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December 6, 2004

Some Tropical Corals Can't Take the Heat

Smith College Study Shows Some Reefs May Disappear if Sea Surface Continues to Warm

NORTHAMPTON, Mass.—Smith College researchers identified one biochemical mechanism that gives some species of coral an inherent defense against warming sea waters, and leaves others vulnerable. This finding provides insight into the death of large expanses of coral during the most recent El Niño event, and suggests loss in this rich ecosystem if marine sea-surface temperature fluctuations continue.

The study, published in the latest issue of Marine Ecology Progress Series, identifies different levels of heat shock proteins—proteins that function as the first line of defense against environmental stress in organisms from bacteria to humans—as the factor that makes corals either resilient or vulnerable to temperature change.

Temperature anomalies associated with the 1998 El Niño killed portions of many coral reefs globally, endangering a habitat providing high levels of biodiversity and buffering from erosion shorelines in areas such as southern Florida, Hawaii and the Caribbean. The loss of coral reefs could decimate livelihoods gained from fishing and tourism.

“Those species that are not resilient to temperature fluctuations are likely to be lost as warming trends are expected to continue,” said Paulette Peckol, Louise C. Harrington Professor of Biological Sciences, and a study author. “That could have a drastic impact in tropical regions of the world.”

Smith College researchers studied heat shock protein levels in two common species of coral, called Agaricia tenuifolia and Agaricia agaricites, taken from reefs off the coast of Belize. To examine the temperature tolerance of each species, corals were exposed to water that was the typical tropical temperature, 82 degrees Fahrenheit (28 degrees Celsius), and to water that was typical of El Niño hotspots, 93 degrees Fahrenheit (34 degrees Celsius).

Agaricia agaricites registered twice the amount of heat shock protein as Agaricia tenuifolia at the lower temperature, and six times the amount of heat shock protein when the temperature increased, according to the study.

Because of its inability to produce enough heat shock protein, the coral species Agaricia tenuifolia cannot stabilize its cells to the temperature change and is more vulnerable to environmental stress, the researchers said. In the Belize study area,
95 percent of Agaricia tenuifolia died during the recent El Niño, as opposed to18 percent of Agaricia agaricites.

In addition to Peckol, researchers included Stylianos Scordilis, professor of biological sciences; H. Allen Curran, William R. Kenan, Jr., Professor of Geology; Martha L. Robbart, who received a bachelor’s and master’s degree in biological sciences from Smith; and Jocelyn Brown-Saracino, who received her bachelor’s in 2004. The study was supported by the Blakeslee Fund for Genetics Research at Smith College, a Culpeper Foundation grant, the Smith College Summer Science Program and the B. Elizabeth Horner Fund.

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