Crown of thorns sea star, COT

Scientific name : Acanthaster planci

Large sea star (up to 50 cm diameter), with 9-23 arms, highly variable colour (grey to purple, to orange). Covered with long, acute spines. Normally found in back reef and reef front. It feeds on hard corals, whose soft tissues are digested on the place, by the stomach evaginated through the mouth. It leaves behind only the bare skeleton of the coral, perfectly white. With its food hard coral. It has venomous spines, giving very painful stings. Only few animals can feed on it: the triton shell Charonia tritonis, The napoleon wrasse (Cheilinus undulatus), few large trigger fishes (Balistoides viridescens). Even if the colour is variable, the size and spines make it unique. A crown of thorn starfish (often shortened as COT) can destroy everyday 1 square meter of coral. When the populations of this echinoderm, normally rare, increase in number, they can seriously damage the reef. Acanthaster blooms have been studied in many Indo-Pacific areas. Often these blooms have been put in relation with the local extintion of the natural predators (like the triton shell or the napoleon wrasse), but actually all those predators, eating few starfishes in a week, could never control a demografic bloom. The triggering factor should be looked upon in the larval stage, in some event drastically reducing the early mortality (all sea stars produce hundreds of thousands of larvae). Anyway, human induced environmental changes can be somehow at the origin of the phenomenon.