World Oceans Day: France must save its coral reefs!

It is a small financial step, but a big boost for French research in the maritime field. Two years after a solemn speech in Montpellier – “Protecting the ocean is an imperative at least as great as the protection of the Amazon” -, Emmanuel Macron unblocks today, on World Ocean Day, 40 million for the “Ocean and Climate” research program (PPR). One way for CNRS and Ifremer to launch a series of calls for projects in order to reorient the scientific community around seven challenges: predicting the impacts of extreme phenomena linked to climate change in overseas territories, intensifying research in the oceans polar, ocean pollution (characterize the “exposome”), observe and model the ocean, improve the protection and resilience of marine environments, exploit resources based on the science of sustainability, share with the general public the discovery of the ocean and the associated societal issues.

Why coral reefs are precious

The first of these challenges, the fight against extreme events, therefore more particularly concerns our overseas territories. With, in the first line, their physical protection. However, one of the natural barriers that surround our three main areas – the Caribbean (Guadeloupe, Martinique), the Pacific (Polynesia, New Caledonia) and the Indian Ocean (Reunion, Mayotte) – is the coral reefs. “They protect the coastline from erosion and submersion, in particular from the effects of swells,” recalls Jean-Pierre Gattuso, CNRS research director at the Oceanographic Laboratory of Villefranche-sur-Mer and member of the PPR scientific committee. These solid barriers absorb 97% of wave energy, reducing damage to coastal developments during extreme events such as cyclones or tsunamis. Locally, corals also have a significant economic weight: the French Initiative for Coral Reefs (Ifrecor), which on June 8 is publishing a study covering five years of monitoring, estimates that they represent the equivalent of 1.3 billion euros contributed to the economies of 9 overseas communities, ie 12,000 companies, 50,000 jobs and more than 175,000 households concerned. An economic weight which weighs more particularly in the sector of “blue” tourism (hotels, restaurants, diving centers) in particular in the Caribbean, but also in the field of fishing: “All Polynesians are fishermen and 80% of their proteins are from the sea “, explains Catherine Gabrié, Environmental Consultant and main author of the Ifrecor study.

On a larger scale, globally, coral reef fishing supports some 6 million people and is worth $ 6.8 billion annually. Finally, with regard to biodiversity, the role of these ecosystems, which represent only 1% of the surface of the oceans, is crucial since they help support a quarter of marine species. “It’s a bit like the tropical forest of the sea in terms of plants and animals”, abounds Jean-Pierre Gattuso.

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More and more bleaching episodes

But today, the state of coral reefs is worrying. For twenty years, several episodes of “bleaching” have been observed. Those on the Great Barrier in northeastern Australia have been widely publicized but the phenomenon is widespread since currently a third of corals are threatened. “They are marine animals, just like sea anemones. Inside their cells, they have microalgae that feed them, explains the specialist from the Oceanographic Laboratory of Villefranche-sur-Mer. temperature of the water, the corals undergo a stress which causes them to expel these microalgae, which are essential to their survival, and turn white. ” If this warming of barely 1 ° C. lasts over time (several months) the bleaching phenomenon can lead to the death of the coral and the entire ecosystem. This is what was observed in several places on the Great Barrier, particularly in 2016. On the other hand, the phenomenon is reversible if the warming episodes are of less intensity (less than three to four weeks). Again, this is what has been observed over the past five years. “In the French overseas territories, there is an acceleration in bleaching episodes. We saw it in 2016, 2018, 2019 and 2020”, notes Catherine Gabrié. These increasingly frequent events are getting closer in time, but there has been no significant mortality. For the Ifrecor specialist, this resilience of coral reefs is fundamental. Whether in New Caledonia in March 2003 (after Cyclone Erica) and Polynesia in 2010 (destruction linked to the starfish, an invasive species), each time, the ecosystem has recovered in barely a decade. .

To save them, we must act now

The Oceanographic Laboratory of Villefranche-sur-Mer worked with numerical models on the future evolution of reefs according to two scenarios with high and low CO2 emissions. In the first case, if the temperature of the oceans is not controlled and continues to rise by 3 to 5 ° C by 2100, the corals will inexorably disappear. In the second case, if we stay within the limits set by the Paris Agreement (limit warming to around 2 ° C), some corals will continue to adapt and should survive bleaching. “We therefore have a limited period of time to act, that is to say by 2050, and we must do so now,” said Jean-Pierre Gattuso.

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The first lever is obviously the reduction of carbon emissions on a global scale. “But our studies show the preponderant part of the reduction of the pressures resulting from human activities on land and at sea, underlines Catherine Gabrié. It is above all a question of political will.” In the Overseas Territories, the emphasis must be placed on sanitation (put an end to the catastrophic management of wastewater), the limitation of erosion (development), better supervise agricultural practices but also activities. tourism and finally, encourage more sustainable fishing. “The last flagship measure will involve the protection of coral reefs, that is to say by setting up a maximum of marine protected areas”, continues Jean-Pierre Gattuso. Today, 67% of reefs are classified in this category and the stated objective would be to reach 100% by 2025. Provided that a high level of protection is put in place in the most populated areas. “Fighting against coral bleaching will be a difficult battle in the coming years but their resilience and adaptation capacities are remarkable, concludes Catherine Gabrié. We still have the cards in hand to prevent coral reefs from being the first ecosystems. major to collapse under the weight of global warming. ”


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