Crown-of-thorns Starfish

The crown-of-thorns starfish (Acanthaster planci complex) is a large, many-armed sea star covered in venomous spines that feeds on coral. Population outbreaks have destroyed large areas of reef in the Indo-Pacific.

🧬 Field Guide Specimen: Open Crown-of-thorns Starfish in the CRV Science Field Guide to log the specimen, see its place among the Deuterostomia lineages in the Cladogram Explorer, and test your recall in the Red List conservation game.

A single starfish eats several square meters of coral a year, and outbreaks of millions of starfish can strip a reef. One analysis attributed about 40 percent of the coral cover lost on the Great Barrier Reef between 1985 and 2012 to this animal. Outbreaks may be fueled by nutrient runoff that boosts the phytoplankton fed on by the starfish larvae.

The spines are venomous and can inflict painful wounds. Adults have up to about 20 arms and move over the reef at night.

Divers inject starfish with vinegar or bile salts to kill them, and an underwater robot guided by machine learning has been tested. Reducing nutrient runoff may help prevent outbreaks. See Coral bleaching.

• Coral bleaching — other stresses on reefs
• Staghorn Coral — a reef coral