Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 13, issue 5
Biogeosciences, 13, 1717-1722, 2016
https://doi.org/10.5194/bg-13-1717-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 13, 1717-1722, 2016
https://doi.org/10.5194/bg-13-1717-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 18 Mar 2016

Research article | 18 Mar 2016

Skeletal mineralogy of coral recruits under high temperature and pCO2

T. Foster1,2,3 and P. L. Clode2,4 T. Foster and P. L. Clode
  • 1UWA School of Earth and Environment, University of Western Australia, Crawley, Western Australia, 6009, Australia
  • 2UWA Oceans Institute, University of Western Australia, Crawley, Western Australia, 6009, Australia
  • 3ARC Centre of Excellence for Coral Reef Studies, University of Western Australia, Crawley, Western Australia 6009, Australia
  • 4Centre for Microscopy, Characterisation and Analysis, University of Western Australia, Crawley, Western Australia, 6009, Australia

Abstract. Aragonite, which is the polymorph of CaCO3 precipitated by modern corals during skeletal formation, has a higher solubility than the more stable polymorph calcite. This higher solubility may leave animals that produce aragonitic skeletons more vulnerable to anthropogenic ocean acidification. It is therefore important to determine whether scleractinian corals have the plasticity to adapt and produce calcite in their skeletons in response to changing environmental conditions. Both high pCO2 and lower MgCa ratios in seawater are thought to have driven changes in the skeletal mineralogy of major marine calcifiers in the past ∼ 540Ma. Experimentally reduced MgCa ratios in ambient seawater have been shown to induce some calcite precipitation in both adult and newly settled modern corals; however, the impact of high pCO2 on the mineralogy of recruits is unknown. Here we determined the skeletal mineralogy of 1-month-old Acropora spicifera coral recruits grown under high temperature (+3°C) and pCO2 (∼ 900µatm) conditions, using X-ray diffraction and Raman spectroscopy. We found that newly settled coral recruits produced entirely aragonitic skeletons regardless of the treatment. Our results show that elevated pCO2 alone is unlikely to drive changes in the skeletal mineralogy of young corals. Not having an ability to switch from aragonite to calcite precipitation may leave corals and ultimately coral reef ecosystems more susceptible to predicted ocean acidification. An important area for prospective research would be the investigation of the combined impact of high pCO2 and reduced MgCa ratio on coral skeletal mineralogy.

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In recent years much research has focussed on whether corals will be able to build their skeletons under predicted ocean acidification. One strategy corals may employ is changing the mineralogy of their skeletons from aragonite to the less soluble polymorph of calcium carbonate; calcite. Here we show that newly settled coral recruits are unable to produce calcite in their skeletons under near-future elevations in pCO2, which may leave them more vulnerable to ocean acidification.
In recent years much research has focussed on whether corals will be able to build their...
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