Coral resistance

Because we protect better what we know well, researchers are delving into the genome of corals to identify what gives some of them a resistance to temperature that is so useful in these times of ever-rising water temperatures.

Over 25% of coral reefs have died in the last thirty years. The cause of this slaughter? " Rising water temperatures", answers Jérémie Vidal-Dupiol, researcher at the Host-Pathogen-Environment Interactions*. This is because corals live in symbiosis with zooxanthellae, unicellular algae that provide corals with oxygen and nutrients in exchange for shelter and food. "But when the temperature rises, the symbiosis ceases and the coral loses its zooxanthellae, leading to bleaching. This phenomenon considerably weakens the coral and increases its mortality rate.

According to a study published by Unesco in 2017, if ocean warming continues at its current rate, coral reefs could disappear by 2050 as a result of this thermal stress. So what can be done to preserve this unique biodiversity? " We're adopting protective measures, and even restoring coral reefs by taking cuttings and transplanting them elsewhere, but for the time being we're not optimizing our efforts," explains Jérémie Vidal-Dupiol. To make these measures more effective, the researcher is banking on epigenetics. The idea is to use sequencing data to identify the epigenetic biomarkers of the individuals best trained to withstand thermal stress, and therefore the most resistant to temperature rises. " Because these thermo-tolerant corals are the ones that will best cope with global warming", explains the specialist.

Temperature tolerance score

To kick off this ambitious project, aptly named SAVE, we headed for New Caledonia, the Fiji Islands and Tahiti, where we immersed ourselves with researchers who collected corals and their zooxanthellae, then subjected them in the laboratory to "ecologically realistic" thermal stress. After a month and a half of monitoring, each individual is assigned a temperature tolerance score. "We will then identify genetic, epigenetic and transcriptomic biomarkers for these corals and their symbionts." This data is invaluable for restoration projects, as it will enable us to focus on those individuals with the best adaptive capacities, and therefore the best chances of survival. " This information is also essential for conservation biology and ecosystem management, as it will enable us to better identify areas to be protected", adds Jérémie Vidal-Dupiol.

To support managers in this mission, the researchers are working in collaboration with the Sys2Diag laboratory on a revolutionary idea: "to use these results to develop a rapid thermo-tolerance test that will enable them to easily determine which individuals are most resistant to global warming". For coral reefs, resistance is getting organized.

*IHPE (CNRS, Ifremer, UPVD, UM)