Juniper Publishers - Journal of Oceanography Abstract Bacteria on substrata certainly influence metamorphosis and settlement of coral larvae. We isolated bacteria from substrata and screened them for the capability of inducing or inhibiting metamorphosis of Acropora. Out of 468 isolates, only eight isolates revealed metamorphosis- inducing activities, which were weak or non-reproducible. Three of those isolates were identified as Alteromonasspp. Based on by 16SrDNA.On the other hand, metamorphosis-inhibiting bacteria were obtained efficiently, two out of 20 isolates, indicating a majority in bacterial communities on substrata. One revealed quick but temporal inhibition and the other revealed slow but persistent inhibition onto the metamorphosis induction by a peptide hormone. Thus, at least two inhibition pathways are suggested. Both of the two strains turned out to belong to the genus Pseudoalteromonas. Responses of coral larvae to mixtures of exclusive cues o