Rebuttal of Clark et al. research paper

A group of thirteen researchers from six countries has released a new scientific paper rejecting an earlier study claiming ocean acidification has no effects of the behaviour of coral reef fishes.

Earlier this year, a paper by Clark et al. published in Nature claimed that previous experiments on the effects of elevated CO2 on reef fish behaviour could not be repeated, and argued ocean acidification has no effects on the behaviours of coral reef fishes.

In a comprehensive rebuttal published in Nature, lead author Professor Philip Munday from the Centre of Excellence for Coral Reef Studies at James Cook University said there are fundamental methodological differences between the studies conducted in the “provocative” Clark et al. article and the earlier studies with which they made direct comparison.

“There are so many fundamental differences in what Clark et al. have done compared with the previous studies that the comparisons are invalid,” Prof Munday said.

The authors of the rebuttal argue that experiments conducted by Clark et al. differed in at least 16 critical ways compared with previous research.

“Clark et al. claim to have closely repeated earlier studies, but failed to replicate key species, used different life stages and ecological histories, and altered methods in critical ways that reduce the likelihood of detecting ocean acidification effects.”

Prof Munday said that contrary to their assertions, Clark et al. did not closely replicate the methods of past studies, some conducted over a decade ago. Instead, they made fundamental changes to flume design and methodology that would have affected results. In addition, their experimental treatments lacked the stability needed to meet necessary standards and were much more variable than in previous studies.

“The evidence that elevated CO2 can affect fish behaviour is overwhelming,” says Prof Göran Nilsson, a co-author from the University of Oslo. “Over 85 peer-reviewed papers by many different authors have demonstrated that elevated CO2 can affect the behaviour of fish from coral reefs and other habitats, including at least 8 papers by the authors of Clark et al., which they fail to acknowledge in their paper. They also fail to address the striking result that fish exposed to elevated CO2 have altered behaviour and reduced survival in the field.”

“A reproducibility crisis in science is inevitable if no attempt is made to accurately replicate previous work and to acknowledge other vital evidence,” Prof Munday said.

Prof Munday said scientists are still increasing their understanding of the impact of ocean acidification on fish behaviour.

“Since the earliest experiments in this field were published, we have learnt that not all species are equally affected, and with factors such as sensory compensation, CO2 fluctuations, high temperature and risk history diminishing, or even reversing, the behavioural effects of elevated CO2 on reef fish.”

“By contrast, recent studies report dramatic effects of elevated CO2 on the survival of early life stages of some temperate fishes. We still have much to learn before generalisations about the impacts of elevated CO2 on wild fish populations are possible,” Prof Munday said.

The paper has been published in the journal Nature and is available at: https://rdcu.be/b8PTq

Clark et al have published responses to the rebuttal paper, and Munday at el have provided additional detailed responses available at: https://doi.org/10.25903/7rz7-4640

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