Endosymbiotic Algal Community Dynamics within Corals at St. Lucie Reef, FL

The coral reef habitat at St. Lucie Reef Stuart, FL persists despite environmental instability resulting from extensive freshwater discharges, summer upwelling, and seasonality. By examining the symbiotic algae, or zooxanthellae, that reside in corals, we can gain insight to overall coral physiology during stress events. Two hermatypic corals, Montastraea cavernosa and Pseudodiploria clivosa were sampled over a year and a half, representative of wet and dry seasons. Zooxanthellae were isolated from each coral fragment and responses to water quality fluctuations were quantified by measuring cell density and chlorophyll a and c2. Both coral species varied in the amount of zooxanthellae harbored as well as chlorophyll concentrations. Pseudodiploria clivosa had a higher density of cells than Montastraea cavernosa, but chlorophyll concentrations per cell were greater in M. cavernosa. Morphological differences between both coral species and their zooxanthellae concomitant with the inverse relationship between cell density and chlorophyll could be indicative of photosynthetic capabilities. Genotypes of zooxanthellae within each host species were evaluated by amplifying the internal transcribed spacer region of ribosomal DNA and sequencing on Illumina’s MiSeq platform. Patterns in fine-scale diversity and genetic variation may explain the observed physiological differences among corals at St. Lucie Reef.