Cerastoderma edule

In stable sand, mud and muddy gravel below effect of strong wave action, to 200m, and from mid-tide level to ELWS and below in sheltered bays and outer estuaries, where up to 10 000 /sq. metre (small specimens). Does not prosper in brackish water below 20 p.p.t. Short siphons, so confined to near surface of substrate. Very large specimens lie exposed on surface. Water carrying oxygen, plankton, benthic diatoms and organic material enters inhalent siphon to be processed by ctenidium for respiration and food before exiting exhalent siphon.

Size distribution in populations varies with complex of factors including length of immersion /feeding period, competition, and numbers and capabilities of predators at different shore levels. Usually, average size increases and population density decreases from mid-tide level to ELWS. In Britain, average size increases from South to North, reflected in Fishery limits on riddle gauges; 16mm Thames, 19mm S.Wales, 20mm N.Wales, 30mm Outer Hebrides (limits subject to change). Largest specimens in Europe may be in Orkney; over thirty live specimens, 60mm –75mm length, found exposed on sand surface at ELWS on 300m stretch of beach. At this size immune to oyster catchers (major predator, preferred length 20-30mm), and numerous Buccinum undatum present. Beach rarely visited, so human predation minimal.  Causal factor(s) of N-S cline uknown. Archaeological deposits suggest decline in size at places and periods of high human utilization of cockles.

Breeds in Britain late February – early July. Separate sexes release milt or ova into sea. After two or three weeks as a trochophore and veliger larva in the plankton, settles on substrate and metamorphoses into adult form.