Paper Reviewed
Cominassi, L., Moyano, M., Claireaux, G., Howald, S., Mark, F.C., Zambonino-Infante, J.-L., Le Bayon, N. and Peck, M.A. 2020. Combined effects of ocean acidification and temperature on larval and juvenile growth, development and swimming performance of European sea bass (Dicentrarchus labrax). PLoS ONE 14: e0221283, doi.org/10.1371/journal.pone.0221283.

In presenting the rationale for their study, Cominassi et al. (2020) write "gaining a mechanistic, physiologically-based understanding of how ocean acidification and warming affect marine flora and fauna is essential for reliable projections of future effects of climate change." And so it was that they set out to obtain such an understanding for a key commercial and recreational fish species home to the northeast Atlantic Ocean and Mediterranean Sea, the European sea bass (Dicentrarchus labrax). More specifically, they "examined the effects of ocean acidification and warming on the somatic growth, development and swimming capacity throughout the larval and early juvenile phase of sea bass reared at two temperatures (15°C and 20°C) and three PCO2 levels (650, 1150, 1700 µatm; pH 8.0, 7.8, 7.6)." It was the authors' expectation that "increased levels of PCO2 might negatively affect the growth and/or swimming ability of larvae due to poorly developed acid-base regulation and the need to partition energy between homeostasis-related mechanisms and ecologically important activities."

So, was their hypothesis proven correct?

As presented in their own words, Cominassi et al. write "contrary to our expectations, the results of the present study indicated that life-long exposure to ocean acidification had no significant effect on the somatic growth rate and swimming capacity of sea bass larvae." Such findings, they add "are in accordance with those reported in a recent meta-analysis conducted by Cattano et al. (2018), highlighting no overall effects of high CO2 on growth," or "in a number of other studies testing routine swimming characteristics or critical swimming speed in marine fish larvae exposed to ocean acidification." However the authors did report larval growth (body height and body weight) were enhanced in the higher temperature treatment, which morphological differences were "related to a faster development at the warmer temperature."

Based on the above findings, in the Conclusion section of their paper, Cominassi et al. write "European sea bass larvae are not impacted by projected future increases in levels of PCO2 thanks to the use of physiological mechanisms allowing them to maintain growth and swimming performance." And they also say "our study adds to the growing number of studies reporting no effects of ocean acidification or ocean acidification and warming on the swimming performance of marine fish larvae." Consequently, the non-findings of the present study are actually quite revealing, indicating the ocean acidification scare is likely just that for marine fish -- a scare!

Reference
Cattano, C., Claudet, J., Domenici, P. and Milazzo, M. 2018. Living in a high CO2 world: a global meta-analysis shows multiple trait-mediated fish responses to ocean acidification. Ecological Monographs 88: 320-335.