Near-future carbon dioxide levels alter fish behaviour by interfering with neurotransmitter function

Predicted future CO2 levels have been found to alter sensory responses and behaviour of marine fishes. Changes include increased boldness and activity, loss of behavioural lateralization, altered auditory preferences and impaired. olfactory function(1-5). Impaired olfactory function makes larval fish attracted to odours they normally avoid, including ones from predators and unfavourable habitats(1,3). These behavioural alterations have significant effects on mortality that may have far-reaching implications for population replenishment, community structure and ecosystem function(2,6). However, the underlying mechanism linking high CO2 to these diverse responses has been unknown. Here we show that abnormal olfactory preferences and loss of behavioural lateralization exhibited by two species of larval coral reef fish exposed to high CO2 can be rapidly and effectively reversed by treatment with an antagonist of the GABA-A receptor. GABA-A is a major neurotransmitter receptor in the vertebrate brain. Thus, our results indicate that high CO2 interferes with neurotransmitter function, a hitherto unrecognized threat to marine populations and ecosystems. Given the ubiquity and conserved function of GABA-A receptors, we predict that rising CO2 levels could cause sensory and behavioural impairment in a wide range of marine species, especially those that tightly control their acid-base balance through regulatory changes in HCO3- and Cl- levels.