Depth Influences Symbiodiniaceae Associations Among Corals on the Belize Barrier Reef.

In Belize, shallow populations (10 and 16 m) of the coral species from the back reef and reef crest are genetically differentiated from deeper populations on the fore reef and reef wall (25 and 35 m). Like many species of scleractinian corals, has an obligate symbiosis with dinoflagellate microalgae from the family Symbiodiniaceae. Here, we describe the Symbiodiniaceae taxa found within previously sampled and genotyped populations along a depth gradient on the Belize Barrier Reef by implementing high-throughput sequencing of the region of Symbiodiniaceae ribosomal DNA and the analysis framework. While Symbiodiniaceae type profiles across all sampling depths were almost entirely (99.99%) from the genus (formerly Clade C), shallow (10 and 16 m) populations had a greater diversity of type profiles in comparison to deeper (25 and 35 m) populations. Permutational multivariate analysis of variance (PERMANOVA) confirmed significant differences in type profiles between shallow and deep sample populations. Overall Symbiodiniaceae communities changed significantly with depth, following patterns similar to the coral host's population genetic structure. Though physiological differences among species in the cosmopolitan genus are not well-described, our results suggest that although some members of are depth-generalists, shallow populations in Belize may harbor shallow-specialized Symbiodiniaceae not found in deeper populations.