Environmental factors such as temperature and salinity regimes shape lifespan in marine ectotherms, and the question is whether the effect is through modification of metabolic reactive oxygen species- (ROS)-producing processes and thus in line with the 'Rate of Living – Free Radical Theory of Aging'. We compared 6 biogeographically and climatically distinct populations of the extremely long-lived ocean quahog Arctica islandica for age-dependent differences in metabolic rates and antioxidant capacities (superoxide dismutase, catalase activity and total glutathione concentration). The temperature and salinity range covered by the sampling locations was 3.7–9.3 °C and 20–35 psu from the Norwegian coast, White Sea, Iceland, Kattegat, Kiel Bay and German Bight. Bivalve shells were used as age recorders by counting annual growth bands. Maximum determined age in different populations varied between 29 and 192 yr. Extreme longevity observed in some North Atlantic Arctica islandica populations seems to be based on its