Ocean acidification – deceasing oceanic pH resulting from the uptake of excess atmospheric CO2 – is expected to affect marine life in the future. Among the possible consequences, a series of studies on coral reef fishes suggested that the direct effects of acidification on fish behaviour will be the most catastrophic. Recent studies documenting a lack of effect of experimental ocean acidification on fish behaviour, however, call this dire prediction into question. Here, we critically assess the past decade of ocean acidification research regarding direct effects on fish behaviour. Using a meta-analysis, we provide quantitative evidence that the research to date on this topic is strongly characterized by a phenomenon known as the “decline effect”, where large effects have all but disappeared over a decade. The decline effect in this field cannot be explained biologically, but is strongly associated with well-known biases to which the process of science is generally prone. We contend that ocean acidification does not have as much of a direct impact on fish behaviour as previously thought, and we advocate for improved approaches to minimize the potential for a decline effect in future avenues of research.
Clements J., Sundin J., Clark T. D., & Jutfelt F., in press. An extreme decline effect in ocean acidification ecology. EcoEvoRxiv Preprints. Article.