State of the Reef Report 2004: Crown-of-thorns starfish

The crown-of-thorns starfish is one of only a few animals that feed on living coral tissue. The starfish is named for the dense covering of long, sharp spines on its upper surface. At low densities the crown-of-thorns starfish is a ‘normal’ part of the reef’s ecology. However, when the numbers of crown-of-thorns starfish on a reef increase to the point where they consume coral faster than it can grow, the starfish can dramatically reduce coral cover, resulting in a major disturbance to the whole system (see Environmental status - corals). This situation is commonly known as a crown-of-thorns starfish ‘outbreak’. Outbreaks of crown-of-thorns starfish have been a concern on the Great Barrier Reef for more than 40 years. Research suggests that the outbreak ‘trigger point’ is around 30 mature crown-of-thorns starfish per hectare of coral reef that has average levels of coral cover. Once crown-of-thorns starfish densities exceed this threshold, the population will begin to consume coral faster than it can grow and is considered to be an outbreak population