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Dolomite-rich coralline algae in reefs resist dissolution in acidified conditions

Nature Climate Change volume 3, pages 268272 (2013) | Download Citation


Coral reef ecosystems develop best in high-flow environments but their fragile frameworks are also vulnerable to high wave energy. Wave-resistant algal rims, predominantly made up of the crustose coralline algae (CCA) Porolithon onkodes and P. pachydermum1,2, are therefore critical structural elements for the survival of many shallow coral reefs. Concerns are growing about the susceptibility of CCA to ocean acidification because CCA Mg-calcite skeletons are more susceptible to dissolution under low pH conditions than coral aragonite skeletons3. However, the recent discovery4 of dolomite (Mg0.5Ca0.5(CO3)), a stable carbonate5, in P. onkodes cells necessitates a reappraisal of the impacts of ocean acidification on these CCA. Here we show, using a dissolution experiment, that dried dolomite-rich CCA have 6–10 times lower rates of dissolution than predominantly Mg-calcite CCA in both high-CO2 ( 700 ppm) and control ( 380 ppm) environments, respectively. We reveal this stabilizing mechanism to be a combination of reduced porosity due to dolomite infilling and selective dissolution of other carbonate minerals. Physical break-up proceeds by dissolution of Mg-calcite walls until the dolomitized cell eventually drops out intact. Dolomite-rich CCA frameworks are common in shallow coral reefs globally and our results suggest that it is likely that they will continue to provide protection and stability for coral reef frameworks as CO2 rises.

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Thanks to F. Brink and the team at the ANU Centre for Advanced Microscopy for assistance with SEM work, A. Harvey for CCA samples from Victoria, L. Teneva for differential interference contrast analyses, J. Caves for field work assistance, the FOCE team and staff at Heron Island Research Centre, J. W. Lai and D. Nash for sample preparation. S. Connell for assistance with Heron experiments and J. Roberts for assistance with SEM.

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  1. Research School of Physics, The Australian National University, Acton, Australian Capital Territory 0200, Australia

    • M. C. Nash
  2. Research School of Earth Sciences, The Australian National University, Acton, Australian Capital Territory 0200, Australia

    • B. N. Opdyke
    • , U. Troitzsch
    • , C. Brent
    • , M. Gardner
    •  & J. Prichard
  3. Southern Seas Ecology Laboratories, School of Earth and Environmental Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia

    • B. D. Russell
  4. National Museum of Natural History, Smithsonian Institution, Washington DC 20013, USA

    • W. H. Adey
  5. Takehara Fisheries Research Station, Center for Education and Research of Field Science, Hiroshima University, Minato-machi, Takehara, Hiroshima 725-0024, Japan

    • A. Kato
  6. Griffith School of Environment and Australian Rivers Institute—Coast and Estuaries, Griffith University, Brisbane, Nathan, Queensland 4111, Australia

    • G. Diaz-Pulido
  7. Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093, USA

    • D. I. Kline
  8. Coral Reef Ecosystems Laboratory, School of Biological Sciences, University of Queensland, Brisbane, Queensland 4072, Australia

    • D. I. Kline


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M.C.N. and B.N.O. designed initial project; M.C.N., B.D.R. and D.I.K. carried out Heron Island experimental work and water chemistry measurements; U.T. assisted with subsequent analyses and project design. G.D-P., sample identification and design of experimental tank facilities; A.K. and W.H.A., sample collection and identification. M.C.N., U.T. and W.H.A., SEM. M.C.N. and U.T., XRD analysis. C.B., M.G. and J.P., sample collection, survey, XRD and data analyses. M.C.N. and U.T. wrote and edited the manuscript and all authors contributed.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to M. C. Nash.

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