Approximately one-quarter of the anthropogenic carbon dioxide released into the atmosphere each year is absorbed by the global oceans, causing measurable declines in surface ocean pH, carbonate ion concentration ([CO32−]), and saturation state of carbonate minerals (Ω)1. This process, referred to as ocean acidification, represents a major threat to marine ecosystems, in particular marine calcifiers such as oysters, crabs, and corals. Laboratory and field studies2,3 have shown that calcification rates of many organisms decrease with declining pH, [CO32−], and Ω. Coral reefs are widely regarded as one of the most vulnerable marine ecosystems to ocean acidification, in part because the very architecture of the ecosystem is reliant on carbonate-secreting organisms4. Acidification-induced reductions in calcification are projected to shift coral reefs from a state of net accretion to one of net dissolution this century5. While retrospective studies show large-scale declines in coral, and community, calcification over recent decades6,7,8,9,10,11,12, determining the contribution of ocean acidification to these changes is difficult, if not impossible, owing to the confounding effects of other environmental factors such as temperature. Here we quantify the net calcification response of a coral reef flat to alkalinity enrichment, and show that, when ocean chemistry is restored closer to pre-industrial conditions, net community calcification increases. In providing results from the first seawater chemistry manipulation experiment of a natural coral reef community, we provide evidence that net community calcification is depressed compared with values expected for pre-industrial conditions, indicating that ocean acidification may already be impairing coral reef growth.

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We thank R. Dunbar for the use of his laboratory and D. Mucciarone for laboratory training and assistance; the Australian Institute of Marine Science for scientific and technical support; Y. Estrada for graphics assistance; and the following people for their support in the field and/or laboratory: M. Byrne, A. Chai, R. Graham, T. Hill, D. Kline, B. Kravitz, J. Reiffel, D. Ross, E. Shaw, and the staff of the One Tree Island Research Station. Expedition and staff support was provided by the Carnegie Institution for Science. Some additional support for staff, but not expedition expenses, was provided by the Fund for Innovative Climate and Energy Research. This work was permitted by the Great Barrier Reef Marine Park Authority under permit G14/36863.1.

Author information


  1. Department of Global Ecology, Carnegie Institution for Science, Stanford, California 94305, USA

    • Rebecca Albright
    • , Lilian Caldeira
    • , Lester Kwiatkowski
    • , Jana K. Maclaren
    • , Yana Nebuchina
    • , Julia Pongratz
    • , Katharine L. Ricke
    • , Kenneth Schneider
    • , Marine Sesboüé
    • , Kai Zhu
    •  & Ken Caldeira
  2. Bodega Marine Laboratory, University of California, Davis, Bodega Bay, California 94923, USA

    • Jessica Hosfelt
    •  & Aaron Ninokawa
  3. Stanford Nano Shared Facilities, Stanford University, Stanford, California 94305, USA

    • Jana K. Maclaren
  4. Department of Genetics, Stanford University School of Medicine, Stanford, California 94305, USA

    • Benjamin M. Mason
  5. Max Planck Institute for Meteorology, Bundesstraße 53, 20146 Hamburg, Germany

    • Julia Pongratz
  6. Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, New York 14853, USA

    • Katharine L. Ricke
  7. The Interuniversity Institute for Marine Sciences, The H. Steinitz Marine Biology Laboratory, The Hebrew University of Jerusalem, Eilat, Israel

    • Tanya Rivlin
  8. The Fredy and Nadine Herrman Institute of Earth Sciences, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Jerusalem, Israel

    • Tanya Rivlin
  9. Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel

    • Kenneth Schneider
  10. Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA

    • Kathryn Shamberger
  11. Texas A&M University, College Station, Texas 77843, USA

    • Kathryn Shamberger
  12. Institute for Oceanographic and Limnological Research, Haifa, Israel

    • Jacob Silverman
  13. School of Medical Sciences, The University of Sydney, Sydney, New South Wales 2006, Australia

    • Kennedy Wolfe
  14. Department of Biology, Stanford University, Stanford, California 94305, USA

    • Kai Zhu
  15. Department of BioSciences, Rice University, Houston, Texas 77005, USA

    • Kai Zhu


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R.A., J.K.M., K.Sc., J.S., and K.C. conceived and designed the project. J.K.M., K.Sc., J.S., J.P., K.L.R., and K.Sh. conducted pilot studies and collected preliminary data. R.A., L.K., L.C., B.M.M., Y.N., T.R., M.S., K.W., A.N., J.H., and K.C. performed the experiments. R.A. and K.C. performed the computational analyses. K.Z. assisted with statistical analyses. R.A. wrote the manuscript with input from K.C. All co-authors reviewed and approved the final manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Rebecca Albright.

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Supplementary information

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  1. 1.

    Supplementary Information

    This file contains Supplementary Methods, Supplementary Notes, Supplementary Equations | Mathematical explanation (and computer code) of multivariate regression approach used to calculate alkalinity-dye ratios (slopes) and mean background alkalinities (y-intercepts), Supplementary Equations for calculating calcification, the mathematical explanation of mixed effects model and Supplementary Notes regarding underlying hypotheses.

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  1. 1.

    Supplementary Table 1

    This table contains the raw data for chemical and physical parameters across all days and station locations (measured and calculated). Details regarding measurements and associated errors are provided in the Methods.

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