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

Abstract. Can experimental studies on the impacts of ocean acidification be trusted? That question was raised in early 2020 when a high-profile paper failed to corroborate previously-observed impacts of high CO₂ on the behaviour of coral reef fish. New information on the methodologies used in the replicated studies now provides the 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 of those responses. Whilst replication studies can provide valuable insights and challenges, they can unfortunately also be counter-productive to scientific advancement if carried out in a spirit of confrontation rather than collaboration.