Distribution

Coral reefs of the Indo-Pacific, including the Red Sea.

Biology

Adult animals have a diameter of between 25 and 40 cm, but they can grow larger. 8–21 arms equipped with 4- to 5-cm-long sharp spines made of calcium carbonate. These spines are surrounded by a glandular integument that tears when the spine penetrates the skin and parts of which may remain in the wound.

Colouring very variable, blue-purple (Thailand, Maldives), fawn/grey/red (Great Barrier Reef, Australia) or green/red (Hawaii).

Crown-of-thorns live in coral reefs, where they avoid places where they will be exposed to the waves. They are found at depths of up to 65 m. Cryptic way of life. They feed chiefly on hard corals, but also soft corals, algae and gorgonians. They only eat the coral polyps, which they do by extruding their stomach onto the coral and digesting the polyps outside their body.

Normally the population density of crown-of-thorns is quite low. However, for reasons that are still not clear, from time to time there are sudden mass occurrences of these starfish, which subsequently represent a serious threat to the existing coral reefs. Such outbreaks are known to occur in Japan (Ryukyu Islands), Micronesia, Samoa, Fiji and in particular the Great Barrier Reef on the east coast of Australia. On the Great Barrier Reef two series of outbreaks of crown-of-thorns starfish have been recorded over the last 25 years; the first series occurred between 1962 and 1977, whilst the second, which is still ongoing, began towards the end of 1979. This latter outbreak has already led to extensive destruction of the reef.

Risk

Accidents are most likely in regions where there are outbreaks of these starfish and generally occur when the victim treads on or touches an animal. Reactions to the venom are generally local in nature (strong burning pain), rarely also systemic. Development of granulomas possible. The spines may break off and remain stuck in the wound. Shiomi et al. (1990) detected a potent liver toxin in the venom of Acanthaster planci when tested in mice. Lin et al. (2008) describe elevated liver enzymes after a puncture wound in a young patient.

Treatment

Symptomatic. Primarily prevention and treatment of infections. If broken-off spines stuck in the wound cannot be removed with forceps, it is better to wait until they come out spontaneously. This can be aided with the use of 2% salicylic acid cream, which softens the skin.

Literature (biological)

Moran 1990, Reichelt et al. 1990, Mebs 1989a, Exton 1987, Williamson et al. 1996, Mebs 1995a

Acanthaster biology

History of outbreaks