Losers and winners in coral reefs acclimatized to elevated carbon dioxide concentrations

Journal name:
Nature Climate Change
Year published:
Published online

Experiments have shown that ocean acidification due to rising atmospheric carbon dioxide concentrations has deleterious effects on the performance of many marine organisms1, 2, 3, 4. However, few empirical or modelling studies have addressed the long-term consequences of ocean acidification for marine ecosystems5, 6, 7. Here we show that as pH declines from 8.1 to 7.8 (the change expected if atmospheric carbon dioxide concentrations increase from 390 to 750ppm, consistent with some scenarios for the end of this century) some organisms benefit, but many more lose out. We investigated coral reefs, seagrasses and sediments that are acclimatized to low pH at three cool and shallow volcanic carbon dioxide seeps in Papua New Guinea. At reduced pH, we observed reductions in coral diversity, recruitment and abundances of structurally complex framework builders, and shifts in competitive interactions between taxa. However, coral cover remained constant between pH 8.1 and ~7.8, because massive Porites corals established dominance over structural corals, despite low rates of calcification. Reef development ceased below pH 7.7. Our empirical data from this unique field setting confirm model predictions that ocean acidification, together with temperature stress, will probably lead to severely reduced diversity, structural complexity and resilience of Indo-Pacific coral reefs within this century.

At a glance


  1. Volcanic CO2 seeps of Milne Bay.
    Figure 1: Volcanic CO2 seeps of Milne Bay.

    Seascapes at a, control site (‘low pCO2’: pH~8.1), b, moderate seeps (‘high pCO2’: pH 7.8–8.0), and c, the most intense vents (pH<7.7), showing progressive loss of diversity and structural complexity with increasing pCO2. d, Map of the main seep site along the western shore of Upa-Upasina (marked as grey; map: Supplementary Fig. S1). Colour contours indicate seawater pH, and the letters indicate the approximate locations of seascapes as shown in ac.

  2. Response ratios (high pCO2/low pCO2, averaged across the three reefs), summarizing the observed biotic changes.
    Figure 2: Response ratios (high pCO2/low pCO2, averaged across the three reefs), summarizing the observed biotic changes.

    Differences are significant at the 5% level if the error bars (upper and lower 2SE) do not include the value 1.0. The panels include a, reef communities including hard and soft corals (HC, SC); b, juvenile corals; c, skeletal extension, density and calcification, tissue thickness, colony pigmentation and densities of externally visible macrobioeroders in massive Porites, and linear extension in Pocillopora damicornis; d, seagrass (SG) shoot density, below-ground biomass, diversity, epibiont cover, densities of foraminifera; e, sediment properties and associated calcifying biota. Foram. is Foraminera, sed. is sedimentary and inorg. is inorganic.

  3. Progressive changes in reef biota along a pH gradient at Upa-Upasina Reef.
    Figure 3: Progressive changes in reef biota along a pH gradient at Upa-Upasina Reef.

    Red and blue symbols indicate high and low pCO2 transect sections respectively, and mean pH was predicted from seawater measurements (N=74; Supplementary Fig. S3A and B). The black lines indicate the log-linear fits and the grey bands indicate upper and lower 2SE. Also presented are the percentage variance explained by pH, and the significance of the relationships. Abbreviations as in Fig. 2.

  4. Mean rates of calcification of massive Porites at the Milne Bay seep sites and other Indo-Pacific regions as a function of mean annual sea surface temperature.
    Figure 4: Mean rates of calcification of massive Porites at the Milne Bay seep sites and other Indo-Pacific regions as a function of mean annual sea surface temperature.

    Circles represent colonies from many Indo-Pacific regions (averaged over 1961–1990; N=10–15 colonies per point; from ref. 15). Solid line: linear regression fit, black and grey dashed lines: upper and lower 95% confidence and prediction intervals, respectively. Red triangle and blue square: calcification of massive Porites at high- and low-pCO2 sites, respectively (N=17 and 12 colonies; vertical bars: upper and lower SE).


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Author information


  1. Australian Institute of Marine Science, PMB 3, Townsville, Queensland 4810, Australia

    • Katharina E. Fabricius,
    • Sven Uthicke,
    • Craig Humphrey,
    • Sam Noonan,
    • Glenn De’ath &
    • Janice M. Lough
  2. University of Miami Rosenstiel School of Marine and Atmospheric Science, 4600 Rickenbacker Causeway, Florida 33149, USA

    • Chris Langdon,
    • Remy Okazaki &
    • Nancy Muehllehner
  3. Max-Planck Institute for Marine Microbiology, Department of Biogeochemistry, Celsiusstr. 1, 28395 Bremen, Germany

    • Martin S. Glas


All authors were involved with either fieldwork or data analyses. K.E.F. initiated and designed the study and wrote the manuscript, with contributions from all others. C.L. and R.O. analysed the seawater chemistry, C.H., S.N., K.E.F. and J.M.L. collected and analysed the Porites data, C.L. the in situ coral growth data, K.E.F. and S.N. the reef community data, S.U. the sediments and foraminifera, N.M. and S.U. the seagrass and epibiont data, and G.D. and K.E.F. conducted the statistical analyses.

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