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Chemical pollution in the sea and the crown-of-thorns starfish (Ancanthaster planci)

Author(s): Randall JE

Abstract

Within the last decade infestations of the crown-of-thorns starfish (Acanthaster planci) have been reported from the Great Barrier Reef, Guam and other Mariana Islands, Caroline Islands, Marshall Islands, Palau Islands, New Hebrides, Solomon Islands, Fiji Islands, Western Samoa, Cook Islands, Tahiti in the Society Islands, Molokai in the Hawaiian Islands, Philippine Islands, Taiwan, and Ceylon. The starfish have also been noted as common in Viet Nam, Tanzania, Tonga Islands, Gilbert Islands, Nauru, Papua, New Caledonia, Ko Khao (off Thailand), Wake, the Tuamotu Archipelago, and near Port Sudan, Red Sea. Within these areas the distribution of the starfish is spotty. Nearly all of the infestations are near centers of human population. Some authors believe these infestations are merely normal fluctuations of abundance that have gone unnoticed in the past. The magnitude of some of the starfish plagues, however, seems too great for this explanation. The crown-of-thorns has killed up to 90 percent or more of corals on some reefs that represent more than 1000 years of continuous development. Also the areas of infestation are too numerous, too widespread, and have occurred over too short a span of time to believe that each is the result of an independent natural cycle. It is postulated that chemical pollution, most likely in the form of chlorinated hydrocarbon pesticides such as DDT, is responsible for the increased populations of A. planci. The pollutant's effect probably takes place in the pelagic community. A higher level of the pollutant may be expected in the predaceous zooplankton that feed on the larval starfish than in the larvae themselves. A level of pesticide must exist which reduces the population of one or more predators relative to the number of starfish larvae. The localization of the infestations of A. planci is probably the result of the chance combination of many factors such as a successful spawning of the starfish, the correct temperature for development, and the transport of the larvae in a current system (a gyre is needed to maintain the population at the island or reef of origin) to a suitable inshore environment for settlement. The excessive populations of sea urchins (Strongylocentrotus) in the coastal waters of southern California may also be a comparable effect of chemical pollution.

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