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  National Geographic 4 Oct 07
Corals May Have Defense Against Global Warming
Helen Scales for National Geographic News

Ancient corals may have been more adaptable to changing ocean chemistry than previously thought, a new study shows.

The findings may offer hope that modern corals can adapt as global warming causes seas to become more acidic.

These fossil corals in diverse reef communities adjusted to an acidic environment by altering the way they built their chalky skeletons.

Modern hard corals—known as scleractinians—form reefs of thousands of tiny skeletons made from a calcium carbonate called aragonite.

Aragonite is susceptible to the corrosive effects of acidic oceans, which today has become a byproduct of a build-up of carbon dioxide in the atmosphere.

"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," said study co-author Jaroslaw Stolarski, a paleontologist from the Institute of Paleobiology at the Polish Academy of Sciences.

Curious Coral

The calcite skeletons were identified using several tests. Scientists inspected the microscopic structure of the skeleton and detected a high ratio of magnesium to calcium—a telltale fingerprint of calcite, not aragonite.

The fossil corals look like two-inch-long (five-centimeter-long) sea anemones nestled in porcelain egg cups. They belonged to the genus Coelosmilia, which existed during the Cretaceous period about 70 million years ago.

The Cretaceous oceans had a chemistry different than today, with much less of the metal ion magnesium and higher acidity.

"In the same environment there were coral neighbors, some with aragonitic skeletons, some with calcitic skeletons," Stolarski said.

"There was great biological variability among the corals, and some of them adjusted perfectly to the prevailing geochemical situation," he said.

Rachel Wood, a geologist from the University of Edinburgh, who was not involved in the study, said, "It begs the question: If having a calcite skeleton was so much better for life in such a corrosive sea, why aren't there more of them?"

The research will appear tomorrow in the journal Science.

Diversity Benefits

"This study has opened the door to the possibility that coral skeletons can potentially change back and forth from aragonite to calcite," said Stephen Cairns, research zoologist at the Smithsonian Institution's National Museum of Natural History in Washington, D.C.

"It suggests that animals and plants in general are quite adaptable creatures, and even though Earth changes—sometimes dramatically, like [in the case of] a comet hitting and wiping out 90 percent of animal life—it is so resilient that a vestige still gets through."

Co-author Stolarski said that diversity may be the key to adaptability, even in today's corals, which are under threat from warming seas. (Related news: "Coral Reefs Vanishing Faster Than Rain Forests" [August 7, 2007].)

"We should be extremely careful about coral reefs today, because they can only adapt to these changing environments if they maintain their diversity."

"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."
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