Big Data Approaches To Coral-Microbe Symbiosis

Coral reefs face increasing challenges worldwide, threatened by overfishing and nutrient pollution, which drive growth of algal competitors of corals, and periods of extreme temperature, which drive mass coral bleaching. I will discuss two projects that examine how coral’s complex relationships with microorganisms affect the response of coral colonies and coral species to environmental challenge. Microbiological studies have documented key roles for coral’s microbial symbionts in energy harvest and defense against pathogens. However, the evolutionary history of corals and their microbes is little studied. As part of the Global Coral Microbiome Project, we are characterizing bacterial, archaeal, fungal, and Symbiodinium diversity across >1400 DNA samples from all major groups of corals, collected from 15 locations worldwide. This collection will allow us to ask how coral- microbe associations evolved over evolutionary time, and to determine whether microbial symbiosis helps predict the relative vulnerability of certain coral species to environmental stress. In the second project, we experimentally characterized how the long-term effects of human impacts such as overfishing and nutrient pollution influence coral-microbe symbiosis. We conducted a three-year field experiment in the Florida Keys applying nutrient pollution or simulated overfishing to reef plots, and traced the effects on reef communities, coral microbiomes, and coral health. The results show that extremes of temperature and algal competition destabilize coral microbiomes, increasing pathogen blooms, coral disease, and coral death. Surprisingly, these local stressors interacted strongly with thermal stress: the greatest microbiome disruption, and >80% of coral mortality happened in the hottest periods. Thus, overfishing and nutrient pollution may interact with increased climate-driven episodes of sub-bleaching thermal stress to increase coral mortality by disrupt reef communities down to microbial scales.