20. How do crown-of-thorns starfish eat?

The crown-of-thorns starfish is a specialist coral feeder although occasionally (particularly when corals are in short supply) it may feed on other organisms (eg. soft corals, algae, gorgonians and other encrusting organisms). It is called an extraoral feeder since in order to feed it forces its stomach through its mouth. This membranous structure (see Fig. 10) is positioned around the irregularities of the coral with the help of the starfish's tube feet. The stomach then is thought to secrete an enzyme which breaks down the coral tissue, unlocking the major energy reserves of the coral (which are in the form of waxes). This material is then transported by cilia (small hairs) to the caeca where they are absorbed. A specialised animal indeed! The feeding process may take from 4-6 hours. Once digestion is completed the stomach is retracted and the starfish moves off leaving behind a white coral skeleton.

Figure 10 This crown-of-thorns starfish was pried away from the coral on which it was feeding. Its membranous stomach can be readily seen.

Crown-of-thorns starfish have been estimated to consume about 5-6 m2 of coral tissue per year. Like many other starfish, it may survive without feeding for up to 9 months. During such times it is thought to live off energy reserves stored within its body.

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