Common Shore Crab (Carcinus maenas)
Also known as the Green Crab and European Crab, the common shore crab is an extremely common species of crab which is found throughout all of Britain and Ireland’s coastlines. The common shore crab will be found wherever there is some rock or weed cover in water down to 100m deep. This species of crab grows to a maximum size of around 8-9cm across the carapace. Despite being known as the green crab the colour is actually highly variable and can be anything from brownish to green or red/orange. The front edge of the carapace has a serrated edge and eight legs and two claws are present. The claws are capable of delivering a mildly painful nip. The common shore crab will feed on anything it can find. They will scour the seabed for any form of dead marine animals and will happily consume dead or rotting fish. The will also consume shellfish, marine worms or pretty much any other form of animal matter they come across, including other common shore crabs. Crabs become prey themselves with predatory fish such as cod and bass taking crabs, and large marine birds will also feed on crabs they find. The common shore crab must undergo a process of shedding its shell and growing a new one once or twice a year. During this vulnerable time the common shore crab is easy prey for predators and therefore hides itself away until the process is complete. It is during this time the crab is known as a ‘peeler’ and is of most use to the angler as bait. More information is available on the peeling process in the section on peeler crabs as bait.
Status as an Invasive Species
The common shore crab is native to Europe and has a wide distribution stretching from Scandinavia and northern Europe, throughout the Mediterranean and along the northern coast of Africa (in the Mediterranean and African waters there is also the closely related but separate species of Carcinus aestuarii). However, the common shore crab was found off the coasts of North America in the late 1800s, and since then has been steadily progressing its range around this region. This has been a major cause of concern to American and Canadian authorities, as C. maenas has the potential to cause much damage to commercially valuable clam, mussel and scallop beds. The common shore crab can also harm other local (and commercially important) species of crab and lobsters by competing with them for resources. It is thought that C. maenas is faster than many local American species, and its more dexterous and powerful claws give it an advantage when competing for food. This pushes out local species and has the potential to vastly reduce their numbers. Common shore crab have also been confirmed as being present off the coast of Argentina, South Africa and Australia. It is believed that ships travelling from Europe and releasing ballast water may be a major cause of the common shore crab to foreign waters, while the importing of live lobsters may also play a role as common shore crabs can be present in the seaweed and gravel that the lobsters are packed in. The IUCN’s Invasive Species Specialist Group classes the common shore crab as one of the top 100 worst invasive species in the world and blames this species for the collapse of the soft-shell clam industry in both New England and Nova Scotia. They calculate that the common shore crab causes around $22 million of damage in the United States and Canada every year.
Velvet Swimming Crab (Necora puber) Also known as the Albanian Swimming Crab and the Devil Crab.
The velvet swimming crab is a commonly found throughout the UK and Ireland. It is easily distinguishable from the common shore crab by the fact that the back legs are adapted into flat paddle-like flippers to aid swimming, and the eyes are red (hence the alternative name of devil crab). It can also be covered in fine velvety like hairs. The velvet swimming crab grows to a maximum size of around 8-9cm across the carapace. Other than its better (but still limited) swimming ability the velvet swimming crab feeds and sheds its shell in a similar pattern to the common shore crab and can also deliver a minor nip to anyone carelessly handling this species.
Brown Crab (Cancer pagurus) Also known as the Edible Crab.
The brown crab is by far the largest crab species in British waters, with the carapace of a fully grown adult being around 20cm across, and in exceptional specimens 25-30cm. The upper shell of the crab is oval shaped and usually an orange-red colour with paler undersides. Like all of the crab species in British waters they have eight legs and two, very large and powerful claws, with the pincers usually being black. One of the most distinguishable features of this species of crab is the pattern which runs along the edge of the carapace which is usually described as resembling a pie crust. Due to the very large and powerful claws the brown crab can cause a very painful nip to humans it comes across. The brown crab is distributed all around the British Isles and is also present in the Arctic and Baltic seas and has a limited distribution in the Mediterranean.
