BIOTIC Species Information for Carcinus maenas
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Researched byKen Neal & Paolo Pizzolla Data supplied byMarLIN
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Scientific nameCarcinus maenas Common nameCommon shore crab
MCS CodeS1594 Recent SynonymsNone

PhylumCrustacea Subphylum
Superclass ClassEumalacostraca
SubclassEucarida OrderDecapoda
SuborderPleocyemata FamilyCancridae
GenusCarcinus Speciesmaenas

Additional InformationNo text entered
Taxonomy References Hayward et al., 1996, Hayward & Ryland, 1995b, Fish & Fish, 1996, Howson & Picton, 1997,
General Biology
Growth formArticulate
Feeding methodOmnivore
Environmental positionEpibenthic
Typical food typesAny animal or plant material (see additional information). HabitFree living
Bioturbator FlexibilityNone (< 10 degrees)
FragilityFragile SizeSmall-medium(3-10cm)
HeightInsufficient information Growth RateSee additional information
Adult dispersal potential1km-10km DependencyIndependent
General Biology Additional InformationGeneral
Carcinus maenas is an easily identifiable crab of estuaries, sheltered rocky shores and offshore waters (Crothers, 1968). With increasing exposure on rocky shores, Carcinus maenas is replaced by other crab species such as the velvet swimming crab Necora puber, the bristly crab Pilumnus hirtellus, the edible crab Cancer pagurus and Montagu's crab Xantho incisus, and on increasingly exposed sandy areas by Pennant's swimming crab Portumnus latipes, the masked crab Corystes cassivelaunus, the harbour crab Liocarcinus depurator and the flying crab, Liocarcinus holsatus (Crothers, 1968).

Some large Carcinus maenas have red limbs and undersides rather than the usual green. This is thought to be related to the breeding period (Ditmmann & Villbrandt, 1999) and prolonged intermoult, and is caused by photodegradation of the green exoskeletal pigment. Red morphs of Carcinus maenas were found to have a thicker carapace for greater protection during intraspecific conflict for mates. However, the red morph was also found to have a higher metabolic demand and were less tolerant to changes in salinity and temperature compared to the green morph (Dittmann & Villbrandt, 1999). Green Carcinus maenas are mainly found sheltering under algae where their colour blends-in with the background. Red Carcinus maenas appear brown against a brown background in deep water and are mostly found in the shallow sublittoral where red light does not penetrate. Juvenile Carcinus maenas often have white patches on the carapace to breakup their outline against shell and gravel (Crothers, 1968). In the Wadden Sea and, probably colder, northern parts of Britain, Carcinus maenas migrates to subtidal areas and remains there until spring. During this time the crabs are inactive in shelters and do not feed (Dittmann & Villbrandt, 1999). Lack of prey in the winter also leads to starvation and inactivity (Scott-Fordsmand & Depledge, 1993).

Carcinus maenas increases its body size by 20-33% per moult (Klein Breteler, 1975) and takes about 10 moults to reach 20 mm carapace width (CW) in its first year, if conditions are favourable (Crothers,1967). Carcinus maenas may moult more than once per year after the first year if conditions are good but moulting rate slows once maturity is reached (Crothers, 1967) and is probably about once per year post maturity.

Carcinus maenas can be considered a true omnivore and consumes plants, algae, molluscs, arthropods (including their own species), annelids and carrion. Animal matter makes up the majority of the diet but some plant matter including algae and cord grass Spartina sp. is consumed. The diet of large Carcinus maenas mainly consists of molluscs and the common mussel Mytilus edulis is the most important of these. Smaller crabs (<30 mm CW) have more plant matter and arthropods in their diet. On rocky shores, juvenile Carcinus maenas were found to consume the barnacle Semibalanus balanoides whereas adults consume more gastropods (Rangley & Thomas, 1987) especially the dogwhelk Nucella lapillus and winkles Littorina sp. (Little & Kitching, 1996). Semibalanus balanoides is abundant and supports rapid growth (frequent moulting) in the early life stages of Carcinus maenas (Rangley & Thomas, 1987). Peak foraging occurs at night around high tide (Ropes, 1969). Predation rate is dependent on prey density (Walton et al., 2002) and temperature (Sanchez-Salazar et al., 1987).

The most well known parasite of Carcinus maenas is the rhizocephalan barnacle Sacculina carcini. This parasite infects by larval settlement on the exoskeleton and subsequent infection into the haemocoel by injection through a chitin 'needle' at the base of a hair on one of the legs of the host. Any larvae that do not settle adjacent a hair base do not survive (Smith, 1907). Sacculina carcini castrates male and female Carcinus maenas and prevents moulting for the rest of the crabs life (Naylor, 2000; Thresher et al., 2000 and references therein). Infected crabs with sexually mature parasites carry a reproductive externae in the same way as females carry an egg-mass when they are berried. The externae is distinguishable from an egg-mass because it is smooth rather than granular (Naylor, 2000).

