Paper Reviewed
Von Euw, S., Zhang, Q., Manichev, V., Murali, N., Gross, J., Feldman, L.C., Gustafsson, T., Flach, C., Mendelsohn, R. and Falkowski, P.G. 2017. Biological control of aragonite formation in stony corals. Science 356: 933-938.

Writing as background for their study, Von Euw et al. (2017) note that "the process by which stony corals deposit their calcium carbonate skeleton in the form of aragonite has been extensively discussed for decades without the emergence of a clear consensus," adding that there are presently two prevailing hypotheses to explain it. The first is that it is a physiochemical process, whereas the second argues it is biologically controlled.

Hoping to provide definitive evidence for which of these two hypotheses is valid for stony corals (Stylophora pistillata), the team of ten scientists investigated the biomineralization process by applying "a materials science approach that combines Raman imaging and spectroscopy, scanning helium ion microscopy (SHIM), and solid-state nuclear magnetic resonance (NMR) spectroscopy." Such approach, in the words of the authors, "reveals the crystallization pathway of aragonite in corals and provides unprecedented insights into the relation between the mineral phase and the skeletal organic matrix across different spatial scales." And what did their work reveal in this regard?

Von Euw et al. write that their results "strongly suggest that the ability of corals to calcify is biologically controlled and thus relatively robust. As such, the biological reaction is far from thermodynamic equilibrium, and, hence, biomineralization in stony corals is not simply related to physicochemical parameters such as the equilibrium saturation state of carbonate ions or the bulk pH of seawater." And this finding, as they continue, "is further supported by the fossil record of scleractinian corals," which indicates that "these organisms survived the Paleocene-Eocene Thermal Maximum, which was associated with a very large increase in atmospheric carbon dioxide." Thus, Von Euw et al. conclude that "the results presented here and elsewhere (Mass et al., 2013) suggest that they may retain greater metabolic capability to form aragonite skeletons than commonly supposed." In other words, projected negative impacts of ocean acidification on the calcification of stony corals are unlikely to occur. And that is great news for this, and potentially other, coral species!

Reference
Mass, T., Drake, J.L., Haramaty, L., Kim, J.D., Zelzion, E., Bhattacharya, D., Falkowski, P.G. 2013. Cloning and characterization of four novel coral acid-rich proteins that precipitate carbonates in vitro. Current Biology 23: 1126-1131.