Common shore crab (Carcinus maenas) care guide

Group

Other invertebrates

Other names

Shore crab, Green shore crab, European green crab, Green crab, Cancer maenas

Family

Carcinidae

Origin

North-east Atlantic and Baltic, from Iceland and Norway to North Africa, including all British coasts; invasive elsewhere

Water

saltwater

Maximum size

9 cm

Care level

beginner

Temperament

aggressive

Reef safe

no

Lifespan

3–5 years

Care

The shore crab is the commonest crab on British shores, found in rock pools, estuaries, mud, sand and seaweed. Its shell is up to about 6 cm long and 9 cm wide in its native range, and varies from green to brown, grey or red; the colour is partly inherited but mostly set by habitat, and crabs that delay moulting turn red. Juveniles are often strongly patterned. UK native: this animal is native to Britain. It needs a coldwater (unheated) marine tank, kept cool in summer, and should not be collected from the wild where that is not allowed; check local byelaws and site rules first. Set-up: a large coldwater marine tank or rock-pool tank with rocks, caves, sand and good filtration, and a firm lid. Adults tolerate an exceptional range, 0–30 °C and salinity from about 4 to 52 parts per thousand, so they survive brackish estuaries as well as full sea water, but they live longest kept cool and stable. Keep one per tank unless it is large; they fight and eat each other after moulting. Invasive elsewhere: it is one of the world's most damaging invasive marine species, established in North America, South America, South Africa and Australia. Never release aquarium animals anywhere. Lifespan figure is general guidance, not from a source. Copper: copper-based medicines and some plant fertilisers are toxic to shrimp, snails and most other invertebrates. Never dose them in a tank holding this animal, and read the label of any treatment, fertiliser or algae remover before use. Sources: Wikipedia (en.wikipedia.org/wiki/Carcinusmaenas). Checked October 2026.

Diet

A predator and scavenger. In the wild it eats mussels, clams and other bivalves, worms, small crustaceans (including smaller crabs), young fish and even seagrass seeds. In a tank feed mussel, cockle, prawn, fish pieces, sinking pellets and some seaweed. It eats less in cold water.

Breeding

Females can carry more than 400,000 eggs. The larvae drift offshore through several planktonic stages before settling as tiny crabs on the shore. Breeding is not practical in home aquariums. Males have a narrow, triangular abdominal flap; females have a broad, rounded one.

Compatibility and tank mates

Aggressive and not reef safe. It will eat snails, bivalves, shrimp, other crabs and any fish it can catch, and damages anemones and soft-bodied animals. Keep alone or with robust native fish such as blennies (shannies) that keep out of reach.

Last updated 8 October 2026. Community-edited care guide on Aquatic-Auctions.