Growth rates: Mya arenaria generally grows fastest in its first years with growth rate decreasing with age, although linear rates of growth have also been reported (Strasser, 1999). Growth is rapid in favourable conditions but rates vary with location, e.g. Mya sp. grew to 51 mm in 6-7 years in Alaska, but this size was attained in 1.5 years in Connecticut (Brousseau & Baglivo, 1987). Similarly, marketable size ( 4-5 cm long) was reached within 1.5 years in Chesapeake Bay, but took 5 years in New Brunswick, Canada. Growth rates are affected by population density, sediment type, salinity, emergence time, water flow rates, disturbance, latitude and pollution (Newell & Hidu, 1986; Strasser, 1999).

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.

• in New Hampshire densities of spat ranged from 21 -8,200 /m² from 1975-1980 depending on the year (Newel & Hidu, 1986);
• adults (up to 25 mm and occasionally 40 mm) and large numbers of juveniles were subject to bedload sediment transport (up to 790 individuals /m /day in sheltered sites and 2,600 individuals /m /day in exposed) in Nova Scotia;
• in the above population bedload transport in exposed conditions accounted for 10 fold increase in clam density in September followed by a significant decrease by November and complete removal of newly settled spat (Emerson & Grant, 1991);
• Brousseau (1978b) estimated that 0.1% of egg production survived to successful settlement;
• Newell & Hidu (1986) suggested that <1% of settled spat must mature and reproduce in order to sustain the population;
• high larval and juvenile mortality decreases with age and size levelling off towards age of first reproduction, with estimates of 88% mortality at 2-4.9 mm falling to <10% at >30 mm, and is highest in summer when predators are most abundant (Brousseau, 1978b; Strasser, 1999);
• high densities of settling spat on a shallow exposed shore in southern Sweden in summer were swept away by storms in autumn and early winter (Olafsson et al.,1994);
• predation was blamed for a reduction in newly settled spat from 6000/m² to zero in the subtidal in Virginia (Lucy, 1976 cited by Newell & Hidu, 1986);
• Strasser et al., (1999) noted that sites of high adult densities do not deter settling spat or prevent successful recruitment, but the presence of Arenicola marina may prevent development to adulthood due to bioturbation.