Aggregative predation by A. planci is very often observed on reef flats. Our research indicates that damaged corals may release AA and attract more A. planci. On the other hand, it is known that phospholipase A2 (PLA2) contained in the body of A. planci (Shiomi et al., 1985) produces AA from glycerophopholipid. Therefore, AA released by PLA activity in A. planci may, in turn, attract further A. planci and so on (Fig. 6). The 2 pheromonal function of these unsaturated fatty acids in seawater is quite interesting. Identification of the receptors on the sea star for AA and LA will require further study. In the present paper, we found the feeding attractants for the sea star A. planci and confirmed the efficiency of the attractants in the aquarium experiments. Although further studies were extensively needed for practical use of our attractants in the coral reefs, we were able to indicate a possibility of new methods to protect corals against A. planci.