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Monday, August 11, 2008

Violent World of Corals Is Facing New Dangers

Beautifull abloom with a wealth of life unsurpassed for total beauty, coral reefs seem to exist in a state of dreamy tranquillity. Not so.

The reef is in truth a realm of violent struggle and constant problems. Coral colonies wage unrelenting chemical warfare on each other, their polyps stinging, dissolving and poisoning each other. Bigger reef creatures savage large chunks of colonies and fill the water with toxins. Sooner or later, an irresistible force like a hurricane or a change in sea level lays waste the whole teeming ecosystem and the corals must rebuild.

But rebuild they do, and this resilience is at the heart of a dispute among marine biologists over the contribution of human activity to the stresses on coral ecosystems.

One school of thought holds that corals worldwide are now in serious peril because of human assaults like global warming, overfishing, pollution and physical destruction of reefs by fishermen and tourists.

An opposing school holds that while some reefs are indeed in big trouble, many others remain pristine and even the damaged ones have adapted in the past to natural forces at least as destructive as human activity.

Any serious threat to corals would be an ecological tragedy. The biological diversity of coral reefs compares with that of tropical forests. Reefs themselves, built from the calcified skeletons of polyps, are the largest structures created by life. The many strange toxins evolved by reef denizens for their biological warfare hold considerable promise as treatments for various human diseases.

For all these reasons, there has been a heightening of scientific interest in corals of late, including an outpouring of research on coral ecology and chemistry.

Coral colonies, each composed of numerous tiny, tentacled polyps, take the forms of trees, shrubs, fans, plates and huge boulders. The phantasmagoria of shapes creates a habitat for other marine creatures like fish, lobsters, sponges, mollusks, octopuses and sea anemones.

Competition with a quarter given is the rule in this interdependent but mutually hostile Planet. When polyps in one colony come face to face with another in a constant competition for scarce space, they expand their bodies to engulf their rivals and exude digestive juices that turn the competitors to jelly.

As a countermeasure, polyps in the second colony grow "sweeper tentacles" studded with special stinging organelles that "zap the neighbors," says Dr. Judith Lang, a reef ecologist at the Texas Memorial Museum at the University of Texas.

Still other polyps enshroud their enemies in a sticky mucus that dissolves the tissues. Combat with toxins is also thought to be a common mode of warfare, though the toxins have proved hard to pin down in actual use.

Coral reefs may be one of the most naturally poisonous environments on earth.

Because of this great potential, the reefs have recently become prime prospecting grounds. Many potentially useful compounds have been discovered and are now undergoing further testing, said Dr. David J. Newman, a chemist in the National Cancer Institute's Natural Products Branch. The center has been collecting about 1,000 samples of coral-reef organisms a year for the last five years. The prospecting effort is still young, the journey to market for any drug derived from natural sources typically takes 5 to 15 years.

In nature, the coral toxins may play an indirect but key role in the reef ecosystems' resilience in the face of disturbance. Dr. Robert Endean and Dr. Ann Cameron of the University of Queensland in Australia, who has long studied the Great Barrier Reef, postulate that extensive boulder-like coral colonies have been able to exist continuously for hundreds and even thousands of years because they are so successful in using toxins to escape from predators.

Uploaded By: WILLIAM K. STEVENS, February 16, 1993

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