The crown-of-thorns starfish (COTS) is a naturally occurring corallivore on coral reefs. They feed on hard, or stony, coral polyps. Covered in long poisonous spines, it is one of the largest starfish in the world. These starfish are generally 25-35 cm in diameter, but they can be as large as 80 cm.
In normal numbers on healthy coral reefs, COTS are an important part of the ecosystem. They tend to eat the faster growing corals which gives the slower growing species a chance to catch up, enhancing the coral diversity of our reefs. However, when the coral-eating starfish appear in outbreak proportions, the impact on coral reefs can be disastrous.
However, when branching coral cover is low due to overabundance of COTS or environmental conditions, COTS may eat other corals such as Porites or foliose corals. In addition to hard corals, COTS may also eat sponges, soft corals, algae, and encrusting organisms.