Investigating the driving mechanisms behind differences in bleaching and disease susceptibility between two scleractinian corals, Pseudodiploria strigosa and Diploria labyrinthiformis

Disease and bleaching are two conditions which commonly lead to coral death. Among coral species, susceptibility to disease and bleaching is variable, and Pseudodiploria strigosa tends to be diseased more than Diploria labyrinthiformis, while D. labyrinthiformis bleaches more readily. The focus of this dissertation was to investigate and compare multiple components of these two coral species, and identify how they may relate to disease and bleaching resistance. Compenetnts examined included the surface mucopolysacharide layer (SML) thickness, gene expression, microbial associates, and a white plague aquarium study. The SML thickness decresased with increasing temperature regardless of coral species, indicating that SML thickness does not likely play a role in differences between susceptablities of these two coral species. However, Diploria labyrinthiformis had a lower mortality rate at 31°C, had fewer differentially expressed genes assossiated with stress, and upregulated genes associated with innate immunity in the summer, all of which may contribute to its relative disease resistance. The bacterial associates of each coral species were also monitored. Differences between the two coral species were primarily caused by Clostridia, Gammaproteobacteria, and rare species which may contribute to the relatively higher disease susceptibility of P. strigosa. Lastly, an aquarium study suggested that a potential pathogen of the Roseobacter clade infects both D. labyrinthiformis and P. strigosa, and might be transmitted by the Cryptochiridae gall crab, indicating that potential disease vectors associated with these two coral species may also play a role in disease resistance and resilience