Effects of Ocean Acidification on the Life History and Behaviour of Tropical Marine Fishes

Experimental studies with tropical species have been at the forefront of testing the effects of ocean acidification on marine fishes. With some exceptions, basic life-history traits such as growth and development appear to relatively unaffected by projected future CO₂ levels, at least in the reef fishes tested to date. Reproductive output may even been enhanced in high CO₂. However, near-future CO₂ levels interfere with sensory functions and behaviours in tropical marine fishes. Changes include increased activity and boldness, impaired decision making, inability to learn, and altered auditory, visual and olfactory preferences. These sensory and behavioural changes affect a range of ecological processes, including predator-prey and competitive interactions, navigation and habitat selection. The underlying mechanism responsible for sensory and behavioural effects appears to be interference of elevated CO₂ with brain neurotransmitter function, a previously unrecognized threat of ocean acidification. Furthermore, there appears to be limited capacity for within and between generation acclimation of behaviour to high CO₂, which contrasts with findings for life history traits. Behavioural effects of rising CO₂ levels may be a more immediate threat to tropical marine fishes than physiological effects on individual life-histories.