The role of the microbiome in coral bleaching - Friends or Foes?

Project Rationale
Shallow-water coral reef ecosystems are on decline globally, with heat stress and deteriorating water quality identified as major causes of coral bleaching and subsequent mass mortality (1,2). The main habitat-founding species, scleractinian corals, are described as a holobiont formed by the coral host animal, its endosymbiotic dinoflagellates and the ‘coral microbiome’ – constituted by highly diverse and abundant communities of microbes living on and within the coral. While intense research efforts have focused on how the animal hosts and dinoflagellate symbionts respond to environmental stress, recent evidence suggests that the coral microbiome changes along environmental gradients and that this process may influence coral resilience to stress (3). Although marine microbes are known to be key drivers of global biogeochemical cycles; their exact functional roles in the coral holobiont remain unknown. It is unclear how specific environmental parameters shape the structure of coral microbiome, and which specific mechanisms and microbes drive the healthy functioning of the holobiont. This project aims to study how environmental multistressors, especially heat and nutrient stress, influence the composition of the microbiome and their interactions with their hosts in different coral species; thus affecting the resilience of corals and their capacity to recover from bleaching events.

Methodology
The study will use coral experimentation under tightly controlled laboratory conditions in combination with biogeochemical measurements and contemporary molecular biological techniques and bioinformatic analyses. Replicate colonies of established strains of model coral species representative for coral reef ecosystems around the globe will be cultured in separate compartments of the University of Southampton’s experimental coral reef mesocosm facility at the National Oceanography Centre Southampton (NOCS). Corals in dedicated aquaria systems will be subjected to different experimental conditions that cover a range and combination of environmental stressors (e.g. nutrient and heat stress), as well as short- and long- term exposure. Corals will then be allowed to recover under ambient conditions. Microbial assemblages within corals will be characterised before, during and after treatments, for their community structure as well as functional gene expressions. Both targeted and meta- omics analyses will be used to identify the key microbial taxa and their metabolic functions in response to environmental stress. Various physiological responses of the coral holobiont, including host and dinoflagellate symbiont, will be monitored throughout the experiments via microscopic analyses and tissue preparations. Changes in seawater chemistry such as inorganic/organic nutrient levels will also be continuously assessed.

Training
The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multidisciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at School of Ocean and Earth Science. Specific training will include: coral husbandry and experimentation, biogeochemical measurements, various state-of-the-art molecular biological techniques and bioinformatic analyses as required. Opportunities to attend and present results at relevant national/ international conferences and workshops are available throughout the course of study and are strongly encouraged.