Ideas and Perspectives: When ocean acidification experiments are not the same, repeatability is not tested

Can experimental studies on the behavioural impacts of ocean acidification be trusted? That question was raised in early 2020 when a high-profile paper failed to corroborate previously observed responses of coral reef fish to high CO2. New information on the methodologies used in the “replicated” studies now provides a plausible explanation: the experimental conditions were substantially different. High sensitivity to test conditions is characteristic of ocean acidification research; such response variability shows that effects are complex, interacting with many other factors. Open-minded assessment of all research results, both negative and positive, remains the best way to develop process-based understanding. As in other fields, replication studies in ocean acidification are most likely to contribute to scientific advancement when carried out in a spirit of collaboration rather than confrontation.