Like most crabs the brown crab will be found in areas where there are rocks and weed to provide cover. The crab will hide in cracks and under weed and emerge to forage for food. Like all crab species they are voracious consumers of anything they can find. They will happily feed on dead marine organisms and shellfish and will use their strength and power to ambush other crabs, especially the common shore crab. Smaller, younger brown crabs tend to live in the intertidal zone, with crabs moving into deeper water as they get older and grown in size. The largest, fully-grown brown crabs will live in water down to around one hundred metres deep. Brown crabs need to be around 12-15cm across the carapace before they can reproduce. Brown crabs will shell and enter the peeler phase often in their first few years of life when they are growing rapidly, but this slows down to shedding their shell once a year or less as they get older. It is thought that brown crabs have a natural lifespan of 30-40 years, and in exceptional circumstances can live for over one hundred years.
Brown crabs are extremely commercially important and the brown crab fishery in British waters is the largest in the world. The brown crab provides white flesh from the claws and brown flesh from its body. Around one third of the overall weight of the crab is edible as crab meat. Despite the importance of this species there is very little known about overall stock numbers, or the extent to which current fishing intensity is effecting stocks. Crabs are caught by lowering baited crab pots into the sea. This is one of the most selective methods of commercial fishing and allows small, undersized and berried (egg carrying) females to be returned to the sea. However, the brown crab fishery could be threatened by more mechanised methods of fishing with are less selective. Anywhere selling brown crabs with a carapace of 13cm or under should be boycotted as there is no possibility that crabs of this size would have been able to reproduce before capture and they should have been returned to the sea.
Common Hermit Crab (Pagurus bernhardus)
While there are many species of hermit crab around the UK by far the most common is P. bernhardus, the common hermit crab. It is common around the UK, Iceland, the Faroe Islands and Scandinavia, but its range does not extend into the warmer waters of the Mediterrenean. Unlike all other crab species the common peeler crab does not have its own carapace and must find the discarded shell of another sea creature and make this its home. The hermit crab will then move itself around with the shell on its back and retreat into the shell when it is threatened by a predator. As the hermit crab grows it must leave its original shell and search for a larger and more suitable home. Hermit crab sometimes form a symbiotic relationship with a white ragworm. The worm will also live in the shell with the crab and eat any excess food matter that gets into the shell. Hermit crabs will crawl along the seabed and will eat any decomposing plant or animal matter that they come across. They also have the ability to filter feed and consume plankton and other forms of microscopic sea creatures. Generally, the smaller hermit crabs of a centimetre or so in length will be found around the intertidal zone. When hermit crabs are fully grown as three or four centimetres long they will move into deeper water and be found at depths down to two hundred metres. Common hermit crabs have some use as a bait for sea anglers. More information can be found here.
European Spider Crab (Maja squinado)
A species of crab that is found in the English Channel and along the west coast of England, Scotland and Ireland. The European Spider Crab is unlikely to be confused with any other species of crab in British waters. It has a circular body, usually light orange in colour and covered in bumps and has small spines running along the edge. The body can be 20cm across. Its legs are usually a darker orange and are very long and have two joints in them. The claws are relatively small and are on the end of very long arms that also have two joints in them. The European Spider Crab feeds on plant matter, shellfish and will also eat animals such as starfish, brittle stars and marine worms. They also undertake some form of migration where they move in great numbers (presumably as a defence against predators) into deeper water. This migration is poorly understood but may be linked to breeding. There is a limited fishery for this species of crab, mostly concentrated around ports in the south-west of England. Although there is no demand for this species of crab from UK consumers it is widely eaten in Spain, France and other parts of Europe, and almost all British catches of this species are exported.
Bristly Crab (Pilumnus hirtellus)
Also known as the hairy crab, this species of crab is very small, being just 2-3cm across when fully grown. This species of crab is mostly found around the south and west of the British Isles, and generally stays within the intertidal zone. The body and legs of the bristly crab are reddish-brown in colour and are covered in bristly hair-like structures which give this crab its name. Like all crabs it has eight legs and two claws, with one claw (usually the right) being larger than the other. Its diet is primarily made up of dead and rotting marine creatures.
Masked Crab (Corystes cassivelaunus)
The masked crab is a species of crab which is present mostly around the south and west of the British Isles, although smaller isolated populations are present elsewhere across the country and is also found throughout European waters. It is a small species of crab with a carapace measuring a few centimetres across. It lives on sandy and muddy seabeds and buries itself into the sediment with its long antenna poking out. They generally live just outside the intertidal zone and down to depths of around one hundred metres. It feeds on marine worms and any other small creatures which are found in the sand and sediment where this crab is present.