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Scleractinian Corals: To Hell (Decalcification) and Back
Fine, M. and Tchernov, D. 2007. Scleractinian coral species survive and recover from decalcification. Science 315: 1811.

Several researchers have suggested that many of earth's corals are destined to die, with some species even facing extinction, because of an hypothesized connection between the ongoing rise in the air's CO2 content and reduced rates of coral calcification driven by CO2-induced increases in oceanic acidity leading to decreases in the saturation state of aragonite, the principal mineral deposit of corals; and in light of this rampant speculation, Fine and Tchernov decided to examine "the ability of scleractinian corals to survive acidic conditions."

What was done
The two researchers grew 30 coral fragments from five coral colonies of the scleractinian Mediterranean species Oculina patagonica and Madracis pharencis within indoor flow-through systems under ambient Mediterranean seawater temperatures and photoperiod in water maintained at pH values of 7.3-7.6 (acidified) and 8.0-8.3 (ambient) for a period of 12 months.

What was learned
The Israeli scientists report that after one month in acidic conditions, there was an elongation of the coral polyps that was "followed by dissociation of the colony form and complete skeleton dissolution." However, they observed that "the polyps remained attached to the undissolved hard rocky substrate." In fact, they found that "the biomass of the solitary polyps under acidic conditions was three times as high [our italics] as the biomass of the polyps in the control colonies that continued to calcify and grow." In addition, they say that both "control and treatment fragments maintained their algal symbionts during the entire experiment, except for six fragments (10%) of O. patagonica that partially lost their symbionts (bleached) during July but recovered within 2 months." Last of all, they report that "after 12 months, when transferred back to ambient pH conditions, the experimental soft-bodied polyps calcified and reformed colonies."

What it means
After restating their major finding that "in the absence of conditions supporting skeleton building, both species maintained basic life functions as skeleton-less ecophenotypes," Fine and Tchernov conclude that "corals might survive large-scale environmental change, such as that expected for the following century." And why not? If they've done it before - as some have theorized (Stanley and Fautin, 2001; Stanley, 2003; Medina et al., 2006), and as Fine and Tchernov have now demonstrated can in truth be done - they likely have the capacity do it again.

Medina, M., Collins, A.G., Takaoka, T.L., Kuehl, J.V. and Boore, J.L. 2006. Naked corals: Skeleton loss in Scleractinia. Proceedings of the National Academy of Science U.S.A. 103: 9096-9100.

Stanley Jr., G.D. 2003. The evolution of modern corals and their early history. Earth Science Reviews 60: 195-225.

Stanley Jr., G.D. and Fautin, D.G. 2001. The origins of modern corals. Science 291: 1913-1914.

Reviewed 27 June 2007