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Science & Technology

ORIGINAL FRENCH ARTICLE: Réchauffement climatique. Sale temps pour les coraux

by Marion Gauthier

Global warming. Hard times for coral.

Translated Wednesday 6 September 2017, by Meghan O’Shea

According to Unesco, the twenty-nine coral reefs classified as World Heritage Sites will disappear by 2100... An optimistic timeline, according to the World Heritage Centre.

More than a million tufts of coral are picked and carried off every year by tourists.

Photo Grégory Boissy/AFP Photo

"We can’t waste any time, let’s enjoy them!" exclaimed Alphonse de Lamartine. Time is running out. Enjoy it while it lasts: before the end of the century, it could be that no one will be able to be overawed by the world’s coral reefs. Last April, Unesco carried out the first global scientific assessment of the impacts of climate change on coral reefs. The conclusions are without question: if greenhouse gas emissions are not reduced, the 29 sites classified as UNESCO World Heritage could be removed from the map by 2100. "When we look at future scenarios, it is clear that action is needed," says Fanny Douvere, Coordinator of the Marine Programme for the World Heritage Center, for whom "the future is more or less optimistic". She continues: "Each generation sees the corals, admires their colors, but none fully sees their progressive degradation.”

20% of the reefs have already disappeared

No longer are corals as beautiful as they once were... nor are they as numerous. According to the Oceanographic Institute of Monaco, 20% of reefs have already disappeared. Moreover, the phenomenon of whitening, observed for the first time in 1983, is intensifying. "The last three years have been the hottest ever recorded", reports UNESCO. This has caused a coral bleaching event that has affected 72% of the reefs included on the list of World Heritage Sites. Initially, illness and overexposure to light were blamed. This was incorrect: the bleaching is in fact the sign of a critical weakening of the coral, a consequence of episodes of high heat occurring at too frequent of intervals, themselves a result of global warming.

Coral lives in symbiosis with micro-algae, or zooxanthellae, which allow the coral to complete the photosynthesis process. The algae provide the nutrient resources and allow the coral to grow and form reefs. Increasing ocean temperatures, even by minimal amounts (1 to 2 degrees Celsius), disrupts this symbiotic balance and provokes an almost physiological reaction: just as the human body expels the bacteria that affect it, the corals expel the zooxanthellae, which now no longer function properly due to the heat. In so doing, they lose the color that the microalgae give them and reveal their skeletons. "The pure white of the reefs, once they have expelled their zooxanthellae, is misleading because the corals are very vulnerable and often end up being covered with stringy algae, which means that they have died," explains Joachim Claudet, a researcher with the French National Center for Scientific Research (CNRS) at the Insular Research Centre and Environmental Observatory. "In fact, corals are in competition for space with macroalgae," he adds, “When they whiten, they become weaker and the roles, in a way, reverse. It’s a regime change.”

According to him, however, bleaching is not the only factor in the disappearance of the coral: "The pressure exerted on coral reefs comes from different, interacting sources." Tourists are among their main predators,"more than a million strands of coral are harvested and carried away each year ". The impact of overfishing is also notable. "If there are fewer fish, the resilience of the ecosystem, its ability to recover, decreases. Herbivorous fish, for example, have a role in regulating the coral ecosystem.”

Certainly, but how? Nearly 25% of marine fauna depend on coral reefs; included with them are the food security, economic well-being and social bonds of a large part of the world’s population. UNESCO estimates the social, cultural and economic value of coral reefs to be $1 trillion. Robert Calcagno, director of the Oceanographic Institute of Monaco, also counts 500 million people whose "life and survival" are threatened by the diminution of the coral reefs. "A reorientation of their economies would be difficult, especially as it concerns poor people, most of them vulnerable," he said. Some countries see their very existence threatened, both from the point of view of resources and the fragility of their territory. The reefs constitute true breakwaters, which protect the coasts from sea incursions. So much so that "climate related migration is being considered very seriously by the people of Kiribati, an archipelago of coral islands in the Pacific," according to Robert Calcagno. Finally, he emphasizes the almost universal "affinity" for coral, "a rich, beautiful and colorful species". What arouses curiosity, however, does not seem to "awaken consciences", as the endangered corals, whose principle transgression has been to have take up residence under the water, far from humanity’s gaze, grab little attention. Happily for those in communities already being threatened: while not protected, they are, at least, easy to spot because they are so colorful.


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