Abstract. Coral-associated bacteria have been proposed to provide important functions in promoting corals’ success by enhancing nutrition, enabling nutrient cycling and providing resistance against diseases. While coral microbiome research is increasing, we still have a limited understanding of the bacterial community structure and role in coral species and reefs. This research compares the bacterial assemblages in various coral species, environments and stress conditions to describe their variability and persistence, and to provide a roadmap to guide focused studies investigating bacterial function in corals. In healthy corals, bacteria’s diversity reaches 10’s of thousands of distinct phylotypes. Each coral species is found to have distinct bacterial composition, and these respond in synchronicity to changes across spatial scales and depths. Alpha- and Gammaproteobacteria are the most common bacterial classes and some bacteria are consistently found across coral species and reef habitats, for example, one phylotype of the family Alteromonadaceae was found in 98.4% of all coral samples. Bacterial assemblages in severely bleached corals are different to those described in healthy corals. In bleached corals, Alpha- and Gammaproteobacteria are diminished, and conversely rare bacterial species increase, thus disrupting the normal symbiotic taxonomical structure observed in healthy corals. I propose to dissect the coral microbiome in three distinct microbial sub-groups: a ubiquitous core microbiome of very few symbiotic bacteria; an environmentally responsive microbiome of phylotypes reef- and taxa-specific; and a highly variable transient community. This research contributes to the understanding of the coral microbiome structure and function, and presents key knowledge to decipher the response of coral holobiont to future anthropogenic stressors and the identification of bacterial key species.

Biography. Alejandra is an awardee of the Australia Awards Scholarship, pursuing a PhD in the ARC Centre of Excellence for Coral Reefs Studies, James Cook University. She is interested in coral microbial ecology, and microbial contributions to coral success and functioning. To investigate these topics, Alejandra is exploring bacterial communities in diverse coral species along different environments in the Great Barrier Reef and the Coral Sea. As part of her research she is exploring approaches employed at other complex bacterial-host systems where microbial contributions have been well-established to propose and test hypotheses about the bacterial role in corals, while disentangling its complexity.