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Negligible Effects of Ocean Acidification on a Juvenile Coral Reef Fish

Paper Reviewed
Sundin, J., Amcoff, M., Mateos-González, F., Raby, G.D. and Clark, T.D. 2019. Long-term acclimation to near-future ocean acidification has negligible effects on energetic attributes in a juvenile coral reef fish. Oecologia 190: 689-702.

Writing as background for their study, Sundin et al. (2019) note that so-called ocean acidification is projected to increase the energy use of marine fish by means of various physiological and behavioral mechanisms. This hypothesis, they say, is "based on a theoretical framework suggesting that detrimental effects on energy use are caused by plasma acid-base disruption in response to hypercapnic acidosis, potentially in combination with a malfunction of the gamma aminobutyric acid type A (GABAA) receptors in the brain." However, they correctly note that "the existing empirical evidence testing these effects primarily stems from studies that exposed fish to elevated CO2 for a few days and measured [only] a small number of traits." Consequently, there exists ample reasoning to question the validity of this hypothesis. And thus, they set out to conduct their own study of the subject.

Their work focused on juvenile spiny chromis damselfish (Acanthochromis poluacanthus), where following three months of acclimation to projected CO2 levels at the end of this century (i.e., 1000 µatm) they examined a range of energetic traits, comparing responses to juveniles reared under ambient seawater pH.

So what did their study reveal?

As described by the authors, they report that (1) "somatic growth and otolith size and shape were unaffected by the CO2 treatment across 3 months of development in comparison with control fish (~420 µatm)," (2) "swimming activity during behavioral assays was initially higher in the elevated CO2 group, but this effect dissipated within ~25 minutes following handling," and (3) "the transient higher activity of fish under elevated CO2 was not associated with a detectable difference in the rate of oxygen uptake nor was it mediated by GABAA neurotransmitter interference because treatment with a GABAA antagonist (gabazine) did not abolish the CO2 treatment effect."

In light of the above, Sundin et al. say that their findings "demonstrate that end-of-century levels of CO2 may have negligible effects on a variety of energetic traits in at least some fishes, and they add to a growing dichotomy across studies in this field of research." Indeed they do, as more and more studies continue to show so-called ocean to be a non-problem.

Posted 12 September 2019