Marine animal behaviour in a high CO2 ocean

Recently, the effects of ocean acidification (OA) on marine animal behaviour have garnered considerable attention, as they can impact biological interactions and, in turn, ecosystem structure and functioning. We reviewed current published literature on OA and marine behaviour and synthesize current understanding of how a high CO2 ocean may impact animal behaviour, elucidate critical unknowns, and provide suggestions for future research. Although studies have focused equally on vertebrates and invertebrates, vertebrate studies have primarily focused on coral reef fishes, in contrast to the broader diversity of invertebrate taxa studied. A quantitative synthesis of the direction and magnitude of change in behaviours from current conditions under OA scenarios suggests primarily negative impacts that vary depending on species, ecosystem, and behaviour. The interactive effects of co-occurring environmental parameters with increasing CO2 elicit effects different from those observed under elevated CO2 alone. Although 12% of studies have incorporated multiple factors, only one study has examined the effects of carbonate system variability on the behaviour of a marine animal. Altered GABA(A) receptor functioning under elevated CO2 appears responsible for many behavioural responses; however, this mechanism is unlikely to be universal. We recommend a new focus on determining the effects of elevated CO2 on marine animal behaviour in the context of multiple environmental drivers and future carbonate system variability, and the mechanisms governing the association between acid-base regulation and GABA(A) receptor functioning. This knowledge could explain observed species-specificity in behavioural responses to OA and lend to a unifying theory of OA effects on marine animal behaviour.