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Coral resilience to ocean acidification and global warming through pH up-regulation


Rapidly rising levels of atmospheric CO2 are not only causing ocean warming, but also lowering seawater pH hence the carbonate saturation state of the oceans, on which many marine organisms depend to calcify their skeletons1,2. Using boron isotope systematics3, we show how scleractinian corals up-regulate pH at their site of calcification such that internal changes are approximately one-half of those in ambient seawater. This species-dependent pH-buffering capacity enables aragonitic corals to raise the saturation state of their calcifying medium, thereby increasing calcification rates at little additional energy cost. Using a model of pH regulation combined with abiotic calcification, we show that the enhanced kinetics of calcification owing to higher temperatures has the potential to counter the effects of ocean acidification. Up-regulation of pH, however, is not ubiquitous among calcifying organisms; those lacking this ability are likely to undergo severe declines in calcification as CO2 levels increase. The capacity to up-regulate pH is thus central to the resilience of calcifiers to ocean acidification, although the fate of zooxanthellate corals ultimately depends on the ability of both the photosymbionts and coral host to adapt to rapidly increasing ocean temperatures4.

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Figure 1: Plot of pHT relative to pHcf, determined from boron isotope systematics3 (see Supplementary Information) of aragonitic corals and calcitic foraminifera17.
Figure 2: Percentage change in calcification rates (relative to seawater Ω=4.6) plotted against seawater aragonite saturation state (Ωar).
Figure 3: Future and historical projections of changes in internal saturation state and % changes in coral calcification rates.


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The authors are grateful for financial support from the Australian Research Council Discovery grant DP0986505 awarded to M.M. and J.T. and to the Australian Research Council Centre of Excellence for Coral Reef Studies for support to J.F. and M.M. P.M. is grateful for financial support from the Marie Curie International Outgoing Fellowship (MEDAT-ARCHIVES) and M.M. is supported by a Western Australian Premiers’ Fellowship. This is ISMAR-CNR scientific contribution no. 1745.

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M.M. and J.T. designed the study and J.F., M.M. and P.M. carried out the model simulations. M.M. led the writing with contributions from all authors to the analysis of the results and writing the manuscript.

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Correspondence to Malcolm McCulloch.

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McCulloch, M., Falter, J., Trotter, J. et al. Coral resilience to ocean acidification and global warming through pH up-regulation. Nature Clim Change 2, 623–627 (2012).

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