Species-specific effects of near-future CO2 on the respiratory performance of two tropical prey fish and their predator

Ocean surface CO2 levels are increasing in line with rising atmospheric CO2 and could exceed 900 mu atm by year 2100, with extremes above 2000 mu atm in some coastal habitats. The imminent increase in ocean pCO(2) is predicted to have negative consequences for marine fishes, including reduced aerobic performance, but variability among species could be expected. Understanding interspecific responses to ocean acidification is important for predicting the consequences of ocean acidification on communities and ecosystems. In the present study, the effects of exposure to near-future seawater CO2 (860 mu atm) on resting ((M) over dotO(2rest)) and maximum ((M) over dotO(2max)) oxygen consumption rates were determined for three tropical coral reef fish species interlinked through predator-prey relationships: juvenile Pomacentrus moluccensis and Pomacentrus amboinensis, and one of their predators: adult Pseudochromis fuscus. Contrary to predictions, one of the prey species, P. amboinensis, displayed a 28-39% increase in (M) over dotO(2max) after both an acute and four-day exposure to near-future CO2 seawater, while maintaining (M) over dotO(2rest). By contrast, the same treatment had no significant effects on (M) over dotO(2rest) or (M) over dotO(2max) of the other two species. However, acute exposure of P. amboinensis to 1400 and 2400 mu atm CO2 resulted in (M) over dotO(2max) returning to control values. Overall, the findings suggest that: (1) the metabolic costs of living in a near-future CO2 seawater environment were insignificant for the species examined at rest; (2) the (M) over dotO(2max) response of tropical reef species to near-future CO2 seawater can be dependent on the severity of external hypercapnia; and (3) near-future ocean pCO(2) may not be detrimental to aerobic scope of all fish species and it may even augment aerobic scope of some species. The present results also highlight that close phylogenetic relatedness and living in the same environment, does not necessarily imply similar physiological responses to near-future CO2. (c) 2013 Elsevier Inc. All rights reserved.