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Coral and mollusc resistance to ocean acidification adversely affected by warming


Increasing atmospheric carbon dioxide (CO2) concentrations are expectedto decrease surface ocean pH by 0.3–0.5 units by 2100 (refs 1, 2), lowering the carbonate ion concentration of surfacewaters. This rapid acidification is predicted to dramatically decrease calcification in many marine organisms3,4. Reduced skeletal growth under increased CO2 levels has already been shown for corals, molluscs and many other marine organisms4,5,6,7,8,9. The impact of acidification on the ability of individual species to calcify has remained elusive, however, as measuring net calcification fails to disentangle the relative contributions of gross calcification and dissolution rates on growth. Here, we show that corals and molluscs transplanted along gradients of carbonate saturation state at Mediterranean CO2 vents are able to calcify and grow at even faster than normal rates when exposed to the high CO2 levels projected for the next 300 years. Calcifiers remain at risk, however, owing to the dissolution of exposed shells and skeletons that occurs as pH levels fall. Our results show that tissues and external organic layers play a major role in protecting shells and skeletons from corrosive sea water, limiting dissolution and allowing organisms to calcify10,11. Our combined field and laboratory results demonstrate that the adverse effects of global warming are exacerbated when high temperatures coincide with acidification.

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Figure 1: Species transplanted along a pH gradient near volcanic CO2 vents off Ischia, Italy.
Figure 2: Gross calcification of M. galloprovincialis measured in aquaria over a three-week period at pHT 7.4 and 8.1.
Figure 3: Calcification of P. caerulea measured in aquaria at pHT 6.8 and 8.0.
Figure 4: Underwater and scanning electron microscopy images of B. europaea transplanted along a CO2 gradient off Ischia.
Figure 5: Calcification rates of corals transplanted along a CO2 gradient off Ischia.


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We thank all collaborators from Stazione Zoologica ‘A. Dohrn’ for their help during fieldwork, D. Allemand and C. Ferrier-Pagès for helpful discussions, and J-F. Comanducci, F. Oberhänsli and J-L. Teyssié for their help during radiotracer experiments. Comments by P. Mumby and J. Ries improved this manuscript. This work was funded by the Prince Albert II of Monaco Foundation, the International Atomic Energy Agency (IAEA-NAML, Monaco, which is grateful to the Government of the Principality of Monaco for the support provided to its Environment Laboratories), Save our Seas Foundation, an EU MARES studentship and the EU ‘Mediterranean Sea Acidification under a changing climate’ project (MedSeA; grant agreement 265103). The work contributes to the European Project on Ocean Acidification (EPOCA; grant agreement 211384).

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R.R-M. and F.B. designed the study. Most experiments were performed by R.R-M., who wrote the paper in collaboration with F.H., J.M.H-S., M.F. and J-P.G. Coral radiotracer incorporation was performed by F.H. Scanning electron microscopy was performed by E.T. on corals and C.B. on mussels. A.F. performed the statistical analysis. All authors read and commented on the manuscript.

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Correspondence to R. Rodolfo-Metalpa.

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Rodolfo-Metalpa, R., Houlbrèque, F., Tambutté, É. et al. Coral and mollusc resistance to ocean acidification adversely affected by warming. Nature Clim Change 1, 308–312 (2011).

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