The sea star, Acanthaster planci, widely but sparsely distributed throughout the tropical Indo-Pacific region, has experienced sudden local population explosions causing unprecedented damage to certain coral reefs of the Pacific. By devouring and killing hard corals en masse, this animal has created massive environmental upheavals as hordes advance systematically over reef surfaces reducing coral communities to dead rubble. In order to preserve Green Island (Australia), divers have been collecting for destruction as many as 375 individuals per day for more than 15 months. Nevertheless, the entire width of more than 1 mi of reef has been devastated. As new outbreaks occur, there is fear in Australia that this sea star, if unchecked, ultimately could destroy the entire Grea Barrier Reef and along with it the valuable marine community that it harbors. In 1966-1968 the writer discovered localized Acanthaster populations of very high density at Guam, Saipan, Koror, Fiji, and New Guinea. The problem is not only of considerable importance to the economy, health, and welfare of inhabitants of Pacific Islands, but elucidation of the factors permitting the phenomenal increase in numbers may help the understanding of apparent catastrophic events concerning coral reefs as indicated by the geologic record. The writer's ecologic studies of Acanthaster are guided by two hypotheses: (1) an unknown predator of the sea star has been removed from these reefs, possibly by man, and (2) a mutant, more venomous strain of A. planci evolved in the 1950s or 1960s. At present, the e is some evidence supporting both hypotheses.

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