Starfish threaten Australia's Great Barrier Reef - and tourism. Scientists debate cause, remedy for outbreak of Crown of Thorns
Great Barrier Reef, off Townsville, Australia — Seen from the air, the Great Barrier Reef still looks every bit the eighth wonder of the world. The massive chain of 3,000 coral reefs stretches 2,000 miles along the eastern coast of Australia. But dive beneath the shimmering Pacific and the picture changes. Almost one-third of the Great Barrier Reef has been attacked, and some major reefs 95 percent destroyed. Brightly colored coral gardens are now drab grey rocks with mottled khaki coats of algae.
The culprit: a venomous, coral-eating starfish known as the Crown of Thorns.
Portions of the reef have been swept by two infestations of the starfish. The first outbreak began in the early 1960s. The second started in 1979; today hundreds of thousands of the spiny-backed creatures are munching their way south.
The infestation is not limited to Australia's Great Barrier Reef, although it has not touched the Caribbean or the Atlantic. During the last 25 years, the Crown of Thorns have devoured coral off the coasts of Panama, Japan, Thailand, Malaysia, the Philippines, India, Indonesia, Kenya, almost every island nation in the Pacific, and in the Red Sea.
(The starfish don't eat the reef rock but the jelly-like coral polyps inside. These tiny creatures secrete limestone, which builds the reef.)
For the growing populations of developing nations around the world, the impact of the Crown of Thorns can be severe. The loss of coral means less food. Living coral is the basis of an ecosystem for thousands of marine organisms, including fish. Coral reefs are already under assault from human activities such as pollution and dynamite fishing. The starfish exacerbate the problem.
In every nation, coral reefs attract tourist dollars. In Townsville, Australia, dive operators now complain they must travel further and further to find coral to satisfy visiting skin divers. Some overseas tourist operators are reportedly advising visitors to stay away from resorts near affected reefs.
Several nations have tried to stop the voracious starfish but victories are minor. Often, there are so many starfish that only small patches of reef can be saved. Teams of divers must inject each starfish with poison or remove them by hand for months on end.
Leon Zann, coordinator of the Crown of Thorns research program for the Great Barrier Reef Marine Park Authority (GBRMPA), told scientists at a coral reef symposium in Townsville recently that pilot programs show hand control is ``futile.'' That kind of reef preservation would cost $5-$16 per starfish, with a final tab of ``hundreds of millions'' annually, he said. Scientists are putting up fences on a small test basis to keep the starfish off sections of the reef.
According to Dr. Zann, biological warfare appears to be the only solution. But ``before we put bugs in the water, even if there were a bug that kills the starfish, we have to be very sure those starfish outbreaks are an artifact of human intervention,'' he says.
Therein lies a debate in the scientific community that has raged for 20 years: Are the starfish part of a natural reef cycle or are they a pest that has gotten out of control because of human influence?
Many scientists believe that the infestations are like fires in a forest - a natural, recurring process that stimulates growth. But the second infestation has raised doubts.
If in the past, an infestation of this magnitude began every 15 years, the massive coral heads that take many decades to form would not exist today, says Robert Endean of the University of Queensland.
Research into overfishing, the possible decline of starfish predators, and human factors that could stimulate an outbreak will be the major thrust of GBRMPA efforts in the future, Zann says.
``It's a start,'' says Dr. Endean. Since 1969, he has publicly criticized GBRMPA for taking the politically (and financially) expedient view that the starfish are a passing natural phenomenon.
University of Miami biologist Peter Glynn is doing research in the Pacific on how damsel fish defend coral from Crown of Thorns starfish. He believes that infestations occur naturally every century or two, but humans trigger more frequent outbreaks. He subscribes to the Birkeland ``nutrient run-off'' hypothesis.
Charles Birkeland of the University of Guam noticed in 1981 that starfish outbreaks occur roughly three years after areas have heavy rainfall. He suggests that soil nutrients washed to sea, perhaps because of bad land management, have created ``algae blooms.'' These provide a rich menu for starfish larvae. Subsequent experiments by other scientists would seem to refute this theory, but Mr. Birkeland insists those experiments contain flaws.
The ``coral killers'' are chewing a path toward the Whitsunday Islands, one of Australia's most popular resort areas. ``In two years it will be affected and all hell will break out because these are the big boys in tourism development,'' Endean says.
Still, Zann has his fingers crossed. During the last invasion, the starfish stopped just short of the Whitsunday reefs. ``We're hoping it happens again. If they do go further, we're in heaps of strife.''