• in New Jersey, (U.S.A) specimens as old as 53 years (13.6 cm) were recorded (Ropes & Murawski, 1983);
• in Georges Bank, (U.S.A) specimens as old as 93 years (13 cm) were recorded (Ropes & Murawski, 1983);
• whereas, a specimen 10.7 cm in length was estimated to be 221 years old in Massachusetts (U.S.A) (Ropes & Murawski, 1983).

• in Whitsand Bay, (UK) individuals grew on average 0 -1.5 mm/yr.;
• whereas off the coast of Long Island, (U.S.A) individuals grew 0.56 mm/yr. in 1970 and 11.7 mm/yr. in 1980; and
• specimens from New Jersey grew an average of 1 mm in 1.6 years (Kennish et al., 1994; cited in Cargnelli et al., 1999a).

Abundance
In the southeast North Sea, the average density of adults >10 mm in length was 7 specimens per 100 m². The highest abundances of spat and adults were recorded in the central regions of the North Sea with 21 individuals >10 mm per 100 m² (Witbaard & Bergman, 2003). The northern North Sea (Fladden Grounds) was dominated by juveniles with 28,600 individuals per 100 m² (Witbaard & Bergman, 2003). In Kiel Bay, Baltic Sea, recorded abundances were 50 /m² but, no size was recorded (Rees & Dare, 1993).

Biomass / Production
In major areas of the northwest Atlantic the standing stock was (expressed as wet meat weight) over 119,000 km², an average of 10 g/m², with a maximum (over 19,000 km²) of 16 g/m² (Murawski & Serchuk, 1989; cited in Rees & Dare, 1993). The total live shell weight /flesh weight ratio was not stated but was presumed to be 2:1 or 3:1). In Kiel Bay, the annual production was estimated to be 15 g ash free dry weight (AFDW) / m² and the biomass was estimated to be 44.4 g AFDW /m² (Rees & Dare, 1993).

Respiration
Arctica islandica like many other bivalves is able to respire aerobically and anaerobically. The change from aerobic to anaerobic respiration in bivalves usually occurs when oxygen levels in the water are reduced. However, Arctica islandica may experience periods of self induced anaerobiosis (Taylor, 1976).

Arctica islandica has only short siphons and siphonal contact with the water cannot be maintained when they burrow several centimetres beneath the sea bed. When this occurs they are able to respire anaerobically. No obvious rhythmic pattern has been detected but these periods of inactivity can last up to 10 days (Taylor, 1976). The heart rate of Arctica islandica after long periods of shell closure usually takes over 20 hours to return to normal (in Mytilus edulis this is accomplished in a few minutes). This behaviour in Arctica islandica is apparently self induced (Oeschger, 1990) since no stimulus that initiates either burrowing or a return to the surface has been identified. It was suggested that this behaviour is a likely response to hypoxic conditions however, previous studies showed that Arctica islandica was readily able to deal with hypoxic conditions. Other suggestions for this self induced burrowing behaviour included saving energy and a reduction in the risk of predation, as Arctica islandica would be less accessible to potential predators such as large starfish. However, more knowledge of their ecology is required (Taylor, 1976).