Coral recruitment at a high latitude Pacific site: a comparison with Atlantic reefs

Reports of coral recruitment in subtropical Australia have indicated low recruitment rates of broadcast-spawning species, and higher but variable rates for brooded larvae. Hypotheses have suggested that coral biogeographical patterns and population dynamics on these subtropical reefs are a function of sporadic episodes of high recruitment by tropical coral larvae, on a time scale in the order of decades. In a study of coral recruitment in the Solitary Islands Marine Park in eastern Australia spanning an eight year period, recruitment was consistently low at two islands, and low to moderate at another three. Recruitment at each site varied interannually by a factor of four to seven times. For acroporid corals, the dominant broadcast-spawned recruit in tropical eastern Australia, only 34 recruits were recorded from 370 pairs of settlement panels collected over the 8 yrs, indicating either that the temporal scale of recruitment events for this species is greater than the time scale of the study, or that the local population is maintained by a lower level of recruitment than previously assumed. While the coral recruitment rates at the Solitary Islands were low relative to tropical Australian sites, they were comparable with rates reported from both tropical and subtropical sites in the western Atlantic Ocean. This suggests that the relatively low levels of larval settlement reported for these sites are sufficient to maintain coral communities, and that the sporadic episodes of recruitment of tropical larvae hypothesized for high latitude sites, while potentially significant biogeographically, are not necessary for population maintenance.