Coral acclimation to global warming: Uncovering the mechanisms of coral-symbiont dynamics and symbiont change (SYMCHANGE)

• Applicants: Professor Dr. Agostino Merico; Professor Dr. Christian Wild
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions ; Oceanography
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 553108951

Hard corals form the foundation of coral reefs. Their success is the result of an endosymbiotic association with photoautotrophic algae (symbiont hereafter). High water temperatures induce corals to expel their symbionts, a phenomenon called bleaching, which is the most prominent threat to coral reef ecosystems. Since some symbionts are more thermally tolerant than others, symbiont change (i.e., a shift of the symbiont community within corals) may constitute an acclimation mechanism of the coral-algae complex under global warming. Trade-offs between increased thermal tolerance at the expense of reductions in key physiological functions, such as coral growth and calcification, pose limitations to this hypothesis. In addition, the physiological mechanisms underpinning symbiont change and the related ability of corals to adapt to thermal stress are poorly understood. Here we propose to combine experimental ecology with mathematical modelling to identify the mechanisms and the environmental conditions that drive symbiont change and to assess the effects of this change on coral functions. Using the two widespread hard corals Stylophora pistillata and Montipora digitata, we will test if bleaching-inducing light and thermal stress conditions are essential for triggering symbiont change. By adding the thermally-tolerant symbiont Durusdinium trenchii in bleached coral cultures and by comparing these cultures to those without the addition of this symbiont, we may infer if recovery from bleaching involves an acquisition of new symbionts from the environment or an internal shuffling of symbionts already present within the coral-algae complex. During these experiments, we will further investigate changes in symbiont population and composition along with biogeochemical coral functions (e.g., growth, photosynthesis, calcification) using molecular and eco-physiological tools. Mathematical modelling will integrate the relevant information gained from the laboratory experiments into a broader and more flexible simulative context. Numerical experiments will allow us to explore different coral acclimation hypotheses related to symbiont change and their effects in the context of varying environmental conditions. The synergistic combination of laboratory experiments with mathematical modelling is a promising approach to uncover the processes driving the relationship between corals and different symbionts, the mechanisms at the base of the changing symbiont populations, along with the costs and benefits associated with such changes. Our project will shed new light on the capacity of corals to respond to environmental perturbations and will contribute to the development of innovative strategies to support the functioning of coral reefs under the influence of climate change.

• DFG Programme: Research Grants
• Co-Investigators: Subhendu Chakraborty, Ph.D.; Dr. Benjamin Mueller