Marine biologists discovered the crown of thorns starfish in Australia, where it lives around the Great Barrier Reef. Its habitat ranges throughout all the tropical oceans and divers have found them everywhere from the Red Sea to the Pacific coast of Panama and the Indian Ocean.
The crown of thorns lives among colonies of coral on coral reefs made of hundreds of thousands of small polyps. Polyps are the living tissue of coral, feeding mostly on algae and plankton. Supporting them is the hard skeleton of dead coral, which is the backbone of the reef.
Many creatures cannot eat polyps easily because they are only a thin layer of living tissue. They can also withdraw into a hard exoskeleton that acts like a protective cup. The crown of thorns starfish has a specially developed system for ingesting the polyps. It climbs on top of the living coral and spreads its stomach out underneath its body with its many flexible arms. The digestive juices from the stomach are able to gather the living cells, leaving the white coral skeleton behind.
The crown of thorns starfish has caused controversy in the last 20 years because of its rate of coral consumption and the slow growth of coral reefs. An adult can eat 65 square feet of living coral each year. Normally they live in very small numbers, according to the Great Barrier Reef Marine Park Authority. They help keep the coral population under control, making room for new reefs to form. In 1979 and again in 1996 marine biologists found huge starfish colonies on one reef and began population control experiments off the coast of Australia.
There are two hypotheses for the cause of outbreaks of crowns of thorns starfish, according to research by the Australian Institute of Marine Science. One school of thought is the level of nutrients in the ocean rise according to rainfall and water flow every 17 years, causing a dramatic rise in the number of starfish. The second theory involves the natural predator of the starfish, the giant triton. This is a large mollusk that grows a beautiful shell that people love to take home. Collecting has lowered the population of the main predator of the crown of thorns starfish.
