From particle attachment to space-filling coral skeletons

Chang Yu Sun, Cayla A. Stifler, Rajesh V. Chopdekar, Connor A. Schmidt, Ganesh Parida, Vanessa Schoeppler, Benjamin I. Fordyce, Jack H. Brau, Tali Mass, Sylvie Tambutté, Pupa U.P.A. Gilbert

Research output: Contribution to journalArticlepeer-review

Abstract

Reef-building corals and their aragonite (CaCO3) skeletons support entire reef ecosystems, yet their formation mechanism is poorly understood. Here we used synchrotron spectromicroscopy to observe the nanoscale mineralogy of fresh, forming skeletons from six species spanning all reef-forming coral morphologies: Branching, encrusting, massive, and table. In all species, hydrated and anhydrous amorphous calcium carbonate nanoparticles were precursors for skeletal growth, as previously observed in a single species. The amorphous precursors here were observed in tissue, between tissue and skeleton, and at growth fronts of the skeleton, within a low-density nano- or microporous layer varying in thickness from 7 to 20 μm. Brunauer-Emmett-Teller measurements, however, indicated that the mature skeletons at the microscale were space-filling, comparable to single crystals of geologic aragonite. Nanoparticles alone can never fill space completely, thus ion-by-ion filling must be invoked to fill interstitial pores. Such ion-by-ion diffusion and attachment may occur from the supersaturated calcifying fluid known to exist in corals, or from a dense liquid precursor, observed in synthetic systems but never in biogenic ones. Concomitant particle attachment and ion-by-ion filling was previously observed in synthetic calcite rhombohedra, but never in aragonite pseudohexagonal prisms, synthetic or biogenic, as observed here. Models for biomineral growth, isotope incorporation, and coral skeletons’ resilience to ocean warming and acidification must take into account the dual formation mechanism, including particle attachment and ion-by-ion space filling.

Original languageEnglish
Pages (from-to)30159-30170
Number of pages12
JournalProceedings of the National Academy of Sciences of the United States of America
Volume117
Issue number48
DOIs
StatePublished - 1 Dec 2020

Bibliographical note

Publisher Copyright:
© 2020 National Academy of Sciences. All rights reserved.

Keywords

  • Coral skeleton formation | PEEM | spectromicroscopy | biomineral | aragonite

ASJC Scopus subject areas

  • General

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