Settlement competency periods and dispersal potential of scleractinian reef coral larvae

The extent to which larvae from broadcast spawning scleractinian reef corals are retained on their natal reef and contribute to localized recruitment, or are dispersed between reefs, and their potential for long-distance dispersal, are largely unknown. Larval development and settlement competency periods were studied using planulae reared from the broadcast spawning reef coral Acropora longicyathus and Acropora hyacinthus from One Tree Island reef in the southern Great Barrier Reef Region, Australia. More than 35-47% of planula larvae began attaching to settlement tiles between 2-3 days after spawning, with larval metamorphosis and permanent settlement initiated within a few days afterwards. This rapid development and early attachment behavior increases the probability of some coral larvae being retained close to their natal reef system, and may result in a degree of self-seeding in some coral populations. Peak periods of larval metamorphosis and permanent settlement of A. longicyathus larvae occurred within the first few weeks after spawning, hence some coral larvae are likely to be dispersed away from their natal reef, promoting genetic exchange among populations on separate reefs. Maximum settlement competency periods of 1-3 months have been recorded for some planulae of broadcast spawning corals, indicating that these larvae have the potential for longer-distance dispersal and settlement on geographically distant reefs. Therefore, long-distance larval dispersal is likely to contribute to the broad biogeographic ranges of some coral species.