The planet lost 14% of its corals between 2009 and 2018, according to a vast analysis conducted by a network of 300 researchers. A decline that threatens marine life. In issue, mainly, climate change.
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Its area is modest, but its enormous attraction power: coral does not occupy only 0.2% of the ocean funds, but its reefs contribute to their immense biodiversity and are home to at least 25% of marine species. But his state of health is extremely worrying. Between 2009 and 2018 worldwide, 14% of corals died, nearly 11,700 square kilometers, more than all those living on Australian coral reefs. The decline is observed almost anywhere on the planet.
This is the sad finding of the most detailed analysis to date devoted to this particular species. Published Tuesday, October 5, it comes from the work of 300 researchers who participate in the global international monitoring network for Coral Reefs (International Coral Reef Initiative, ICRI), and relies on more than 2 million data collected in forty years (from 1978 to 2019) in more than 12,000 sites of 73 countries.
This extensive analysis shows that heat waves are currently the main danger because they generate more and more frequent bleaching phenomena. The reefs no longer have the necessary time for their regeneration between two episodes of stress. These conclusions resonate with those of the IPCC (group of intergovernmental experts on the evolution of climate), which felt, in its special report on the ocean and the 2019 Cryosphere, that 70% to 90% of the coral could disappear with a temperature increase of 1.5 ° C. With more than 2 ° C, it is even almost all 99%, which would be condemned.
A before and after 1998
Planes Serge, research director at the CNRS, does not share this dark prognosis. “It would be more fair to say that 80% or 90% of corals – there are 1,200 species – will turn itself. They will continue to fulfill certain ecosystem functions, but it will no longer be the same diversity of forms, of color”, Ensures this expert from Criobe, which is one of the co-authors of the report of ICRI.
According to this document, there is a forward and one after 1998. That year, marked by an El Niño climate phenomenon among the most intense ever recorded, a heat wave has resulted in massive bleaching, particularly in the Indian Ocean, Japan and the Caribbean region. About 8% of the corals died in a few months.
As these laundry occurs – a sign of a breaking of the symbiosis between the animal and zoxanthelle, the photosynthetic unicellular seaweed which lodges in its fabrics and brings it energy -, algae take Gradually the top. “The equilibrium of the ecosystem is broken when it is formed of the algae mats of 5 to 10 cm high on the coral substrate, depriving the light body”, precise Serge planes.
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