BIOTIC Species Information for Carcinus maenas
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Researched byKen Neal & Paolo Pizzolla Data supplied byMarLIN
Refereed byThis information is not refereed.
General Biology
Growth formArticulate
Feeding methodOmnivore
Mobility/MovementCrawler
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
SociabilitySolitary
Toxic/Poisonous?No
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).

Growth
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.

Diet
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).

Parasites
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,
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