The decline effect - its not just for psychology and sociology!

From Meta-analysis reveals an extreme “decline effect” in the impacts of ocean acidification on fish behavior by Jeff C. Clements, Josefin Sundin, Timothy D. Clark, and Fredrik Jutfelt.  From the Abstract:

Ocean acidification—decreasing oceanic pH resulting from the uptake of excess atmospheric CO2—has the potential to affect marine life in the future. Among the possible consequences, a series of studies on coral reef fish suggested that the direct effects of acidification on fish behavior may be extreme and have broad ecological ramifications. Recent studies documenting a lack of effect of experimental ocean acidification on fish behavior, however, call this prediction into question. Indeed, the phenomenon of decreasing effect sizes over time is not uncommon and is typically referred to as the “decline effect.” Here, we explore the consistency and robustness of scientific evidence over the past decade regarding direct effects of ocean acidification on fish behavior. Using a systematic review and meta-analysis of 91 studies empirically testing effects of ocean acidification on fish behavior, we provide quantitative evidence that the research to date on this topic is characterized by a decline effect, where large effects in initial studies have all but disappeared in subsequent studies over a decade. The decline effect in this field cannot be explained by 3 likely biological explanations, including increasing proportions of studies examining (1) cold-water species; (2) nonolfactory-associated behaviors; and (3) nonlarval life stages. Furthermore, the vast majority of studies with large effect sizes in this field tend to be characterized by low sample sizes, yet are published in high-impact journals and have a disproportionate influence on the field in terms of citations. We contend that ocean acidification has a negligible direct impact on fish behavior, and we advocate for improved approaches to minimize the potential for a decline effect in future avenues of research.

I have two separate questions and this answers the second.  What is the empirical evidence for ocean acidification and 2) what is the measured impact of that acidification.  In terms of ocean acidification, I have read a lot of claims but do not have a good sense for the reality.  I accept that it can be both real and consequential on a local level but I don't have good sense about overall acidification.

This paper has a preliminary answer at least a part of the second question.

We contend that ocean acidification has a negligible direct impact on fish behavior, and we advocate for improved approaches to minimize the potential for a decline effect in future avenues of research. 

The decline effect - its not just for psychology and sociology!

It does prompt the unbidden question.  Are there any fields in which an initial postulated effect actually turns out be bigger and more reliably documented when the size and discipline of the studies improve?

Can't think of one but it would be interesting to see one.