Post-settlement growth and mortality rates of juvenile scleractinian corals in Moorea, French Polynesia versus Trunk Reef, Australia

Abstract

Patterns and processes affecting juvenile scleractinian corals have received very little attention due to difficulties associated with detecting small corals on natural substrata. However, processes occurring during juvenile life stages are likely to play a strong role in population ecology. In particular, spatial differences in juvenile demographic rates may result in prominent differences in population and community structure for corals. In the present study, we compared the density, taxonomic composition, size structure, growth and mortality rates of juvenile corals (≤50 mm) and the cover and composition of adult coral assemblages among sites on Trunk Reef (central Great Barrier Reef) and Moorea (French Polynesia). There was significant regional variation in the taxonomic composition of coral assemblages within both adult and juvenile assemblages, with Pocillopora being the predominant coral genus in Moorea and Acropora at Trunk Reef. However, there were no differences in the density, growth or mortality rates of juvenile corals between Moorea and Trunk Reef. Most of the variation in these variables was evident at the small (within-reef) scale, with exposed sites having lower densities and higher rates of mortality of juvenile corals than sheltered sites at both locations. The lack of geographic variation in the density, growth and mortality rates of juvenile corals is interesting given that the cover of adult coral was 3-fold higher on Moorea (31.1%) than Trunk Reef (10.8%), suggesting that adult coral assemblages are structured more by differential adult mortality, larval settlement or very early post-settlement mortality (before colonies can be observed in situ), rather than demographic rates of juvenile growth or mortality.