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Crown-of-Thorns Starfish

(Acanthasteridae)

Snake Sea Stars Toxopneustidae Sea Urchins

There are only two species in the Crown-of-Thorns Starfish family, the Short-Spined Crown-of-Thorns Starfish (Acanthaster brevispinus) and the Common Crown-of-Thorns Starfish (Acanthaster planci), both of which are found in the Indo-Pacific region, but only one of which, the Common Crown-of-Thorns Starfish, is usually found at the dive sites around Koh Lanta.

Crown-of-Thorns Starfish are disc-shaped, multi-armed starfish, starting life with the typical 5 arms, but growing many more as it matures. Members of this family are densely covered in sharp, poisonous spines, have very flexible arms and large stomachs.

Crown-of-Thorns Starfish can be varying shades of blue, purple, red, brown or grey, with variably coloured spines, sometimes with yellow tips or orange.

1 species found on this page.

Common Crown-of-Thorns Sea Star

Acanthaster planci

The Common Crown-of-Thorns Sea Star is a large starfish, variably coloured red to purple, yellow and tan. There are 12 - 19 arms, covered with sharp, poisonous spines which can give a very painful sting.

The Common Crown-of-Thorns Sea Star diet includes coral polyps, and several individuals can consume large areas of coral within a very short period of time. This species can occasionally form very large colonies which can then devastate a coral reef.

Common Crown-of-Thorns Sea Star (Acanthaster planci) @ Koh Bida

Acanthaster planci @ Koh Bida

It is thought that one of the main causes of population explosion is excessive agricultural run-off, flooding areas with nitrates and nutrients. Dangerously large populations which threaten to destroy a coral reef can be controlled by injections of sodium bisulphate.

Common Crown-of-Thorns Sea Star (Acanthaster planci) @ Koh Bida

Common Crown-of-Thorns Sea Star @ Koh Bida

The Common Crown-of-Thorns Sea Star grows to 40 cm and can fully regenerate an individual adult from a severed limb. DNA analysis suggests that the Common Crown-of-Thorns Sea Star comprises 4 subspecies, each with its own distinctive range.

Find Out More: Marine Life References and Further Information

Diving with Crown-of-Thorns Starfish

Spot Crown-of-Thorns Starfish around Koh Lanta on one of our high season dive and snorkel trips.

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