Corals are declining rapidly almost everywhere in the world – archyworldys

Its area is modest, but its power of attraction enormous: coral hardly occupies more than 0.2% of the ocean floor, but its reefs contribute to their immense biodiversity and are home to at least 25% of marine species. However, his state of health is extremely worrying. Between 2009 and 2018 globally, 14% of corals died, or nearly 11,700 square kilometers, more than all of those living on Australia’s coral reefs. The decline can be seen almost everywhere on the planet.

This is the sad observation of the most detailed analysis to date devoted to this very special species. Published Tuesday, October 5, it stems from the work of 300 researchers who participate in the international monitoring network of the International Coral Reef Initiative (ICRI), and is based on more than 2 million data collected over forty years (from 1978 to 2019) in more than 12,000 sites in 73 countries.

This extensive analysis shows that heat waves are currently the main danger, as they generate more and more frequent bleaching phenomena. Reefs no longer have the time necessary for their regeneration between two stress episodes. These conclusions resonate with those of the IPCC (Intergovernmental Panel on Climate Change), which estimated, in its 2019 Special Report on the Ocean and the Cryosphere, that 70% to 90% of coral could disappear with a 1.5 ° C temperature increase. With an additional 2 ° C, almost all of it, 99%, would be doomed.

A before and after 1998

Serge Planes, research director at CNRS, does not share this grim prognosis. “It would be fairer to say that 80% or 90% of corals – there are 1,200 species – will transform. They will continue to fulfill certain ecosystem functions, but it will no longer be the same diversity of shapes and colors ”, assures this Criobe expert, who is one of the co-authors of the ICRI report.

According to this document, there is a before and an after 1998. In that year, marked by one of the most intense El Niño climatic phenomena ever recorded, a heat wave resulted in massive bleaching, particularly in the Indian Ocean, Japan and the Caribbean region. About 8% of the corals died within a few months.

As these bleaches occur – a sign of a breakdown in the symbiosis between the animal and zooxanthella, the photosynthetic unicellular algae that lodges in its tissues and provides it with energy – algae gradually take over. . “The balance of the ecosystem is upset when algae mats 5 to 10 cm high are formed on the coral substrate, depriving the organism of light”, specifies Serge Planes.

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