We compared six biogeographically and climatically distinct population of 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). Different geographic locations, covering a temperature and salinity gradient of 3.7–9.3 °C and 20–35 ppt from the Norwegian coast, White Sea, Iceland, Kattegat, Kiel Bay and German Bight. The bivalve shells were used as age recorders by counting annual growth bands. Maximum lifespan in different populations varied between 30 and 192 y. The exceptionally long lifespan of A. islandica cannot be exclusively explained by a better-established antioxidant defense system. Extreme longevity observed in some North Atlantic populations seems to be grounded in its very low lifetime mass specific respiration, in combination with stable maintenance of antioxidant protection over life in mature specimens. The shorter-lived populations have the highest metabolic rates and show no metabolic response (Q10) when warmed to higher temperature. Low and fluctuating salinity in Baltic exerts a stress, which enhances respiration rates and shortens longevity.