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7899848 
Journal Article 
Amorphous calcium carbonate particles form coral skeletons 
Mass, T; Giuffre, AJ; Sun, CY; Stifler, CA; Frazier, MJ; Neder, M; Tamura, N; Stan, CV; Marcus, MA; Gilbert, PUPA 
2017 
1 
Proceedings of the National Academy of Sciences of the United States of America
ISSN: 0027-8424
EISSN: 1091-6490 
National Academy of Sciences 
114 
37 
E7670-E7678 
English 
28847944 
WOS:000410293400003 
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. © 2017, National Academy of Sciences. All rights reserved. 
Calcification crisis; Mesocrystal; Ocean acidification; PEEM; Vital effects; calcium carbonate; calcium carbonate; mineral; sea water; acidification; Article; bleaching; controlled study; coral; coral reef; crystallization; dissolution; ecosystem; hydration; nonhuman; priority journal; sea; skeleton; Stylophora pistillata; surface property; warming; animal; Anthozoa; bone mineralization; chemistry; growth, development and aging; metabolism; pH; physiology; Animals; Anthozoa; Calcification, Physiologic; Calcium Carbonate; Coral Reefs; Crystallization; Ecosystem; Hydrogen-Ion Concentration; Minerals; Seawater