Description: 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.

Description: Respiration rate of meiofauna is difficult to measure, and the response to variations in the environmental oxygen concentrations has so far been mainly addressed through behavioral investigation. We investigated the effect of different oxygen concentrations on the physiology of the marine platyhelminth Macrostomum lignano. Respiration was measured using batches of 20 animals in a glass microtiter plate equipped with optical oxygen sensor spots. At higher oxygen saturations (〉60%), animals showed a clear oxyconforming behavior. However, below this values, the flatworms kept respiration rates constant at 0.064 ± 0.001 nmol O2•l-1•h-1•ind-1 down to 3 kPa po2, evidencing a highly developed metabolic regulating capacity. Physiological changes related to tissue oxygenation were assessed using live imaging techniques with different fluorophores in animals maintained in normoxic (21 kPa), hyperoxic (40 kPa), near anoxic (≈0 kPa) conditions and subjected to anoxia/re-oxygenation. Ageladine-A and BCECF both indicated that pHi under near anoxia increases by about 0.07 to 0.10 units. Mitochondrial membrane potential, Δψm, was less polarized higher in anoxic and hyperoxic compared to normoxic conditions (JC1). Staining with ROS sensitive dyes, DHE for detection of superoxide anion (O2•-) formation and C-H2DFFDA for other ROS species aside from O2•- (H2O2, HOO• and ONOO-)for H2O2 formation, both showed increased ROS formation following anoxia reoxygenation treatment. Animals exposed to hyperoxic, normoxic and anoxic treatments displayed no significant differences in superoxide O2•- formation, whereas mitochondrial H2O2 ROS formation (as detected by C-H2DFFDA) was higher after hyperoxic exposure and lowest under near anoxia compared to the normoxic control group. M. lignano seems to be a species tolerant to a wide range of oxygen concentrations (being able to maintain aerobic metabolism from extremely low po2 and up to hyperoxic conditions) which is an essential prerequisite for successfully dealing with the drastic environmental oxygen variations that occur within intertidal sediments.