Acidification and hypoxia interactively affect metabolism in embryos, but not larvae, of the coastal forage fish .

Ocean acidification is occurring in conjunction with warming and deoxygenation as a result of anthropogenic greenhouse gas emissions. Multistressor experiments are critically needed to better understand the sensitivity of marine organisms to these concurrent changes. Growth and survival responses to acidification have been documented for many marine species, but studies that explore underlying physiological mechanisms of carbon dioxide (CO) sensitivity are less common. We investigated oxygen consumption rates as proxies for metabolic responses in embryos and newly hatched larvae of an estuarine forage fish (Atlantic silverside, ) to factorial combinations of CO×temperature or CO×oxygen. Metabolic rates of embryos and larvae significantly increased with temperature, but partial pressure of CO ( ) alone did not affect metabolic rates in any experiment. However, there was a significant interaction between  and partial pressure of oxygen ( ) in embryos, because metabolic rates were unaffected by  level at ambient , but decreased with declining  under elevated For larvae, however,  and  had no significant effect on metabolic rates. Our findings suggest high individual variability in metabolic responses to high , perhaps owing to parental effects and time of spawning. We conclude that early life metabolism is largely resilient to elevated  in this species, but that acidification likely influences energetic responses and thus vulnerability to hypoxia.