Do corals form their skeletons by precipitation from solution or by attachment of amorphous precursor particles as observed in other minerals and biominerals? The classical model assumes precipitation in contrast with observed “vital effects,” that is, deviations from elemental and isotopic compositions at thermodynamic equilibrium. Here, we show direct spectromicroscopy evidence in Stylophora pistillata corals that two amorphous precursors exist, one hydrated and one anhydrous amorphous calcium carbonate (ACC); that these are formed in the tissue as 400-nm particles; and that they attach to the surface of coral skeletons, remain amorphous for hours, and finally, crystallize into aragonite (CaCO3). We show in both coral and synthetic aragonite spherulites that crystal growth by attachment of ACC particles is more than 100 times faster than ion-by-ion growth from solution. Fast growth provides a distinct physiological advantage to corals in the rigors of the reef, a crowded and fiercely competitive ecosystem. Corals are affected by warming-induced bleaching and postmortem dissolution, but the finding here that ACC particles are formed inside tissue may make coral skeleton formation less susceptible to ocean acidification than previously assumed. If this is how other corals form their skeletons, perhaps this is how a few corals survived past CO2 increases, such as the Paleocene–Eocene Thermal Maximum that occurred 56 Mya.
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - 12 Sep 2017|
Bibliographical noteFunding Information:
ACKNOWLEDGMENTS. We thank Andrew H. Knoll, Steve Weiner, Lia Addadi, and Paul Falkowski for reading the manuscript and suggesting improvements; Elia Beniash for introducing T.M. to P.U.P.A.G.; Paul Falkowski for supplying the corals used for this study; and Jonathan Stillman for use of his aquarium facility at the University of California, Berkeley. We also thank Andreas Scholl (Advanced Light Source) and Palle Von Huth (Center of Microscopy and Imaging, University of Haifa) for their assistance during experiments. T.M. acknowledges support from Israel Science Foundation Grant 312/15 and
United States–Israel Binational Science Foundation Grant BSF-2014035. P.U.P.A.G. acknowledges 80% support from US Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division Award DE-FG02-07ER15899; 19% from National Science Foundation Grant DMR-1603192; and 1% from United States–Israel Binational Science Foundation Grant BSF-2010065. PEEM and microdiffraction experiments were done at the Advanced Light Source, which is a Department of Energy Office of Science User Facility supported by Grant DE-AC02-05CH11231.
© 2017, National Academy of Sciences. All rights reserved.
- Calcification crisis
- Ocean acidification
- Vital effects
ASJC Scopus subject areas