Carcinus maenas is the 1st host of the acanthocephalan helminth Profilicollis botulus which infects eider ducks (Somateria mollissima) by ingestion of infected crabs. Juvenile eider ducks suffer some mortality from heavy infections and crabs are infected by eggs of the parasite from duck faeces(Thompson, 1985).

Small Carcinus maenas (3-11 mm CW) can be attacked by the parasitoid platyhelminth Fecampia erythrocephala. This parasitoid is 8-12 mm long and replaces much of the digestive gland in the haemocoel. Infection is usually 1 worm per crab but may be as many as 4. Once the worm is mature it exits the crab, killing it in the process. Prevalence in natural populations is about 7% and Kuris et al., (2002) suggested Fecampia erythrocephala may be a useful biocontrol where introduced Carcinus maenas are a pest because it kills crabs before they can mature and breed.
Biology References Crothers, 1968, Dittmann & Villbrandt, 1999, Scott-Fordsman & Depledge, 1993, Klein Breteler, 1975, Crothers, 1967, Ropes, 1969, Walton et al., 2002, Sanchez-Salazar et al. 1987b, Smith, 1907, Naylor, 2000, Thresher et al., 2000, Kuris et al., 2002, Little & Kitching, 1996,
Distribution and Habitat
Distribution in Britain & IrelandThis ubiquitous crab is found on all shores of Britain and Ireland.
Global distributionNorth Eastern Atlantic from northern Norway southwards to West Africa. It has been introduced to the USA, Sri Lanka, Red Sea, Madagascar, South Africa and Australia.
Biogeographic rangeNot researched Depth rangeIntertidal down to 60 m.
MigratoryInsufficient information   
Distribution Additional InformationNo text entered

Substratum preferencesNo preference
Physiographic preferencesOpen coast
Strait / sound
Ria / Voe
Isolated saline water (Lagoon)
Enclosed coast / Embayment
Biological zoneUpper Eulittoral
Mid Eulittoral
Lower Eulittoral
Sublittoral Fringe
Upper Infralittoral
Lower Infralittoral
Upper Circalittoral
Lower Circalittoral
Wave exposureSheltered
Very Sheltered
Extremely Sheltered
Ultra Sheltered
Tidal stream strength/Water flowModerately Strong (1-3 kn)
Weak (<1 kn)
Very Weak (negligible)
SalinityLow (<18 psu)
Variable (18-40 psu)
Full (30-40 psu)
Reduced (18-30 psu)
Habitat Preferences Additional Information
Distribution References Hayward et al., 1996, Hayward & Ryland, 1995b, Fish & Fish, 1996, NBN, 2002, JNCC, 1999, Picton & Costello, 1998, Ameyaw-Akumfi & Naylor, 1987,
Reproduction/Life History
Reproductive typeGonochoristic
Developmental mechanismPlanktotrophic
Reproductive SeasonSee additional information Reproductive LocationAs adult
Reproductive frequencyAnnual protracted Regeneration potential No
Life span6-10 years Age at reproductive maturity1-2 years
Generation time1-2 years FecundityInsufficient information
Egg/propagule sizeUp to 185,000 eggs. Fertilization typeInternal
Larval/Juvenile dispersal potential>10km Larval settlement periodInsufficient information
Duration of larval stage1-2 months   
Reproduction Preferences Additional InformationDuration of reproductive season is related to geographical location. Egg-bearing females can be found year-round in the south of England, between January and April/May in the Bristol Channel and Wash area and only in spring in northern Scotland (Ingle, 1980). In areas where there is a defined reproductive season, females aggregate at 'hotspots' and males compete for copulatory opportunities (van der Meeren, 1994). Males preferentially select females with a carapace width 10 mm smaller than their own but are not size selective below this threshold and do not select females on the basis of imminence of moult (Reid et al., 1994). Males 65 mm carapace width or more are large enough to dominate competitive interactions and often mate with several females. However, males of this size only make up approximately 5% of the population (van der Meeren, 1994). Unmated males will try to displace males in precopula (a male carrying a female beneath its body held by one of the legs, prior to the female moulting) and always loses out to a male that has a carapace width 9 mm or larger than its own. Males that are similar size are likely to win intrasex conflicts 50% of the time (Reid et al., 1994).
After moulting the 'soft' female is turned over by the male and copulation ensues through modified pleopods on the much reduced abdomen. As with most crabs, the female bears the fertilized eggs in a mass held between the abdomen and underside of the carapace. Females are berried for up to 4 months, depending on temperature, before the eggs hatch in spring/summer. Females in estuaries migrate to the mouth of the estuary to release larvae at night on ebb tides into fully saline water (Queiroga, 1996). At the southern limit of its range, larvae are released in winter when water temperatures are cooler (Sprung, 2001). Carcinus maenas was reported to breed only at temperatures below 18°C (Crothers, 1967). The maximum fecundity recorded was 185,000 eggs (Crothers, 1967).
Reproduction References Queiroga, 1996, Crothers, 1967, Ingle, 1980, Meeren van der, 1994, Reid et al., 1994, Sprung, 2001,
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