Ocean Acidification

Globally, non-native species (NNS) have been introduced and now often entirely replace native species in captive aquaculture; in part, a result of a perceived greater resilience of NSS to climate change and disease. Here, the effects of ocean acidification and warming on metabolic rate, feeding rate, and somatic growth was assessed using two co-occurring species of oysters – the introduced Pacific oyster Magallana gigas (formerly Crassostrea gigas), and native flat oyster Ostrea edulis. Biological responses to increased temperature and pCO₂ combinations were tested, the effects differing between species. Metabolic rates and energetic demands of both species were increased by warming but not by elevated pCO₂. While acidification and warming did not affect the clearance rate of O. edulis, M. gigas displayed a 40% decrease at ∼750 ppm pCO₂. Similarly, the condition index of O. edulis was unaffected, but that of M. gigas was negatively impacted by warming, likely due to increased energetic demands that were not compensated for by increased feeding. These findings suggest differing stress from anthropogenic CO₂ emissions between species and contrary to expectations, this was higher in introduced M. gigas than in the native O. edulis. If these laboratory findings hold true for populations in the wild, then continued CO₂ emissions can be expected to adversely affect the functioning and structure of M. gigas populations with significant ecological and economic repercussions, especially for aquaculture. Our findings strengthen arguments in favour of investment in O. edulis restoration in UK waters.