The study was published last week in the Proceedings of the National Academy of Science and will be presented at the meeting of the American Society for Photobiology in Washington, D.C., today. The findings confirm a growing consensus, based on recent studies, that the gradual warming of the oceans is a major cause of coral reef bleaching. It turns out, however, that the higher temperatures aren't necessarily damaging the reef-building corals directly but instead are degrading the ability of symbiotic algae, upon which the survival of their hosts is dependent, to convert light into energy.
Symbiotic algae provide coral with color and nutrition.
Without it, reefs can survive for brief periods of time, but if the absence is prolonged they will perish. Providing habitat for 25 percent of all marine species, and protecting coastal areas from storm damage, coral reefs are considered one of the most important ecosystems on Earth. In field tests conducted in the Caribbean and replicated in the laboratory, the researchers pioneered the use of a technique known as pulse-amplitude modulation fluorometry. The technique allows scientists to determine the efficiency of light used by the symbiotic algae, an improvement over other methods of measuring the metabolic activity. During the summer of 1997, seawater temperatures in the Florida Keys remained above normal for weeks on end.