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Carcinus maenas

2007 Schools Wikipedia Selection. Related subjects: Organisms

               iCarcinus maenas
           Scientific classification

   Kingdom:    Animalia
   Phylum:     Arthropoda
   Subphylum:  Crustacea
   Class:      Malacostraca
   Order:      Decapoda
   Suborder:   Pleocyemata
   Infraorder: Brachyura
   Family:     Portunidae
   Genus:      Carcinus
   Species:    C. maenas

                                Binomial name

   Carcinus maenas
   (Linnaeus, 1758)

   Carcinus maenas is a common littoral crab, and an important invasive
   species. It is listed among the 100 "world's worst invasive alien
   species" .

   C. maenas is known by different names around the world. In the British
   Isles, it is generally referred to simply as the 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.

Description

   C. maenas has a carapace up to 60  mm long, with five short teeth along
   the rim behind each eye, and three undulations between the eyes. The
   undulations, which do not protrude beyond the eyes are the simplest
   means of distinguishing C. maenas from the closely-related C.
   aestuarii, which can also be an invasive species. In C. aestuarii, the
   carapace lacks any bumps and extends forward beyond the eyes. The other
   character for distinguishing the two species is the form of the first
   and second pleopods (collectively the gonopods), which are straight and
   parallel in C. aestuarii, but curve outwards in C. maenas .

   The colour of C. maenas varies greatly, from green to brown, grey or
   red. This variation has a genetic component but is largely due to local
   environmental factors . In particular, individuals which delay moulting
   become red–coloured rather than green. Red individuals are stronger and
   more aggressive, but are less tolerant of environmental stresses, such
   as low salinity or hypoxia .

Native and introduced range

   Rough map of the distribution of Carcinus maenas. Blue areas are the
   native range; red areas are the introduced or invasive range. Black
   dots represent single sightings that did not lead to invasion, and
   green areas are the potential range of the species.
   Enlarge
   Rough map of the distribution of Carcinus maenas. Blue areas are the
   native range; red areas are the introduced or invasive range. Black
   dots represent single sightings that did not lead to invasion, and
   green areas are the potential range of the species.

   C. maenas is native to European and North African coasts as far as the
   Baltic Sea in the east, and Iceland and central Norway in the north,
   and is one of the commonest crabs throughout much of its range. In the
   Mediterranean Sea, it is replaced by the closely-related species
   Carcinus aestuarii.

   C. maenas was first observed on the east coast of North America in
   Massachusetts in 1817, and may now be found from Nova Scotia to
   Virginia.

   In Australia, C. maenas was first reported in the late 19th century, in
   Port Phillip Bay, Victoria. It has since spread along the coast of
   Victoria, reaching New South Wales in 1971, South Australia in 1976 and
   Tasmania in 1993. One specimen was found in Western Australia in 1965,
   but C. maenas has not been seen in the area since .

   C. maenas first reached South Africa in 1983, in the Table Docks area
   near Cape Town . Since then, it has spread at least as far as Saldanha
   Bay in the north and Camps Bay in the south, over 100  km apart.

   In 1989, C. maenas was found in San Francisco Bay, California, on the
   Pacific coast of the United States. Until 1993, it was not able to
   extend its range, but reached Oregon in 1997, the state of Washington
   in 1998 and British Columbia in 1999 .

   In 2003, C. maenas was discovered in Patagonia .

   Other appearances that have not, however, led to invasions have been
   recorded in Brazil, Panama, Hawaii, Madagascar, the Red Sea, Pakistan,
   Sri Lanka and Myanmar; Japan has been invaded by a related crab, either
   C. aestuarii or a hybrid of C. aestuarii and C. maenas .

   It is believed, based on the ecological conditions, that C. maenas
   could eventually extend its range to colonise the Pacific coast of
   North America from Baja California to Alaska . Similar ecological
   conditions are to be found on many of the world's coasts, with the only
   large potential area not to have been invaded yet being New Zealand;
   the New Zealand government has taken action, including the release of a
   Marine Pest Guide in an effort to prevent colonisation by C. maenas.

Ecology

   A young Carcinus maenas showing the common green colour
   Enlarge
   A young Carcinus maenas showing the common green colour

   C. maenas can live in 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, 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 from 0 °C to 30°C . The wide salinity range allows C.
   maenas to survive in the lower salinities found in estuaries.

   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 in Posidonia oceanica meadows until
   they reach adulthood .

   C. maenas is a predator and feeds on many organisms, particularly
   bivalve molluscs (such as clams, oysters, and mussels), polychaetes and
   small crustaceans . They are primarily nocturnal, although activity
   also depends on the tide, and crabs can be active at any time of day .

   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. Thresher et al. found that in Australia C. maenas
   dispersed mainly by rare long-distance events, possibly caused by human
   actions.

   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) . C. maenas has been implicated in the destruction of the
   soft-shell clam (Mya arenaria) 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 .

Control

   Due to its potentially harmful effects on ecosystems, various efforts
   have been made to control introduced populations of C. maenas around
   the world. In Edgartown, Massachusetts, a bounty was levied in 1995 for
   catching C. maenas, in order to protect local shellfish, and 10  tonnes
   were caught .

   There is evidence that the native blue crab in eastern North America,
   Callinectes sapidus, is able to control populations of C. maenas;
   numbers of the two species are negatively correlated, and C. maenas is
   not found in Chesapeake Bay, where Callinectes sapidus is most frequent
   . On the west coast of North America, C. maenas appears to be limited
   to upper estuarine habitats in part by predation by native rock crabs
   (Cancer antennarius and Cancer productus) and competition for shelter
   with a native shore crab, Hemigrapsus oregonensis . Host specificity
   testing has recently been conducted on Sacculina carcini, a parasitic
   barnacle, as a potential biological control agent of C. maenas . In the
   laboratory, Sacculina settled on, infected, and killed native
   California crabs, including the Dungeness crab, Cancer magister, and
   the shore crabs Hemigrapsus nudus, Hemigrapsus oregonensis and
   Pachygrapsus crassipes. Dungeness crabs were the most vulnerable of the
   tested native species to settlement and infection by the parasite.
   Although Sacculina did not mature in any of the native crabs,
   developing reproductive sacs were observed inside a few Cancer magister
   and Hemigrapsus oregonensis. Any potential benefits of using Sacculina
   to control C. maenas on the west coast of North America would need to
   be weighed against these potential non-target impacts .

   C. maenas has also caused significant problems in the Republic of
   Ireland where predation of bottom-cultured mussels has been recorded in
   several counties ( Kerry, Wexford, Waterford), and a number of control
   programmes have been instigated by mussel producers. "Hard-eye" shrimp
   creels are typically used to fish C. maenas in Ireland; the creels are
   baited, deployed and fished in 24-hour cycles, being typically deployed
   in strings along the boundaries of mussel beds in order to lure the
   crabs out of the mussel beds. Some producers pay levies for the removal
   of crabs, but in most cases, C. maenas catches are sold for processing
   into food products. This is, however, a small market and the relatively
   low value of C. maenas (€500 per tonne) and high transport costs
   (refrigerated lorry €170 per tonne) means that fishing C. maenas is
   uneconomical unless it forms part of a control programme to protect
   more valuable shellfish beds.

Fishery

   C. maenas is fished on a small scale in the north-east Atlantic Ocean,
   with approximately 1200  tonnes being caught annually, mostly in France
   and the United Kingdom. In the north-west Atlantic, C. maenas was the
   subject of fishery in the 1960s, and again since 1996, with up to
   86 tonnes being caught annually .
   Retrieved from " http://en.wikipedia.org/wiki/Carcinus_maenas"
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