Marine Biology: Plague in the Sea

Few creatures are more aptly named. The crown-of-thorns, a large, reddish brown sea dweller, has as many as 21 arms, all covered with venomous spines that can temporarily paralyze a swimmer and provoke fits of vomiting. Known to biologists as Acanthaster planci, this sinister-looking, 2-ft.-wide starfish is an even greater menace to some of its tiny aquatic neighbors. It likes nothing better than to feed on the living coral reefs where it makes its home.

Lately its appetite has become alarming. Once a relatively rare nocturnal predator, the crown-of-thorns suddenly began proliferating in the South Pacific a decade ago. Since then it has laid waste to 100 sq. mi. of Australia’s Great Barrier Reef, the world’s largest and most impressive collection of underwater coral formations. It has also destroyed nearly 22 miles of Guam’s coral barrier. Marine biologists report similar starfish damage off Saipan, Fiji and the western Solomons. In only five years, says Oceanographer R. D. Gaul of San Diego’s Westinghouse Ocean Research Laboratory, the starfish can destroy a coral atoll that may have taken thousands of years to form.

Baffling Phenomenon. Acanthaster’s ravages not only occur quickly but are long-lasting. After stretching itself over the coral, the crown-of-thorns quickly digests the simple organisms that constitute the tough outer layer of the reef. Structurally weakened, the remaining skeletons are easily eroded by the ocean’s waves. Once the coral barriers are breached, the islands that they surround are no longer protected from the pounding of the open sea. Because the reefs are vital to the spawning and feeding of much undersea life, the process can also destroy fertile fishing grounds almost overnight.

The Acanthaster plague baffles scientists. It could be a periodic natural phenomenon; many species mysteriously multiply for a time, then inexplicably decline in number. A more probable explanation is that man has upset the reefs delicate ecological balance. By relentlessly hunting for a rare trumpet-shaped mollusk called the giant triton, some scientists say, shell collectors have taken a devastating toll of one of the crown-of-thorns’ few natural enemies. Other scientists speculate that the imbalance may have been caused by dredging and underwater blasting, lingering pesticides or even radioactive fallout.

To control the crown-of-thorns, some scientists suggest repopulating the reefs with tritons, which are now protected by law in Queensland, Australia. Others propose spreading lime on the ocean floor, a technique that has already been used with moderate success to protect Long Island Sound’s oyster beds from the common American starfish, Asterias forbesi. A Japanese scientist has even advised stringing wire around coral reefs to repel the starfish with a low-voltage electric shock.

None of these tactics is guaranteed to curb the tough, durable crown-of-thorns. Australian researchers are pressing hard to find better answers. So, too, are 40 marine biologists and divers from San Diego’s Westinghouse Lab who fanned out across the Pacific this summer in an expedition sponsored by the U.S. Government. Unless the crown-of-thorns is restrained, many more miles of coral in the Pacific and other seas will be ravaged by the spreading starfish.