The edible crab is distributed between northern Africa and Northern Norway, sometimes as far north as Finnmark. However, main living area is around the British Isles, including Ireland, while the French and Norwegian coasts are also locations for significant populations.
Being a true marine species, the edible crab is only found in waters with high and relatively stable salinity. They settle and grow on hard bottoms, which is the typical habitat for this species. They feed on all kinds of bottoms. Mature females move into sandy bottom areas, to dig themselves into the sediment when spawning, and where they hide for four to five months before the egg hatch. Except for newly mated females, these crab species is relatively stationary, migrating more vertically, feeding in the upper, warmer shore at night and moving back down into deeper water at daytime. During winter, they often og as deep as 30-50 m, to avoid the cold surface water. Occasionally, crabs have been caught down to 400 m depth. Long migrations are seen only in newly mated females, walking counter-current, to position themselves in hatching areas that enable the larvae to float back with the current to the settling grounds.
Like all crustaceans, the edible crab must shed their shell, ”moult”, to grow. This happens in the warm season, but not necessarily every year in older crabs. It takes a lot of energy and they are very vulnerable during the moult. In large crabs, they can wait for more than one year between each moult.
The crabs mate when the females are moulting and are soft-shelled. It takes 5-7 years to reach mature age, and is usually more than 120 mm wide. The male place his sperm within small packages, ”spermatophores” within the egg channels of the females, where it can be stored for a long time. Having spent so much energy on the shell formation and moult, the females need to feed for 5-6 months until they have developed the eggs to the stage they can be spawned. Spawning and fertilization is usually in late autumn and early winter. The females have by then reached the spawning grounds, where they will stay, more or less dug into the sand and care for the eggs attached to their ”tail”, and feeding very little for the next 5.6 months, until hatching time the next summer.
The nearly microscopic edible crab larvae floats in the upper layers of the water column for up to two months, moulting seven times, before they settle, 2.5 mm wide. The next year they stay in rocky crevices and underneath sea kelp holdfasts and grow through a series of moults to approximately 150 mm.
Edible crabs are omnivorous, eating more or less anything they can find, but are particularly fond of shells and bristle worms. In the very upper regions of the shore, they feed on barnacles. However, being scavengers as well, they are important in renovations of the sea bed.