the Dungeness crab, or competing with them for resources. Colder water temperatures reduce overall feeding rates of C. maenas.
  To protect itself against predators, C. maenas uses different camouflage strategies depending on their habitat: crabs in mudflats try to resemble their surroundings with colours similar to the mud while crabs in rock pool use disruptive coloration.
caption: Argopecten irradians, a scallop which has been affected by the introduction of C. maenas
exif: {"Image Make": "PENTAX Corporation", "Image Model": "PENTAX Optio WPi", "Image XResolution": "72", "Image YResolution": "72", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Optio WPi Ver 1.00", "Image DateTime": "2007:05:24 10:25:49", "Image ExifOffset": "201", "EXIF ExposureTime": "1/40", "EXIF FNumber": "33/5", "EXIF ISOSpeedRatings": "80", "EXIF ExifVersion": "0220", "EXIF DateTimeOriginal": "2007:05:24 10:25:49", "EXIF DateTimeDigitized": "2007:05:24 10:25:49", "EXIF CompressedBitsPerPixel": "2", "EXIF ExposureBiasValue": "0", "EXIF MaxApertureValue": "17/5", "EXIF MeteringMode": "Pattern", "EXIF Flash": "Flash fired, compulsory flash mode", "EXIF FocalLength": "63/10", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "720", "EXIF ExifImageLength": "389", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Auto", "EXIF DigitalZoomRatio": "1", "EXIF FocalLengthIn35mmFilm": "38", "EXIF SceneCaptureType": "Standard", "EXIF Contrast": "Normal", "EXIF Saturation": "Normal", "EXIF Sharpness": "Normal", "EXIF SubjectDistanceRange": "2"}