How does rising atmospheric CO2 affect marine organisms?

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Calcification Response of a West Atlantic Coral to Global Warming
Carricart-Ganivet, J.P. 2004. Sea surface temperature and the growth of the West Atlantic reef-building coral Montastraea annularis. Journal of Experimental Marine Biology and Ecology 302: 249-260.

What was done
Following in the footsteps of Lough and Barnes (1997, 2000), who studied massive Porites corals in the Indo-Pacific, the author developed relationships between coral calcification rate and annual average sea surface temperature (SST) based on data collected from colonies of the reef-building coral Montastraea annularis at twelve localities in the Gulf of Mexico and the Caribbean Sea.

What was learned
In the words of the author, "calcification rate in the Gulf of Mexico increased 0.55 g cm-2 year-1 for each 1C increase, while, in the Caribbean Sea, it increased 0.58 g cm-2 year-1 for each 1C increase." Although the data from the two regions yielded slopes that were not significantly different from each other - producing a slope of 0.57 g cm-2 year-1 when they were pooled (a result nearly twice as great as that obtained by Lough and Barnes for Porites corals) - Carricart-Ganivet notes that the significantly different intercepts of the two relationships "indicated calcification would cease in corals from the Gulf of Mexico at 23.7 and at 25.5C in corals from the Caribbean Sea."

Further pooling these data "with those of M. annularis and M. faveolata, growing up to 10 m depth in Carrie Bow Cay, Belize, reported by Graus and Macintyre (1982), those of Dodge and Brass (1982) from all the reefs they studied at St. Croix, US Virgin Islands, and those of M. faveolata, growing up to 10 m depth in Curacao, Netherlands, Antilles, reported by Bosscher (1993)," Carricart-Ganivet reports he obtained a relationship of ~0.5 g cm-2 year-1 for each 1C increase in annual average SST.

What it means
Some scientists have predicted that rising atmospheric CO2 concentrations will lead to significant decreases in coral calcification rates (Kleypas et al., 1999; Caldeira and Wickett, 2003; Buddemeier et al., 2004), suggesting that many corals may actually be driven to extinction by this phenomenon. In fact, they claim that the historical increase in the air's CO2 content that has been experienced since the inception of the Industrial Revolution should have already had a significant negative impact on the calcification rates of most of earth's corals. However, Lough and Barnes have demonstrated that at the rate at which SSTs have risen concurrently, the positive effect of the increasing temperature has more than compensated for the negative effect of the rising atmospheric CO2 concentration. And now, Carricart-Ganivet has documented a positive effect of increasing temperature in two other coral species that is nearly twice as great as that found by Lough and Barnes.

Clearly, the doom-and-gloomers are going to have to re-think their position on the CO2 coral calcification catastrophe. Real-world data just don't support it.

Buddemeier, R.W., Lkeypas, J.A. and Aronson, R.B. 2004. Coral Reefs & Global Climate Change: Potential Contributions of Climate Change to Stresses on Coral Reef Ecosystems. The Pew Center on Global Climate Change, Arlington, VA, USA.

Caldeira, K. and Wickett, M.E. 2003. Anthropogenic carbon and ocean pH. Nature 425: 365.

Kleypas, J.A., Buddemeier, R.W., Archer, D., Gattuso, J.-P., Langdon, C. and Opdyke, B.N. 1999. Geochemical consequences of increased atmospheric carbon dioxide on coral reefs. Science 284: 118-120.

Lough, J.M. and Barnes, D.J. 1997. Several centuries of variation in skeletal extension, density and calcification in massive Porites colonies from the Great Barrier Reef: A proxy for seawater temperature and a background of variability against which to identify unnatural change. Journal of Experimental and Marine Biology and Ecology 211: 29-67.

Lough, J.M. and Barnes, D.J. 2000. Environmental controls on growth of the massive coral Porites. Journal of Experimental Marine Biology and Ecology 245: 225-243.

Reviewed 7 July 2004