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Are Effects of Ocean Acidification on Corals Greatly Exaggerated?

Paper Reviewed
Venti, A., Andersson, A. and Langdon, C. 2014. Multiple driving factors explain spatial and temporal variability in coral calcification rates on the Bermuda platform. Coral Reefs 33: 979-997.

Introducing their take on the subject, Venti et al. (2014) relate that negative effects of ocean acidification (OA) on coral calcification rates have been well documented, with a strong correlation being observed between seawater aragonite saturation state (Ωarag) and rates of calcification; but they note that these results "are heavily drawn from controlled aquarium and mesocosm studies, which isolate OA by manipulating seawater inorganic carbon chemistry while keeping other parameters such as light, temperature, salinity, nutrients, and flow rates constant," and this in spite of the fact that much previous research "has shown that coral calcification rates are also a direct function of these parameters," citing the studies of Chalker and Taylor (1975), Koop et al. (2001) and Mass et al. (2010).

In a move designed to atone for these common but significant environmental parameter omissions, the three U.S. scientists studied colonies of Porites astreoides and Diploria strigosa at three different sites spread across the northern Bermuda coral reef platform, where they evaluated the correlations between seasonal average coral growth rates - based on coral density and extension - with mean temperature, light intensity and seawater Ωarag in an effort to determine the relative importance of each parameter. And in doing so, they discovered that the observed seasonal differences in temperature, light and Ωarag could account for approximately 44, 52 and 5%, respectively, of the observed seasonal change in coral calcification rate.

Venti et al.'s take-home message, therefore, is that out in the real world of nature, "the covariance of light and Ωarag can lead to the false conclusion that calcification is more sensitive to Ωarag than it really is," as they write in the concluding sentence of their paper's abstract.

Chalker, B.E. and Taylor, D.L. 1975. Light-enhanced calcification, and the role of oxidative phosphorylation in calcification of the coral Acropora cervicornis. Proceedings of the Royal Society of London B: Biological Science 190: 323-331.

Koop, K., Booth, D., Broadbent, A., Brodie, J., Hoegh-Gulberg, O., Capone, D. and Coll. J. 2001. ENCORE: The effect of nutrient enrichment on coral reefs, synthesis of results and conclusions. Marine Pollution Bulletin 42: 91-120.

Mass, T., Genin, A., Shavit, U., Grinstein, M. and Tchernov, D. 2010. Flow enhances photosynthesis in marine benthic autotrophs by increasing the efflux of oxygen from the organism to the water. Proceedings of the National Academy of Sciences USA 107: 2527-2531.

Posted 14 March 2015