How does rising atmospheric CO2 affect marine organisms?

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Effects of Elevated CO2 and Temperature on a Temperate Coral
Rodolfo-Metalpa, R., Martin, S., Ferrier-Pages, C. and Gattuso, J.-P. 2010. Response of the temperate coral Cladocora caespitosa to mid- and long-term exposure to pCO2 and temperature levels projected for the year 2100 AD. Biogeosciences 7: 289-300.

The authors write that "anthropogenic CO2 emitted to the atmosphere is absorbed by the oceans leading to decreases in pH, CO32- concentration, and the related CaCO3 saturation state (O) of seawater," and that "as a result, coral calcification is expected to decline dramatically in the future, raising widespread concerns about the future of our oceans in a high-CO2 world (e.g. Hoegh-Guldberg et al., 2007)."

What was done
Rodolfo-Metalpa et al. collected three live colonies of Cladocora caespitosa in the Bay of Villefranche (Ligurian Sea, France) at about 25 meters depth in July 2006 plus three other colonies in February 2007. They divided the colonies into fragments and carefully removed single polyps that they attached to PVC plates and randomly assigned to aquariums that were continuously supplied with unfiltered seawater and maintained at ambient or elevated water temperature (T or T + 3C) in equilibrium with air of ambient or elevated CO2 concentration (400 or 700 ppm), subjecting them to "(1) mid-term perturbations (1 month) in summer and winter conditions of irradiance and temperature, and (2) a long-term perturbation (1 year), mimicking the seasonal changes in temperature and irradiance."

What was learned
The four researchers say that for the Mediterranean zooxanthellate coral, "an increase in CO2, in the range predicted for 2100, does not reduce its calcification rate," and that "an increase in CO2, alone or in combination with elevated temperature, had no significant effect on photosynthesis, photosynthetic efficiency and calcification." However, they report that a 3C rise in temperature in winter resulted in a 72% increase in gross photosynthesis, as well as a significant increase in daytime calcification rate.

What it means
In light of their several significant findings, Rodolfo-Metalpa et al. conclude that "the conventional belief that calcification rates will be affected by ocean acidification may not be widespread in temperate corals." In this regard, for example, they note that Ries et al. (2009) have reported that the calcification rate of the temperate coral Oculina arbuscula is also unaffected by an increase in atmospheric CO2 concentration of up to 840 ppm, and that a large decrease in calcification was only found at a CO2 concentration in excess of 2200 ppm. In addition, they write that "some marine invertebrates may be able to calcify in the face of ocean acidification or, contrary to what is generally expected, may increase their calcification rates as reported on the ophiourid brittlestar Amphiura filiformis (Wood et al., 2008), the seastar Pisaster ochraceus (Gooding et al., 2009) exposed to lower pH (7.8-7.3), the Caribbean coral Madracis mirabilis at pH 7.6 (Jury et al., 2010), and shown for coralline red algae, calcareous green algae, temperate urchins, limpets, crabs, lobsters and shrimp (Ries et al., 2009)." Likewise, they write that there are many cases where "rates of photosynthesis are either not affected (e.g. Langdon et al., 2003; Reynaud et al., 2003; Schneider and Erez, 2006; Marubini et al., 2008) or slightly increased (e.g. Langdon and Atkinson, 2005) at the level of CO2 expected in 2100."

Yes, all is not the "doom and gloom" the world's climate alarmists make it out to be.

Gooding, R.A., Harley, C.D.G. and Tang, E. 2009. Elevated water temperature and carbon dioxide concentration increase the growth of a keystone echinoderm. Proceedings of the National Academy of Sciences USA 106: 9316-9321.

Hoegh-Guldberg, O., Mumby, O.J., Hooten, A.J., Steneck, R.S., Greenfield, P., Gomez, E., Harvell, C.D., Sale, P.F., Edwards, A.J., Caldeira, K., KNowlton, N., Eakin, C.M., Iglesias-Prieto, R., Muthiga, N., Bradbury, R.H., Dubi, A. and Hatziolos, M.E. 2007. Coral reefs under rapid climate change and ocean acidification. Science 318: 1737-1742.

Jury, C.P., Whitehead, R.F. and Szmant, A.M. 2010. Effects of variations in carbonate chemistry on the calcification rates of Madracis auretenra (= Madracis mirabilis sensu Wells, 1973): bicarbonate concentrations best predict calcification rates. Global Change Biology: 10.1111/j.1365-2486.2009.02057.x.

Langdon, C. and Atkinson, M.J. 2005. Effect of elevated pCO2 on photosynthesis and calcification of corals and interactions with seasonal change in temperature, irradiance and nutrient enrichment. Journal of Geophysical Research 110: 1-54.

Langdon, C., Broecker, W.S., Hammond, D.E., Glenn, E., Fitzsimmons, K., Nelson, S.G., Peng, T.-S., Hajdas, I. and Bonani, G. 2003. Effect of elevated CO2 on the community metabolism of an experimental coral reef. Global Biogeochemical Cycles 17: 10.1029/2002GB001941.

Marubini, F., Ferrier-Pages, C., Furla, P. and Allemand, D. 2008. Coral calcification responds to seawater acidification: a working hypothesis towards a physiological mechanism. Coral Reefs 27: 491-499.

Reynaud, S., Leclercq, N., Romaine-Lioud, S., Ferrier-Pages, C., Jaubert, J. and Gattuso, J.-P. 2003. Interacting effects of CO2 partial pressure and temperature on photosynthesis and calcification in a scleractinian coral. Global Change Biology 9: 1660-1668.

Ries, J., Cohen, A. and McCorkle, D. 2008. Marine biocalcifiers exhibit mixed responses to CO2-induced ocean acidification. In: 11th International Coral Reef Symposium, Fort Lauderdale, Florida USA, 7-11 July 2008, p. 229.

Schneider, K. and Erez, J. 2006. The effect of carbonate chemistry on calcification and photosynthesis in the hermatypic coral Acropora eurystoma. Limnology and Oceanography 51: 1284-1293.

Wood, H.L., Spicer, J.I. and Widdicombe, S. 2008. Ocean acidification may increase calcification rates, but at a cost. Proceedings of the Royal Society B 275: 1767-1773.

Reviewed 26 May 2010