Specificity in communities of Symbiodinium in corals from Johnston Atoll

The diversity of endosymbiotic dinoflagellates (Symbiodinium) in corals at Johnston Atoll in the central Pacific Ocean was assessed using both the internal transcribed spacer 2 (ITS2) region of the nuclear rDNA and chloroplast 23S rDNA. More sequences were recovered from corals using the ITS2 primers than with the chloroplast 23S primers, a finding that reflects both the higher taxonomic resolution and level of intragenomic variation in ITS2 in eukaryotes as compared to chloroplast 23S. Parsimony network analysis, Bray-Curtis coefficient of similarity and 1-way analysis of similarity resolved coral species- and/or genus-specific lineages and/or groupings of Symbiodinium that were generally congruent between the 2 genetic markers. Comparison of coral-Symbiodinium assemblages at Johnston Atoll with those in corals sampled on other reefs in the Pacific reveals differences that include novel host-symbiont unions and a Symbiodinium lineage previously reported to be Caribbean-specific in Acropora from Johnston Atoll.