Ocean acidification impact on coral reef fish behaviour

I’ve seen and heard concerns regarding the potential impact of increased dissolved CO2 in our oceans. Adding CO2 will lower the pH of the oceans. The process is called ‘acidification’, although there is no risk that the oceans would substantially move from their current pH of approximately 8 to being below 7 (i.e. an acid). Irrespective of the nomenclature, the concerns of lower pH remain.

A Scandinavian study has just been published that has monitored the behaviour of coral reef fish over a three year period. This comprehensive study of the effects of ocean acidification challenges previous reports that a more acidic ocean will negatively affect coral reef fish behaviour. The abstract states:

The partial pressure of CO2 in the oceans has increased rapidly over the past century, driving ocean acidification and raising concern for the stability of marine ecosystems1,2,3. Coral reef fishes are predicted to be especially susceptible to end-of-century ocean acidification on the basis of several high-profile papers4,5 that have reported profound behavioural and sensory impairments—for example, complete attraction to the chemical cues of predators under conditions of ocean acidification. Here, we comprehensively and transparently show that—in contrast to previous studies—end-of-century ocean acidification levels have negligible effects on important behaviours of coral reef fishes, such as the avoidance of chemical cues from predators, fish activity levels and behavioural lateralization (left–right turning preference). Using data simulations, we additionally show that the large effect sizes and small within-group variances that have been reported in several previous studies are highly improbable. Together, our findings indicate that the reported effects of ocean acidification on the behaviour of coral reef fishes are not reproducible, suggesting that behavioural perturbations will not be a major consequence for coral reef fishes in high CO2 oceans.

Clark, T.D., Raby, G.D., Roche, D.G. et al. Ocean acidification does not impair the behaviour of coral reef fishes. Nature 577, 370–375 (2020). https://doi.org/10.1038/s41586-019-1903-y
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