Symbiodinium hosts and seawater Targeted loci environmental. Symbiodinium hosts and seawater

Large scale environmental disturbances and stochastic events may impact both partners in coral host-Symbiodinium systems. Elucidation of the patterns of assembly in such complex and interdependent communities may enable better prediction of environmental impacts across the reef system as a whole. In this study, we investigated how the patterns in community composition and diversity of dinoflagellate symbionts in the genus Symbiodinium are distributed among 12 host species from six taxonomic orders (Actinaria, Alcyonacea, Miliolida, Porifera, Rhizostoma, Scleractinia) and in the environment at a local scale in the Great Barrier Reef. 454 pyrosequencing of the ITS2 region of Symbiodinium yielded 83 Operational Taxonomic Units (OTUs) at a 97 % similarity cut off. Approximately half of the Symbiodinium OTUs from the environment (reef water or sediments) were also present in symbio. OTUs belonged to six clades (A-D, G, and F), but community structure was uneven. The two most abundant OTUs (100 % matches to types C1 and A3, respectively) comprised 91 % of reads and OTU C1 was shared by all species. However, sequence-based patterns within these dominant OTUs revealed host species-specificity in some cases, suggesting that genetic similarity cut-offs for the analysis of Symbiodinium ITS2 data sets need careful evaluation. Of the less abundant OTUs, roughly half occurred at only one site or in one species and the background Symbiodinium communities in individual samples were distinct from each other. We conclude that sampling multiple host taxa with differing life history traits will be critical to fully understand the symbiont diversity of a given system, and to predict ecosystem responses of corals to environmental change and disturbance considering the differential stress response of the taxa within.