Cancer pagurus, commonly known as the edible crab or brown crab, is a species of crab found in the North Sea, North Atlantic Ocean and perhaps in the Mediterranean Sea. It is a robust crab of a reddish-brown colour, having an oval carapace with a characteristic "pie crust" edge and black tips to the claws. A mature adult may have a carapace width of up to 25 cm (10 in) and weigh up to 3 kg (6.6 lb). C. pagurus is a nocturnal predator, targeting a range of molluscs and crustaceans. It is the subject of the largest crab fishery in Western Europe, centred around the coasts of the British Isles, with more than 60,000 tonnes caught annually.
The carapace of C. pagurus adults is a reddish-brown colour, while in young specimens it is purple-brown. It occasionally bears white patches, and is marked along the front edge with nine rounded lobes, resembling a pie crust. Males typically have a carapace 60 millimetres (2.4 in) long, and females 98 mm (4 in) long, although they may reach up to 150 mm (6 in) long in exceptional cases. Carapace width is typically 150 mm (6 in), or exceptionally up to 250 mm (10 in). A fold of the carapace extends ventrally to constitute a branchial chamber where the gills lie.
The first pereiopod is modified into a strong cheliped (claw-bearing leg): the claw's fingers, the dactylus and propodus, are black at the tips. The other pereiopods are covered with rows of short stiff setae and the dactylus is black at the tip, and ends in a sharp tip.
From the front, the antennae and antennules are visible. Beside these there are the orbits in which the eyes are situated. The mouthparts comprise three pairs of maxillipeds, behind which there are a pair of maxillae, a pair of maxillules, and finally the mandibles.
Reproduction occurs in winter; the male captures the female and holds her under himself until she moults. Internal fertilisation takes place before the hardening of the new carapace, with the aid of two abdominal appendages (gonopods). After mating, the female retreats to a pit on the sea floor to lay her eggs. Between 250,000 and 3,000,000 fertilised eggs are held under the female's abdomen for up to eight months until they hatch.
The first developmental stage after hatching is a planktonic larva (1 mm) called the zoea that develops into a postlarva (megalopa), and finally a juvenile. The first juvenile stage is characterised by a well developed abdomen, which will, in time, become reduced in size and folded under the sternum. Juveniles settle to the sea floor in the intertidal zone, where they stay until they reach a carapace width of 60–70 mm (2.4–2.8 in) and then migrate to deeper water. The growth rate in males slows from an increase in carapace width of 10 mm per year before it is eight years old, to 2 mm per year thereafter. Females grow at about half the rate of males, probably due to the energetic demands of egg laying. Sexual maturity is reached at a carapace width of 12.7 cm (5.0 in) in females, and 11 cm (4.3 in) in males. Longevity is typically 25–30 years, although exceptional individuals may live for up to 100 years.
Distribution and ecology
Cancer pagurus is abundant throughout the northeast Atlantic as far as Norway in the north and northern Africa in the south, on mixed coarse grounds, mud and sand from shallow sublittoral to about 100 metres (330 ft). Unconfirmed reports suggest that C. pagurus may also occur in the Mediterranean Sea and Black Sea. It is frequently found inhabiting cracks and holes in rocks but occasionally also in open areas. Smaller specimens may be found under rocks in the littoral zone.
Adult C. pagurus are nocturnal, hiding buried in the substrate during the day, but foraging up to 50 metres (160 ft) from their hideouts at night. Their diet includes a variety of crustaceans (including the crabs Carcinus maenas and Pilumnus hirtellus, the porcelain crabs Porcellana platycheles and Pisidia longicornis, and the squat lobster Galathea squamifera) and molluscs (including the gastropods Nucella lapillus and Littorina littorea, and the bivalves Ensis, Mytilus edulis, Cerastoderma edule, Ostrea edulis and Lutraria lutraria). It may stalk or ambush motile prey, and may dig large pits to reach buried molluscs. The main predator of Cancer pagurus is the octopus, which will even attack them inside the crab pots that fishermen use to trap them.
Compared to other commercially important crab species, relatively little is known about diseases of Cancer pagurus. Its parasites include viruses, such as the white spot syndrome virus, various bacteria that cause dark lesions on the exoskeleton, and Hematodinium-like dinoflagellates that cause "pink crab disease". Other microscopic pathogens include fungi, microsporidians, paramyxeans and ciliates. Cancer pagurus is also targeted by metazoan parasites, including trematodes and parasitic barnacles. A number of sessile animals occasionally settle as epibionts on the exoskeleton of C. pagurus, including barnacles, sea anemones, serpulid polychaetes such as Janua pagenstecheri, bryozoans and saddle oysters.
Cancer pagurus is heavily exploited commercially throughout its range, being the most commercially important crab species in Western Europe. The crabs are caught using crab pots (similar to lobster pots) which are placed offshore and baited. The catch of C. pagurus has increased steadily, rising from 26,000 tonnes in 1978 to 60,000 t in 2007, of which more than 70% was caught around the British Isles. The fishery is widely dispersed around the British and Irish coasts, and C. pagurus is thought to be overfished across much of this area. Most of the edible crabs caught by the British fleet are exported live for sale in France and Spain.
A number of legal restrictions apply to the catching of Cancer pagurus. It is illegal to catch "berried" crabs (females carrying eggs), but since ovigerous females remain in pits dug in the sediment and do not feed, fishing pressure does not affect the supply of larvae. Minimum landing sizes (MLS) for C. pagurus are set by both the European Union technical regulations and by the UK government. Different minimum sizes are employed in different geographical areas, to reflect differences in the crab's growth rate across its range. In particular, the "Cromer crab" fishery along the coasts of Suffolk, Norfolk and Lincolnshire is subject to a MLS of 115 mm (4.5 in), rather than the 140 mm (5.5 in) MLS in most of the species' range. An intermediate value of 130 mm (5.1 in) is used in the rest of the North Sea between the 56th parallel north and the Essex–Kent border, and in the Irish Sea south of 55° N. Around Devon, Cornwall and the Isles of Scilly, there is a separate MLS for males (160 mm or 6.3 in) and females (140 mm or 5.5 in). The Norwegian catch is 8,500 tons annually, compared to 20,000 tons in the United Kingdom, 13,000 tons in Ireland, 8,500 tons in France, and a total 45,000 tons globally.
Around one third of the weight of an adult edible crab is meat, of which one third is white meat from the claws, and two thirds is brown meat from the body. It is used to make "dressed crab", in which the meat is arranged in the cleaned shell with other foodstuffs, soups such as bisque or bouillabaisse, pâtés, mousses and hot soufflés.
Taxonomy and systematics
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According to the rules of the International Code of Zoological Nomenclature, Cancer pagurus was first described by Carl Linnaeus in 1758, in the tenth edition of his Systema Naturae, which marks the starting point of zoological nomenclature. It was chosen to be the type species of the genus Cancer by Pierre André Latreille in 1810. The specific epithet pagurus is a Latin word, deriving from the Ancient Greek πάγουρος (pagouros), which, alongside "κάρκινος" (karkinos), was used to refer to edible marine crabs; neither classical term can be confidently assigned to a particular species.
Although the genus Cancer formerly included most crabs, it has since been restricted to eight species. Within that set of closely related species, the closest relative of C. pagurus is the Jonah crab, Cancer borealis, from the east coast of North America.