World Oceans Day: we tell you the story of the Great Barrier Reef, in agony due to global warming

Once upon a time there was a strange, beautiful and flamboyant species, capable of building its own skeleton and multiplying. An animal with billions of individuals that takes the form of towers, rings or mountains. So solid that it is believed to be mineral. So beautiful that you imagine it plant. One day perhaps, future generations will speak of corals as a mythical creature. As sea temperatures rise and so do atmospheric temperatures, many coral reefs are succumbing to this new stress. The most famous of them, which make up the Great Barrier Reef off Australia, are no exception. On the occasion of World Oceans Day, Thursday June 8, franceinfo dives into the fascinating history of this dying ecosystem. It lived for 20 million years, but rising temperatures shattered its life Like all coral reefs in the world, the Great Barrier Reef was born of an unlikely love affair. This romance begins 20 million years ago, in the desolate waters bordering northeastern Australia, desperately poor in nutrients. The coral – a strange animal cousin of anemones and jellyfish – could have waited peacefully for evolution to settle its account. But our hero has resources. “To be able to live where there is no food, it has developed an exceptional physiological process: symbiosis, living together between two organisms,” explains physiologist Denis Allemand, a coral specialist. Its soulmate is a single-celled algae, the zooxanthellae. Together, these two species – one animal, the other vegetable – form both a daring mixed couple and one of the oldest co-dependent duos on our planet. Without waiting, the zooxanthellae move inside the coral. In his body, under his exoskeleton. Intrusive? No, vital. “Algae carry out photosynthesis and therefore produce oxygen and sugars which will be used by the coral animal”, explains oceanographer Pascale Joannot. In addition to its colors, coral draws its energy from it. Enough to give birth to the largest animal construction on the planet: 2,500 reefs spread over 2,300 km in length – the distance between Montpellier and Oslo (Norway) – populated by 400 species of coral. Their fusional love can be observed from space. Corals affected by bleaching, in the Great Barrier Reef, off Queensland, Australia, March 7, 2022. (GLENN NICHOLLS / AFP) But in 1998, the couple faltered. The Great Barrier is experiencing a first episode of massive bleaching. Under the effect of the stress linked to the increase in water temperatures, the coral expels the zooxanthellae. This phenomenon constitutes “a divorce”, describe Pascale Joannot and Denis Allemand. The coral loses its color, revealing its white skeleton, and especially its reason for living. If the separation lasts too long, the animal dies. A new crisis occurs in 2002. Then in 2016 and 2017. And again in 2020 and 2022. According to Australian researchers, only 2% of corals in the Great Barrier Reef escaped a bleaching episode and more than half of its corals have died since 1995. Under the effect of global warming, “massive bleaching events are occurring everywhere on the Great Barrier Reef. They are becoming more important, but also longer and more frequent”, warns Denis Allemand. It renders immense services to nature and our lives also depend on it The Great Barrier Reef is not just an extraordinary animal structure, whose towers can rise up to 500 m from the sea floor. It is a rich ecosystem in the middle of nothingness. “We often compare corals to oases in the oceanic desert”, explains Denis Allemand. It is the Dubai of manta rays, the Las Vegas of Nemo. A largely submerged megalopolis, it is home to 1,500 species of fish, 4,000 species of molluscs and 240 species of birds. Thirty species of whales and dolphins frequent it. Six of the seven species of sea turtles recorded in the world live there. “The wealth created by engineered coral attracts a host of organisms to the reef: 30% of known marine species live in coral reefs.” Denis Allemand, coral specialist at franceinfo Or, “when the oasis disappears, only the desert remains. It’s difficult to survive in the desert”, continues the coral specialist, pointing to the cascading effects of this loss of biodiversity in the food chain. Coral reefs as a whole provide 9-12% of the fish caught worldwide. “People who live nearby get 90% of their protein intake from coral reefs,” adds Pascale Joannot. Reefs also nourish souls. They have “a cultural value for these residents: they are found in stories, legends, totems, etc. They have a cultural and religious role”, she insists. Along the Great Barrier Reef, local indigenous communities are working to preserve it. Their jobs as rangers or guides depend on these mythical reefs, a paradise for divers – on land, tourism supports more than 60,000 people. Fish around the Great Barrier Reef, Australia, February 12, 2019. (ANTOINE BOUREAU / PHOTONONSTOP / AFP) The Great Barrier Reef feeds them, uses them and “protects the land against the onslaught of the ocean. A wave that breaks on a dead reef is less well stopped than when it breaks on a healthy reef”, continues the biologist. Corals also wish us well. The Monaco Scientific Center is thus studying coral as a “magnificent biological model”: “We are working on its ability to regenerate. It also has absolutely phenomenal antioxidant properties (…) or anti-aging properties”, details Denis Allemand. Against certain cancers, against pain, Alzheimer’s disease or osteoarthritis… Each species potentially carries a molecule that will lead to a treatment. A perspective that makes you want to take care of it. She is dying and our efforts to save her are like a sword in the water. A reef can recover from a bleaching episode in a few years. But the repeated attacks of the disease will one day overcome its resilience, condemning the Great Barrier. Because the reefs that recover have fewer species and the latter are generally among the least resistant, explains Pascale Joannot. In an attempt to remedy this critical state, the newly elected Australian government has prescribed the seriously ill a cure of greenbacks: it has promised to inject 1.2 billion dollars into the protection of this ecosystem by 2030. the dispersion in the ocean of inputs from human activity (industrial or agricultural), waging war on plastic, working to restore dying reefs… “For the moment, we are experimenting”, notes Pascale Joannot, carrier of the participatory program SOS Corail. “There are attempts at transplantation: we take healthy corals from a place where they are doing well and we try to get them taken elsewhere. Nurseries too”, quotes the scientist, welcoming the many initiatives carried out around the world to protect the reefs. “But that won’t be enough.” An atoll that makes up the Great Barrier Reef, Australia, on September 21, 2021. (DEICHMANN-ANA / ONLY WORLD / AFP) To guarantee that a reef will not be affected by a bleaching phenomenon, there are only an antidote: We can make fine speeches and spend billions, but to save the corals, we must slow down the global warming caused by human activity. Pascale Joannot, oceanologist at franceinfo Because underwater like everywhere else, the change in temperature – and the rise in acidity that accompanies it – is too rapid to allow this ecosystem to adapt, however fascinating and resilient it may be. -he. The scientific models validated by the IPCC thus anticipate the disappearance of 99% of corals in the event of a global increase in temperature of 2°C by 2100. However, according to the comparison of Climate Analytics programs, this is precisely where we lead the proposals of the new Australian Prime Minister. Yet presented as determined to tackle the issue of the country’s greenhouse gas emissions head-on, this government would therefore also condemn this jewel in the long term, not without having swallowed up the equivalent of the GDP of Samoa – a State which also sees its coral reefs dying – in its safeguard. Coral reefs, and in particular the Great Barrier “would be the first ecosystem to disappear because of man”, notes Denis Allemand. To avoid this, the coral specialist is counting on a global coral conservancy project, “a second best” nevertheless ambitious, consisting in recovering as many coral species as possible, in order to ensure their survival in the laboratory. Scientists hope to be able to select those “that we could use when things were better”, species that would resist a warmer ocean. From a miracle of nature to life in an aquarium, the fate of the Great Barrier Reef is not sealed. Provided, of course, that the species that abused him rushes to his bedside.