Sensitivity to ocean acidification differs between populations of the Sydney rock oyster: Role of filtration and ion-regulatory capacities.

Understanding mechanisms of intraspecific variation in resilience to environmental drivers is key to predict species' adaptive potential. Recent studies show a higher CO resilience of Sydney rock oysters selectively bred for increased growth and disease resistance ('selected oysters') compared to the wild population. We tested whether the higher resilience of selected oysters correlates with an increased ability to compensate for CO-induced acid-base disturbances. After 7 weeks of exposure to elevated seawater PCO (1100 μatm), wild oysters had a lower extracellular pH (pH = 7.54 ± 0.02 (control) vs. 7.40 ± 0.03 (elevated PCO)) and increased hemolymph PCO whereas extracellular acid-base status of selected oysters remained unaffected. However, differing pH values between oyster types were not linked to altered metabolic costs of major ion regulators (Na/K-ATPase, H-ATPase and Na/H-exchanger) in gill and mantle tissues. Our findings suggest that selected oysters possess an increased systemic capacity to eliminate metabolic CO, possibly through higher and energetically more efficient filtration rates and associated gas exchange. Thus, effective filtration and CO resilience might be positively correlated traits in oysters.