Crown-of-thorns starfish substrates with their arms and, when offered a choice of substrates, tend to settle on coralline algae, which they will subsequently feed on. In the classic pattern for echinoderms, the bilaterally symmetrical larva is replaced by a pentamerously symmetrical stage at metamorphosis, with the latter's body axis bearing no relationship to that of the larva. Thus the newly metamorphosed starfish are five-armed and are 0.4–1 mm diameter. (Note the size of the tube feet relative to the size of the animal.) They feed on the thin coating layers of hard encrusting algae (coralline algae) on the undersides of dead coral
Crown-of-thorns starfish of the fauna of most coral reefs and the effects of "A. planci" populations on coral reefs are very dependent on the population density. At low densities (1 to perhaps 30/hectare) the rate at which coral is being preyed upon by the starfish, is less than the growth rate of the coral, i.e. the surface area of living coral is increasing. The starfish may, however, influence the coral community structure. Because the starfish don't feed indiscriminately they may cause a distribution of coral species and colony sizes that differs from a pattern without them. This is evident by comparison of