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Crown of Thorns Starfish and Coral Reefs The crown of thorns starfish, Acanthaster Tlanci, is large, twenty-five tothirty-five centimeters in diameter, and has seven to twenty-one arms that are covered in spines. It feeds primarily on coral and is found from the Indian Ocean to the west coast of Central America, usually at quite low population densities.Since the mid-1950s, population outbreaks at densities four to six times greaterthan normal have occurred at the same time in places such as Hawaii, Tahiti,Panama, and the Great Barrier Reef. The result has often been the loss of a fifty percent to nearly one hundred percent of the coral cover over large areas. A single Acanthaster can consume five to six square meters of coral polyps per year, and dense populations can destroy up to six square kilometers per year and move on rapidly. Acanthasters show a preference for branching corals, especially Acroporids. After an outbreak in a particular area, it is common to find that Acroporids have been selectively removed, leaving a mosaic of living and dead corals. In places where Acroporids previously dominated the community devastation can be almost complete, and local areas of reefs have collapsed. Areas of dead coral are usually colonized rapidly by algae and often are later colonized by sponges and soft corals. Increases in abundance of plant-eating fish and decreases in abundance of coral-feeding fish accompany these changes.Coral larvae settle among the algae and eventually establish flourishing coral colonies. In ten to fifteen years the reefs often return to about the same percentage of coral cover as before. Development of a four-species diversity takes about twenty years. Two schools of thought exist concerning the cause of these outbreaks. One group holds that they are natural phenomena that have occurred many times in the past, citing old mens recollections of earlier outbreaks and evidence from traditional c