The Starfish Population Explosion
“Awake!” correspondent in Hawaii
FOR decades a starfish called “crown of thorns” was rarely seen. In the 1920’s an extensive survey conducted along Australia’s Great Barrier Reef found only one specimen. But today South Pacific waters abound with them. A population explosion in starfishdom!
This has caused problems for man. Coral reefs are being destroyed by the teeming starfish. An odd thing about it is that the reef-building tiny coral polyps are natural enemies of the starfish, since they devour its free-swimming larvae. But now the tables have turned.
Swarms of 10,000 to 20,000 crown-of-thorns starfish have devastated much of Australia’s Great Barrier Reef, which covers over 250 miles. There is damage to reefs at other islands too, such as Guam and Fiji. And some 20,000 giant starfish have been found about 1,300 yards away from Hawaii’s offshore coral reef.
Why the starfish population explosion? A marine imbalance, concerning which one authority stated: “It is an incredible story, never before known in the history of marine biology.”
The Crown-of-Thorns Starfish
The starfish is built around a central point like a wheel, many of them having five arms. But the crown-of-thorns variety usually has sixteen arms! And as its name indicates, its two-foot-wide topside is covered with long, poisonous thorns.
From a central mouth on the starfish’s underside radiate sixteen grooves, one in each arm. Lining these grooves are rows of slender tubes. They are called “tube feet.” At the end of each tube foot is a suction cup, and there are hundreds of these on each arm.
Most helpful to Mr. Starfish when he is hungry, these feet enable him to grip tightly, with a force equal to about twenty-five pounds to the square inch. They can pull open even large oysters, to feed upon them. When the starfish dines on coral, it simply folds its many arms over its potential meal, and gets a good foothold. Then an amazing thing happens: The starfish turns its billowy stomach inside out through its mouth, spreads it over its victim like a collapsed parachute and pours digestive juices on the coral—and the meal is enjoyed.
As with other starfish, the crown of thorns is a remarkable creature. For one thing, it can grow new arms if old ones are broken off. In fact, an entire animal can grow from only one arm that has a portion of its central disk.
Why the Population Explosion?
But what is the cause of the imbalance that has led to the starfish population explosion? There is some uncertainty. A theory that seems valid for Australia is this: One of the few creatures that preys on the crown-of-thorns starfish, the giant triton shell, is dwindling in numbers. This beautiful, giant mollusk, commonly called the conch shell, sometimes grows to more than one foot in length. When a giant triton overtakes a starfish, it proceeds to devour it. Sometime after eating the spine-covered starfish the triton ejects the thorns.
But why are there fewer starfish-eating tritons? Australian marine experts, studying the problem, believe that the demands of tourists and collectors of the shell of the giant triton have brought about the situation. The experts reached this conclusion because they found that the worst damage from coral-eating starfish was usually on the inner side of the barrier reef, the side more accessible to humans. Dr. Robert Endean of the University of Queensland has calculated that shell collectors robbed the Great Barrier Reef of at least 100,000 tritons between 1949-1959.
Once again, as has been the case in other imbalances in the past, man seems to be behind this marine phenomenon. Five theories based on much circumstantial evidence have been advanced by top scientists investigating the matter under the auspices of the United States Department of Interior. These findings indicate that man has upset the reef’s delicate ecological balance by more means than one. They are: (1) Excessive radiation from atomic testing; (2) too much collecting of the rare triton shell; (3) too much dredging; (4) DDT pollution and (5) fish dynamiting.
When man blasts channels or he dynamites for fish, he can kill coral. And when a reef of living coral is killed by man, there are no polyps to eat starfish larvae; further the larvae now settle down in the dead reef and grow up in safety. One authority reports that great numbers of starfish in Guam and Ponape “were first discovered near blasting or dredging sites.” Thus the problem has many earmarks of being man-made.
Coping with the Problem
Some Australian plans for controlling the starfish population include large-scale collecting of this living pincushion and the importing of triton shells, releasing them to feed upon starfish. Also under consideration is how the triton can be propagated in large numbers. At present there is a ban on the taking of the triton shell from the Great Barrier Reef.
Some authorities have urged Australia to institute an emergency program of starfish extermination. But “we will not rush into any schemes or ideas for destroying the crown of thorns starfish,” said Nigel H. Bowen, federal Minister for Education and Science, “until we can assess, appreciate and understand the real nature of the problem.”
There is wisdom in gaining sufficient knowledge before acting. For example, years ago oyster fishermen, enraged by the eating habits of the starfish, used to take every starfish they caught and tear it into many pieces, throwing them back into the sea. Little did they realize they were only increasing their problem, for from a little torn-off arm a big starfish can grow!
In many news reports the starfish is depicted as the villain. But is it? May this not simply be another example showing what man has done to the earth and the consequent bad effect to himself?
It is true that the destruction of reefs has resulted in loss of a source of seafood for some islanders. But the fact of the matter is that the earth is constantly undergoing changes that affect man’s sources of supply of food. Yet there is plenty of food on this earth. It is not the starfish that is causing people to go hungry. Rather it is the political divisions set up by men, as well as their greedy commercialism.
Man needs to learn to live with his environment, to cooperate with it and to make adjustments in his activity, as changes over which he has no control require it. Then the starfish will no longer be viewed as a villain but as the remarkable creature it is.