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This asteroid is a corallivore, almost exclusively consuming live sclerectinian corals. An average sized adult (40 cm) can kill up to 478 square cm of live coral per day through its grazing activities. The crown-of-thorns starfish can be seen as an ongoing disturbance factor on the reef, removing swaths of clonal corals in its path, and opening up bare areas of coral rock for settlement and recruitment of other species of sessile invertebrates. Thus, A. planci can be seen to have a role in diversifying the habitat. However, if coral cover is drastically reduced, populations of coral reef specialists (animals that depend exclusively on coral cover for shelter and food) may decrease. Thus the impact of A. planci in their environment depends on how abundant they become.
Acanthaster planci harbors several genera of ectoparasitic copepod crustaceans on its dermal surface.