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False Alarm: Study Refutes Findings that Acidification Affects Fish Behavior

The Scientist

New experimental results refute a decade of research suggesting that increased ocean acidification—the process by which increasingly available atmospheric carbon dioxide is absorbed by the ocean, lowering its pH—alters the behavior of coral reef fish, researchers reported today in Nature. 

reef damselfish
Damselfishes swim on the Great Barrier Reef in Australia. New research suggests that ocean acidification won’t impair these fishes’ behavior, in contrast to earlier studies. FREDRIK JUTFELT/NORWEGIAN UNIVERSITY OF SCIENCE AND TECHNOLOGY

The researchers saw no significant difference in the animals’ behavior in several different laboratory-based tests in water with varying pH.

Many studies published over the last 10 years reported that when the pH of seawater in the lab goes down to levels that match future predictions, coral reef fish behave differently. Specifically, rather than avoid areas where chemical signals indicate a predator’s presence, the fish would gravitate toward these areas. Acidification also changes their activity levels and their preference for turning right or left to avoid an obstacle in their path.

“The initial results being published in this field were incredible from a biological perspective. The magnitude of the effect of ocean acidification (elevated CO2) on fish behaviour was huge,” Timothy Clark, a biologist at Deakin University and the lead author of the latest study, tells The Scientist in an email. “Yet there had been no attempt by independent research groups to replicate these profound findings.

Co-author Josephine Sundin looks into an exposure tan on Lizard Island in Australia in 2014.TIM CLARK

So the team set out to replicate the findings and possibly investigate their physiological bases using more than 900 individual fish from six species over three years. The fish, which came from the northern portion of the Great Barrier Reef or an Australian aquarium, were acclimated to different levels of acidification for four days or more and then exposed to a behavioral cue—such as an obstacle to swim around or chemicals that signal that a predator is near.

The scientists didn’t record any substantial differences in the ways the fish responded to their environments based on altered pH and concluded that ocean acidification has negligible effects on the behavior of coral reef fish.

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