October 1997

Vol. 12, No. 10     What's this?

Crumbling Coral

Mystery disease devastates tropical reefs

from the October, 1997 issue of Undercurrent  

Two coral researchers examined the reefs off Bonaire in January after divers noticed strange white lesions on star and brain corals. Dr. Thomas J. Goreau and Dr. James Cervino found something they had never seen before, huge patches of dead coral, bright white where the skeleton had been exposed after tissue had died; the skeleton itself was crumbling away.

“We were horrified,” said Dr. Goreau. “It looks like someone poured acid over the top of the coral. The skeleton itself is dissolved. I’ve been looking at reefs probably longer than anyone else alive and I’d never seen it before. It’s attacking at a speed and with a level of damage that is unprecedented.”

Rapid wasting disease, which can spread several inches across a coral head in a day, is all over the reefs of Bonaire. Since January, it has been spotted in Mexico, Aruba, Curaçao, Tobago, Grenada, and St. John’s, an area spanning 2,000 miles.

Rapid wasting disease is only one among many mysterious diseases attacking corals. In the last few years corals from the Caribbean to the Philippines have been quickly succumbing to diseases never before seen.

“We’re all stunned at the rapidity with which these new diseases are occurring,” said Dr. James W. Porter of the University of Georgia. “The problems are occurring at all depths and the number of species affected is increasing.”

Because of the newness of the diseases, recognizing whether a coral is healthy or sick can be difficult. For example, rapid wasting disease, which exposes a white, crumbling skeleton, is easily mistaken for anchor damage or parrotfish bites.

Some speculate that stresses like bleaching, sedimentation, and pollution have pushed corals to the point where they are no longer able to fend off diseases. However, Dr. Goreau says that “most diseases don’t correlate with each other or any known environmental stress. In Bonaire, rapid wasting disease is having a devastating impact, yet the reefs there are so clean.”

Others have suggested that erosion and dumping sewage and oil waste into the sea have brought new pathogens in contact with corals. For example, sea fan disease, discovered just four years ago, is widespread in the Caribbean. It’s caused by a highly opportunistic fungus that adheres to sediment; after being washed into the sea, it grows when it encounters a sea fan. “It’s a terrestrial organism that has crossed the land-sea barrier,” Dr. Harvell said.

Cures for sick corals are a long way off. While some have suggested applying antibiotics to the reefs, others caution about the unknown hazards of dispensing a drug that can destroy beneficial bacteria as well as harmful ones. Furthermore, the pathogens may not be bacteria at all.

Researchers have had the most luck treating black band disease by vacuuming off the diseased band of tissue. But that is impossible for quickly spreading diseases such as the white plague. In four months in 1995, it spread more than 100 miles, jumping from one to 17 species of corals.

Sometimes, however, no treatment can be the best cure. Once a disease is allowed to rage through an area, any healthy, resistant individuals left can rebuild a tougher population. However, Dr. Goreau says, sponges, coralline algae, and sea urchins are also succumbing to new illnesses, further threatening the health of reef communities.

Dr. Cervino is soliciting reports of new outbreaks of coral diseases from observers. His e-mail address is cnidaria@earthlink.net.

A version of this article, by Carol Kaesuk Yoon, originally appeared in the New York Times.