Ocean Acidification

Replying to P. L. Munday et al. Nature https://doi.org/10.1038/s41586-020-2803-x (2020)

Pioneering papers by Munday and colleagues^1,2 have reported profound effects of end-of-century ocean acidification—simulated by experimentally elevated CO₂ levels in seawater—on the behaviour of coral reef fishes, such as extreme attraction of prey species to the chemical cues of their predators. Later studies by the same group reported that a range of other behaviours of coral reef fishes, including swimming activity, behavioural lateralization, homing and different predator avoidance behaviours, were also impaired by ocean acidification³ and that predator-escape behaviours in a coral reef mollusc were also impaired through the same physiological mechanism reported for fishes (that is, through effects on ‘GABA_A-like receptors’), which led to the idea that “elevated-CO₂ could cause behavioural impairment in a broad suite of marine animals”⁴. In 2014, we initiated experiments to further explore the physiological mechanism(s) that impaired coral reef fish behaviour in elevated levels of CO₂; however, we immediately ran into a problem: despite several attempts, and many improvements to the standard methodology used in this field, we were unable to observe an effect of ocean acidification on fish behaviour. Our initial goal changed from what was meant to be a series of original experiments into a three-year effort to transparently examine behavioural effects of ocean acidification in coral reef fishes⁵; the findings of our study are the basis for the accompanying Comment by Munday et al.⁶.