Background
The authors write that "according to the IPCC (2007) models, atmospheric CO2 is predicted to rise to 540-970 ppm by the end of this century and reach a maximum of approximately 1,900 ppm when the world's fossil fuel reserves are fully exploited," while noting that "a substantial number of laboratory studies have suggested a decline in coral calcification with a rise in seawater pCO2." However, they say that recent studies "have postulated that the sensitivity of corals to elevated levels of CO2 is potentially more diverse than previously considered," citing the works of Fabricius et al. (2011), Pandolfi et al. (2011) and Rodolfo-Metalpa et al. (2011).

What was done
Intrigued by these new and diverse findings, Takahashi and Kurihara measured the rates of calcification, respiration and photosynthesis of the tropical coral Acropora digitifera - along with the coral's zooxanthellae density - under near-natural summertime temperature and sunlight conditions for a period of five weeks.

What was learned
The two Japanese researchers found that these "key physiological parameters" were not affected by either predicted mid-range CO2 concentrations (pCO2 = 744 ppm, pH = 7.97, Ωarag = 2.6) or by high CO2 concentrations (pCO2 = 2,142 ppm, pH = 7.56, Ωarag = 1.1) over the 35-day period of their experiment. In addition, they state that there was "no significant correlation between calcification rate and seawater aragonite saturation (Ωarag)" and "no evidence of CO2 impact on bleaching."

What it means
Contrary to what many climate alarmists have long contended, there is mounting evidence that suggests that the negative consequences they predict for the world's marine life in a future high-CO2 world are by no means assured, nor are they likely to be widespread.

References
Fabricius, K.E., Langdon, C., Uthicke, S., Humphrey, C., Noonan, S., De'ath, G., Okazaki, R., Muehllehner, N., Glas, M.S. and Lough, J.M. 2011. Losers and winners in coral reefs acclimatized to elevated carbon dioxide concentrations. Nature Climate Change 1: 165-169.

IPCC. 2007. The Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom.

Pandolfi, J.M., Connolly, S.R., Marshall, D.J. and Cohen, A.L. 2011. Projecting coral reef futures under global warming and ocean acidification. Science 333: 418-422.

Rodolfo-Metalpa, R., Houlbreque, F., Tambutte, E., Boisson, F., Baggini, C., Patti, F.P., Jeffree, R., Fine, M., Foggo, A., Gattuso, J.P. and Hall-Spencer, J.M. 2011. Coral and mollusk resistance to ocean acidification adversely affected by warming. Nature Climate Change 1: 308-312.