The links between thermal coral reef bleaching and Vibrio pathogens as causative factors of yellow band disease

This dissertation identifies and confirms the coral pathogens associated with Yellow band disease (YBD) and the complexity behind the genetic identification of the bacteria associated with this coral disease, the role of thermal stress on the rate of spread and its virulence. The thesis research unravels the mechanisms by which yellow band Vibrio bacteria attack the symbiotic algae living in the tissues of reef building corals, thereby classifying this pathology a disease of the zooxanthellae. 16S rDNA oligonucleotide gene sequences were investigated and demonstrated to show distinct similarities between the bacterial strains from four new Vibrio spp. These new species show a close homology to Vibrio alginolyticus and vulnificus, which are known shellfish pathogens that produce toxins at higher temperatures. Cytological analysis and transmission electron microscopy of infected tissues show degenerative zooxanthellae, cell vacuolation, and cell lyses are apparent in all diseased specimens. Impairment of the cell cycle is evident along with a significant decrease in chlorophyll pigments, zooxanthellae cell density and cell mitosis. This thesis highlights the severity of YBD and the potential links between global warming induced coral bleaching and the cellular mechanisms that are effected when higher temperatures and Vibrio pathogens infect the major reef building corals of the Caribbean.