Crown-of-Thorns, Acanthaster planci

Crown-of-Thorns, Acanthaster planci. Underwater photograph taken in coastal waters off Isle Coronado, Baja California Sur, May 2023. Photograph courtesy of Dr. Tom Bartol, Carlsbad, California.

Phylogeny:  Crown-of-Thorns, Ancanthaster planci, is member of the Acanthasteridae Family of venomous starfish. It is also known as COTS and in Mexico as Corona de Espinas.

Morphology:  This spiny sea star boasts thirteen to sixteen arms with suckers that are relatively short compared to the large central disk. Their diameter ranges from 10 cm (3.9 inches) to 41 cm (16 inches). It’s adult form does not possess the five-fold symmetry that is common of most starfish, although juvenile forms have five-fold symmetry.

Habitat and Distribution:  The Crown-of-Thorns is found within the lower intertidal zone at depths up to (46 m) 150 feet. They prefer rocky reefs, particularly on offshore islands where rich coral and gorgonian growth occurs. They are distributed from the Central Gulf of California to Isla Clarion. Despite its affinity for a diet of coral, they are curiously absent from the Gulf’s only coral reef at Cabo Pulmo.

Reproduction:  The Crown-of-Thorns breeds through spawning in the summer months, via external fertilization.

Diet:  Coral polyps primarily make up the diet of this star fish, though they can live up to nine months without eating. One individual can eat through up to ten square meters of coral a year.

Ecosystem Interactions: The presence and density of the Crown-of-Thorns has implications on the health of coral reefs. The Commensal Shrimp, Periclimenes soror, lives among the sharp and venomous spines of the starfish.

Synonyms:  Acanthaster echinites, Acanthaster echinus, Acanthaster ellisi, Acanthaster ellisi pseudoplanci, Acanthaster pseudoplanci, Acanthaster solaris, Asterias echinites, Asterias echinus, Asterias planci, Asterias solaris, Echinaster ellisi, Echinaster solaris, Echinities solaris, and Stellonia echinites.