Study Finds Research on Climate Change Effects on Ocean ‘Biased’ and ‘Overinflated’

Assorted reef fish swim above a staghorn coral colony as it grows on the Great Barrier Reef off the coast of Cairns, Australia, on Oct. 25, 2019. Lucas Jackson/Reuters

An analysis and review by academics from the Norwegian University of Science and Technology have concluded that research papers published prior to 2014 into the environmental effect of ocean acidification on fish behaviour were overinflated and biased due to the steep decline in impact observed in studies published after 2014.

The team, led by Jeff Clements, stated that many of the studies that found there to be great effects on fish behaviours were biased, resulting in “inflated results.”

Ocean acidification is a product of climate change; around one-quarter of carbon dioxide released through greenhouse emissions are dissolved into the sea and increases the acidity of seawater.

This can be problematic for some marine organisms such as coral and some plankton, which need basic molecules such as carbonate to form their skeleton and shells. When the seawater becomes more acidic, the carbonate of their skeletons become neutralised and therefore dissolves in the water.

Additionally, among the many consequences of ocean acidification, studies prior to 2014 showed that it also had great impacts on behaviours of fish such as clownfish having difficulty navigating their way home.

The authors however noted that even if the effects of such studies were true, recent studies published after 2014 all showed a very drastic decline in the magnitude of effect sizes on fish causing the author’s to theorise that the previous results were affected by bias.

Researchers “selectively publishing impressive results in prestigious journals and also to journals—particularly high-impact journals” can result in “the proliferation of studies reporting strong effects, even though they may not be true and can fuel citation bias,” the study said.

“As results showing strong effects are often published more readily, and in higher-impact journals, than studies showing weak or null results,” the authors wrote.

The authors argued that journals that show high impacts are often published in journals that favour striking effects and therefore have a lot of influence due to being more frequently cited than studies showing weaker relationships, with “early studies with large effect sizes remain the most highly cited among all articles in our dataset.”

Additionally, studies that show high impacts often have a small sample size can be unreliable as the results may not be reflective of the actual outcome in reality due to the fish chosen to be studied may not show all the traits and features that are present in the actual population.

To resolve this problem, the authors suggested that “future ocean acidification studies on fish behaviour should employ a sample size greater than 30 fish per treatment in order to be considered reliable.”

Timothy Clark, a co-author of the paper and a professor from Deakin University previously led a paper in 2020 that concluded that ocean acidification had a “negligible impact” on fish in the coral reefs.

He said that though the negative effects of carbon dioxide emissions on rising sea temperatures are “well established” as devasting for coral reef systems, and ocean acidification is “detrimental to calcifying organisms like oysters and corals” during vulnerable life changes; a change in fish behaviour is not one of the consequences.

“Elevated CO2 does not meaningfully alter activity levels or behavioural lateralisation—that is left-right turning preference—nor does it alter the response of fish to the chemical cues released by predators,” he said.

The Australian Institute for Marine Science (AIMS) has previously led studies that concluded that ocean acidification “robbed” fish’s fear of predators in 2014 and in 2008 published a paper that linked ocean acidification with reef fish losing their way; both of were contradicted in Clark’s study in 2020.

Clements and his colleagues concluded that though their study has demonstrated that the field of ocean acidification on fish behaviour “has seemingly settled in a good place with respect to realistic effect sizes, it has taken 10 years to get there.”

Recent studies continue to cite the earlier reports that show higher impacts on fish behaviour and ecology and the authors suggested that a “shift in mindset” is still needed within this research field.

“Early exaggeration of effects can have real impacts on the process of science and the scientists themselves,” therefore proper steps to eliminate bias should mitigate the impacts and achieve a real understanding and progress within the field.