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Abstract
Coral reefs are vibrant biodiversity hotspots that provide socio-economic services to communities worldwide. Scleractinian, or stony, corals are essential foundation species that build the three-dimensional structures of coral reef habitats. The surface mucus layer of stony corals contains an immense diversity of microorganisms including Vibrio, one of the most diverse marine bacterial genera. Vibrio are ubiquitous in coastal environments and are well-known human pathogens. Opportunistic Vibrio are also commonly implicated in coral diseases. Globally, contemporary coral reefs continuously face pronounced changes in biotic and abiotic conditions. Biotic stressors, such as disease, threaten coral health. Abiotic stressors, such as episodic nutrient input, may alter coral resilience. The effect of changing environmental factors on coral microbiomes has only been studied in the last 15 years, and further research is needed to ascertain reef-associated microbiome responses and Vibrio dynamics when biotic and abiotic conditions are unfavorable. Therefore, this dissertation investigates how the bacterial microbiomes of coral and reef water in the Florida Keys, USA responds to biotic and/or abiotic stressors. First, by confining spatiotemporal variability, data from a multi-species, multi-disease outbreak provides a unique opportunity to test trending frameworks used to describe coral disease dynamics. Results reveal commonalities and differences between coral microbiomes affected by the outbreak, suggesting that two seemingly competing frameworks are not mutually exclusive. Next, this dissertation describes the effect of trans-Atlantic Saharan dust deposition on coral-associated microbiomes and Vibrio bacteria in Acropora palmata and Orbicella faveolata. During a 26 d time series, dust deposition alters the composition and structure of bacterial communities and rapidly increases the abundance of Vibrio. These changes are ephemeral, and communities subsequently returned to baseline conditions. Lastly, reef water metatranscriptomes were analyzed from concurrently collected seawater samples. Results show differential gene expression in response to fluctuating dust aerosol optical thickness, dissolved iron concentration, and dissolved organic carbon concentration associated with trans-Atlantic Saharan dust deposition. In summary, the research presented here contributes to a foundational understanding of the interactions between the coral host, its associated microorganisms, and the environment.