Post-settlement survivorship of artificially supplied Acropora coral larvae in the Sekisei Lagoon

ABSTRACT: Coral survivorship immediately after settlement remains relatively unknown despite many published reports on the larval recruitment of reef corals. This may be due to difficulties in the field observation of wild coral settlers. In this study, we compared Acropora coral survivorship immediately after settlement using a lattice-shaped plate that prevented fish grazing and sedimentation. To clarify the contribution of post-settlement survivorship toward the establishment of coral populations in different habitats, post-settlement survivorship was compared among 5 sites. Each site had different coral coverage: low in 3 sites and high in 2 sites. Six months after settlement, there was no significant difference in post-settlement survivorship between sites, except at one site where the settlement density was extraordinarily high. Extremely low survivorship was observed at that site probably because of a crowding effect. In terms of the substrate condition, macroalgae were abundant at sites where the coral cover was low. However, shading by macroalgae had a negative effect only on the growth of coral spats and not on their survivorship. The coral survivorship dropped sharply at one site 15 mo after settlement and 26 mo after settlement at another site. These results suggested that key factors associated with the high mortality of coral juveniles may vary temporally and spatially, even within a lagoon.