Contrasting responses to salinity and future ocean acidification in arctic populations of the amphipod Gammarus...

Climate change is leading to alterations in salinity and carbonate chemistry in arctic/sub-arctic marine ecosystems. We examined three nominal populations of the circumpolar arctic/subarctic amphipod, Gammarus setosus, along a salinity gradient in the Kongsfjorden-Krossfjorden area of Svalbard. Field and laboratory experiments assessed physiological (haemolymph osmolality and gill Na⁺/K⁺-ATPase activity, NKA) and energetic responses (metabolic rates, MO₂, and Cellular Energy Allocation, CEA). In the field, all populations had similar osmregulatory capacities and MO₂, but lower-salinity populations had lower CEA. Reduced salinity (S = 23) and elevated pCO₂ (~1000 μatm) in the laboratory for one month increased gill NKA activities and reduced CEA in all populations, but increased MO₂ in the higher-salinity population. Elevated pCO₂ did not interact with salinity and had no effect on NKA activities or CEA, but reduced MO₂ in all populations. Reduced CEA in lower-rather than higher-salinity populations may have longer term effects on other energy demanding processes (growth and reproduction).