Elevated CO 2 affects anxiety but not a range of other behaviours in juvenile yellowtail kingfish.

Elevated seawater CO can cause a range of behavioural impairments in marine fishes. However, most studies to date have been conducted on small benthic species and very little is known about how higher oceanic CO levels could affect the behaviour of large pelagic species. Here, we tested the effects of elevated CO, and where possible the interacting effects of high temperature, on a range of ecologically important behaviours (anxiety, routine activity, behavioural lateralization and visual acuity) in juvenile yellowtail kingfish, Seriola lalandi. Kingfish were reared from the egg stage to 25 days post-hatch in a full factorial design of ambient and elevated CO (~500 and ~1000 μatm pCO) and temperature (21 °C and 25 °C). The effects of elevated CO were trait-specific with anxiety the only behaviour significantly affected. Juvenile S. lalandi reared at elevated CO spent more time in the dark zone during a standard black-white test, which is indicative of increased anxiety. Exposure to high temperature had no significant effect on any of the behaviours tested. Overall, our results suggest that juvenile S. lalandi are largely behaviourally tolerant to future ocean acidification and warming. Given the ecological and economic importance of large pelagic fish species more studies investigating the effect of future climate change are urgently needed.