Crown-of-thorns Starfish Populations
A. planci, commonly known as the crown-the-of- starfish, is large sea star that lives in tropical zones of the Red Sea, the Indian Ocean, and the Pacific Ocean. Covered with long. sharp spines that contain a neurotoxin that causes a stinging sensation in its prey, A. planci feeds on coral polyps, the animals that build reefs by secreting calcium carbonate to create hard skeletons that eventually become a reef. Until 1962 when large numbers were first seen off the coast of northeastern Australia, A. planci was considered rare. Soon after 1962, however, large numbers were observed on reefs throughout the Pacific and Indian oceans. With every population explosion, coral reefs were devastated. The starfish numbers declined in the mid-1970s, but a second, even worse population explosion occurred between 1979 and 1991, followed by a third that lasted through the 1990s and began waning only in 2008.
Scientists are uncertain why these outbreaks are occurring. On the one hand there is a possibility that this may be a natural part of reef ecology. Humans, after all, have been exploring marine environments only since the invention of diving gear during the Second World War. For all that today’s marine biologists know, crown-of-thorns outbreaks may have occurred on reefs ever since reets first appeared. Indeed, an analysis of bits of fossilized reef buried in the ocean floor indicates that the species has been devouring Great Barrier Reef coral for at least 8,000 years. More controversially, some scientists think this same study provides evidence for ancient outbreaks.This interpretation, if correct, would support the idea that periodic outbreaks-perhaps driven by the El Nino or fluctuations in temperature salinity and plankton levels-are normal. Furthermore, ecologists generally think that populations of species able to produce large numbers of offspring in short time are inherently unstable. The crown-of-thorns starfish is just such an animal. When conditions are right a single female can produce up to 60 million eggs each year.
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