Calcified macroalgae and their bacterial community in relation to larval settlement and metamorphosis of reef-building coral Pocillopora damicornis.
Calcified macroalgae play an important role in the settlement and metamorphosis of invertebrate larvae in coral reef ecosystems. However, little is known about the algal-associated bacterial communities and their effects on larval settlement. In this study, the responses of larvae of the coral Pocillopora damicornis to calcified algae (Porolithon onkodes, Halimeda cylindracea, Halimeda opuntia, and Amphiroa fragilissima) were evaluated. The results revealed that P. onkodes and H. cylindracea significantly enhanced the rates of settlement and metamorphosis, whereas fewer larvae settled on A. fragilissima and H. opuntia. Amplicon pyrosequencing of the V3-V4 region of 16S rDNA was applied to investigate the relationship between algal bacterial community and larval settlement. Principal coordinates analysis demonstrated that the bacterial community composition of H. opuntia was more similar to that of A. fragilissima, but clearly distinct from those of H. cylindracea and P. onkodes. Furthermore, the relative abundances of bacteria were highly diverse among different algae. H. opuntia had higher percentages of Thalassobius, Pelagibius, and SM1A02; whereas the abundances of Mycoplasma and Suttonella were significantly higher in H. cylindracea than other algae. Our results showed that larval settlement/metamorphosis was strongly correlated with the bacterial community composition, and with the relative abundance of a few OTUs.