The fossilized corals they studied - belonging to the genus Coelosmilia, which were commonly found during the Cretaceous period - had calcite skeletons, a form of calcium carbonate less susceptible to the corrosive effects of a lower pH (as opposed to aragonite). "We now have many different arguments to prove that these corals were actually made originally out of calcite—and not just aragonite that was transformed after the coral died and become fossilized ... There was great biological variability among the corals, and some of them adjusted perfectly to the prevailing geochemical situation," said Stolarski.If calcite skeletons were more effective at dealing with an increasingly acidic ocean, why were there still so many aragonite skeletons? According to Stephen Cairns, a research zoologist at the Smithsonian's National Museum of Natural History, it may be because corals evolved the ability to switch their skeletons from one form to the other: "This study has opened the door to the possibility that coral skeletons can potentially change back and forth from aragonite to calcite."
Stolarski stresses the importance of maintaining coral diversity to ensure the fragile organisms' long-term survival. "If we completely eliminate some families or groups of corals, we may lose the very corals that would be able to adjust to changing environments in the future," he cautioned. Assuming modern corals will be able to display the same (or similar) resistance mechanisms as their ancient forebears - still a big "if" at this point - there may yet be hope for them.
Via ::National Geographic News: Corals May Have Defense Against Global Warming (news website)
See also: ::Never Mind Future Temperature Increases: CO2 Emissions Deserve EPA's Attention NOW, ::Corals Engage in Fisticuffs with Global Warming
Image courtesy of National Geographic