Distribution: Mya arenaria is found most abundantly in intertidal and shallow subtidal areas but can reach 192 m depth in the subtidal (Strasser, 1999). The majority of clams >50 mm are found in sediment between 15 - 20 cm deep in the Wadden Sea, but may burrow up to 40 cm deep. As they grow adults live deeper in the sediment, their siphons growing accordingly and large clams establish a permanent burrow. Young clams (up to 50 mm) can burrow again if disturbed. However the foot becomes much reduced and shorter in larger specimens. With increasing size it becomes more difficult for exposed specimens to raise the shell into position and therefore. if disturbed, fewer large than small individuals manage to reburrow. For example, 62% of small clams (35-50mm), 39% of medium sized (51-65 mm) and only 21% of large clams (66-75 mm) had reburrowed within 48 hours (Pfitzenmeyer & Drobeck, 1967).

Global distribution: Mya arenaria became extinct on the east coasts of the Pacific and Atlantic during the glaciations of the Pleistocene. It subsequently colonized the European coast between the 13 th and 17 th centuries, possibly introduced by the Vikings (as food or bait) (Eno et al., 1997; Eno et al., 2000; Strasser, 1999). Mya arenaria has been reported from Kamchatka to southern Japan and China, however these records may have been confused with Mya japonica (Strasser, 1999). Strasser (1999) also regarded additional records from Iceland, the Mediterranean and Florida as dubious. Mya arenaria probably invaded the Pacific east coast as a by-product of oyster transplants but was later intentionally introduced as a commercial fishery. It was probably introduced into the Black Sea around 1960 as larvae in the ballast waters of Baltic Sea tankers (Strasser, 1999) . Strasser (1999) notes that although introduction may have been effected by man its present distribution is also the result of significant natural expansion.