Johns Hopkins University
Fall/Winter 2006
Vol. 4, No. 1


A "Broken" Approach to Community Policing

Science's Coming Explosion

Fellows Marry Theory with Practice

Independent Inquiries

> A Skeletal Switch for Coral as Seawater Changes

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A Skeletal Switch for Coral as Seawater Changes

Leopards may not be able to change their spots, but corals can change their skeletons, building them out of different minerals depending on the chemical composition of the seawater around them.

That’s the startling conclusion drawn by Krieger School postdoctoral fellow Justin Ries, PhD ’05, and colleagues, who reported their findings in the July issue of the journal Geology. Ries collaborated on the research with his dissertation advisors, Steven M. Stanley (now of the University of Hawaii) and Lawrence A. Hardie, professor in the Krieger School’s Morton K. Blaustein Department of Earth and Planetary Sciences.

Ries and his collaborators say this is the first known case of an animal altering the composition of its skeleton in response to change in its physical environment. The aquatic animal’s sensitivity to such changes poses questions about its evolutionary history, as well as the future of the ecologically important coral reefs that it builds, Ries says, especially at a time when seawater is changing in response to global warming and the buildup of carbon dioxide in the atmosphere.

Reefs are large underwater structures of coral skeletons, made from calcium carbonate secreted by generation after generation of tiny coral polyps over sometimes millions of years of coral growth in the same location. Growing different corals in 10-gallon tanks, each with different “recipes” of seawater, over two months, Ries showed that corals can switch from using aragonite to another mineral, calcite, in making the calcium carbonate. They make that switch in response to decreases in the ratio of magnesium to calcium in seawater, Ries says. That ratio has changed dramatically over geologic time.

“This is intriguing because, until now, it was generally believed that the skeletal composition of corals was fixed,” he says.

His team’s experiments have significance with respect to global warming and ocean acidification, Ries says, because they reveal that although corals can adapt mineralogically to altered seawater chemistry, doing so slowed the corals’ rate of growth by nearly 65 percent.

Says Reis, “This provides us with further evidence that corals are extremely sensitive to rapid environmental change, such as global warming.”