A recent study in @nature couldn& #39;t replicate drastic CO2 effects on coral reef #fish behaviour & empirically found no effect of #oceanacidification https://go.nature.com/3hK49UR ">https://go.nature.com/3hK49UR&q...

Our #metaanalysis of the past decade on this topic concurs https://ecoevorxiv.org/k9dby/ ">https://ecoevorxiv.org/k9dby/&qu...

Breakdown threadhttps://abs.twimg.com/emoji/v2/... draggable="false" alt="👇" title="RĂŒckhand Zeigefinger nach unten" aria-label="Emoji: RĂŒckhand Zeigefinger nach unten">
We demonstrate one of the most striking examples of the #DeclineEffect in #ecology to date, w/ reported effects of OA on fish behaviour all but disappearing over past decade

If you’ve never heard of the #DeclineEffect see: https://bit.ly/2EbZX2o ">https://bit.ly/2EbZX2o&q...
Qualitatively the number of studies reporting “strong” effects of #oceanacidification on fish behaviour have plummeted over time
Quantitatively effect size magnitudes (log response ratio) have declined from averages of 3-4 in early pioneering studies to 0.2–0.4 over past 5 years

While highly significant in early years, mean effect size magnitudes have been non-significant from zero for 4 of past 5 years
To check if this #DeclineEffect was due to increasing studies on cold-water species, we removed cold-water studies (b/c these species may be more tolerant to OA than tropical coral reef species)

Nope

But maybe OA only has an effect when some type of cue or stimulus is involved – after all, the biggest effects are with predator cues!

Again, nope

OK, so if it’s not biological, then what could it be? Could it be
 #BIAS!? https://abs.twimg.com/emoji/v2/... draggable="false" alt="đŸ˜±" title="Vor Angst schreiendes Gesicht" aria-label="Emoji: Vor Angst schreiendes Gesicht">
We first checked for methodological bias

Underpowered studies are prone to Type I error & can often detect strong effects when they don’t actually exist

Do studies showing super-strong effects have low sample sizes?

Yep...
We also found that over time, avg n & proportion of studies w/ n>30 have increased

This suggests that the number of fish used in experiments partly explains the #DeclineEffect, but some high-n studies show strong effects, so n is not everything

OK, but lots of fields have underpowered studies – what’s the harm?

Are studies w/ super-strong effects more likely to be published in influential high IF journals & thus get more attention?


.https://abs.twimg.com/emoji/v2/... draggable="false" alt="😬" title="Grimasse schneidendes Gesicht" aria-label="Emoji: Grimasse schneidendes Gesicht">https://abs.twimg.com/emoji/v2/... draggable="false" alt="😬" title="Grimasse schneidendes Gesicht" aria-label="Emoji: Grimasse schneidendes Gesicht">
Like sample size, we also saw that the average IF of journals publishing papers decreased over time

Note the strong blip in IF for 2014 which was accompanied by a similar blip in mean effect size for that year!

Strong evidence for selective publishing
This study provides strong evidence that dramatic reports of OA affecting fish behaviour are probably exaggerated &, frankly, false

The strong effects appear linked w/ methodological bias, selective publication of outstanding effects, and other unexplained phenomena
We suggest that OA-fish behaviour studies be given more weight when n>30 fish per treatment

It is imperative that authors REPORT SAMPLE SIZE PRECISELY!!!!

A massively frustrating part of this study was trying to decipher n – 34% of studies didn’t report it adequately!!
Reviewers & editors can also help here by being skeptical & critical of manuscripts reporting outstanding effects, especially those w/ n<30
We also strongly suggest that unbiased results be published early and alongside studies showing strong effects

How can we do this?

PRE-REGISTRATION! https://go.nature.com/3c2Q43v ">https://go.nature.com/3c2Q43v&q...
First analysis of ‘pre-registered’ studies shows sharp rise in null findings

Logging hypotheses and protocols before performing research seems to work as intended: to reduce publication bias for positive results.

https://go.nature.com/3c2Q43v
It’s also important for null results to be published in high IF journals so they are given equal public weighting

A scary anecdote w/ this paper: it’s been desk rejected by 5 high IF journals that previously published those extreme OA effects, each taking >1 month to decide

Researchers should also incorporate best practices for behavioural studies whenever possible

for example, use published methodological guidelines such as https://bit.ly/2RAUghe ">https://bit.ly/2RAUghe&q... & use automated technologies for recording behaviour if possible
Two‐current choice flumes for testing avoidance and preference in aquatic animals

Aquatic chemical ecology is an important and growing field of research that involves understanding how organisms perceive and respond to chemical cues in their environment. Research assessing the...

https://bit.ly/2RAUghe
Finally, be critical! Especially of early findings w/ large effects

Scientists are good at predicting which studies are likely to replicate & which ones won’t (see https://go.nature.com/3mtsCRK )">https://go.nature.com/3mtsCRK&q... – apply that skepticism early!!
Evaluating the replicability of social science experiments in Nature and Science between 2010 and...

Camerer et al. carried out replications of 21 Science and Nature social science experiments, successfully replicating 13 out of 21 (62%). Effect sizes of replications were about half of the size of...

https://go.nature.com/3mtsCRK
Does #oceanacidification affect marine animals?

In many instances, yeah...

But in light of our results & those of the non-replication @nature study ( https://go.nature.com/3hK49UR ">https://go.nature.com/3hK49UR&q... ), direct effects of OA on fish behaviour are likely small
Ocean acidification does not impair the behaviour of coral reef fishes

In contrast to previous studies, analyses now show that ocean acidification does not perturb important behavioursñ€”such as the avoidance of chemical cues from predatorsñ€”of coral reef fishes.

https://go.nature.com/3hK49UR
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