“Super corals”: why those of the Red Sea are incredibly resistant to rising temperatures

The corals of the Red Sea, in the Gulf of Aqaba, are particularly resistant to high temperatures. Researchers wanted to better understand this phenomenon. The result of their investigations was published on May 3, 2021 in the journal PNAS.

Exposure to high temperatures

Due to rising temperatures in the oceans, symbiotic algae, which give corals their color and nutrients, are forced out of coral structures. This results in a phenomenon called bleaching: corals become discolored at the same time as they weaken. But the corals of the Gulf of Aqaba are particularly resistant. To better understand the molecular mechanism behind this robustness, a team from the Ecole Polytechnique Fédérale de Lausanne (Switzerland) subjected these organisms to different temperatures, in particular those which may unfortunately be felt in the coming decades. “While the monthly average maximum water temperature is around 27 degrees in this region, the corals have been exposed to heats of 29.5 ° C, 32 ° C and 34.5 ° C, respectively. Short term, for 3 hours, and long term, for a week“, underlines the school in a press release. In parallel, the researchers measured the expression of the genes of the coral but also of the symbiotic algae.

Sheltered for 100 or even 200 years

The results obtained show that corals and their algae can withstand average temperatures 5 ° C higher than normal. “The main discovery is that we realized that these corals still live well below the tolerance threshold that their molecular mechanism can withstand, which protects them from temperature rises for 100 or even 200 years, summarizes in the press release Romain Savary, main author of this new study. Up to 32 ° C in any case, we were able to measure that they recovered without molecular sequelae and acclimatized to a short as to a long period of heat, as well as their symbiotic partners.“. Indeed, the temperature rise in the Red Sea is not expected to go beyond 5 ° C by the end of the century.

The key to the resistance of these corals lies in the level of gene expression. “It is a real concert of genetic expression that gives this super power to corals.“, notes Anders Meibom, director of the Laboratory of Biological Geochemistry at EPFL. This gene expression is now a reference for the scientific community which will now have a means of identifying these” super corals “as the researchers call them. However, these organisms, however resilient they are, do not represent a miracle solution for the safeguard of all the coral reefs on the planet, in particular the Great Barrier Reef which undergoes episodes of repetitive bleaching. “The coral is extremely dependent on its environment and in general only a long natural colonization would allow it to adapt elsewhere. In addition, the Great Barrier Reef is the size of Italy, it is impossible to reseed it artificially.“, recalls Anders Meibom. Only a spontaneous recolonization of areas weakened by the rise in temperatures is possible. But protecting the corals of the Red Sea, in order to maintain a healthy stock of robust organisms, remains particularly important so as not to notice one day. the total disappearance of these fascinating organisms.

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