Foraging behaviour of the epaulette shark Hemiscyllium ocellatum is not affected by elevated CO₂

Abstract

Abstract Increased oceanic uptake of atmospheric carbon dioxide (CO₂) is a threat to marine organisms and ecosystems. Among the most dramatic consequences predicted to date are behavioural impairments in marine fish which appear to be caused by the interference of elevated CO₂ with a key neurotransmitter receptor in the brain. In this study, we tested the effects of elevated CO₂ on the foraging and shelter-seeking behaviours of the reef-dwelling epaulette shark, Hemiscyllium ocellatum. Juvenile sharks were exposed for 30 d to control CO₂ (400 µatm) and two elevated CO₂ treatments (615 and 910 µatm), consistent with medium- and high-end projections for ocean PCO₂ by 2100. Contrary to the effects observed in teleosts and in some other sharks, behaviour of the epaulette shark was unaffected by elevated CO₂. A potential explanation is the remarkable adaptation of H. ocellatum to low environmental oxygen conditions (hypoxia) and diel fluctuations in CO₂ encountered in their shallow reef habitat. This ability translates into behavioural tolerance of near-future ocean acidification, suggesting that behavioural tolerance and subsequent adaptation to projected future CO₂ levels might be possible in some other fish, if adaptation can keep pace with the rate of rising CO₂ levels.