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Coral bleaching: the 4th global mass death has begun

Coral bleaching

credits Benjamin L. Jones su Unsplash

54% of the world’s reefs are affected by coral bleaching

For the fourth time in 30 years, coral reefs between the Pacific, Atlantic and Indian oceans are dying on a massive scale due to the high temperatures of the waters. And this time it could be the worst ever. Coral bleaching currently affects 54% of global reefs but the percentage is growing by 1% every week. The worst coral bleaching event recorded so far dates back to 2014-2017 and has stopped at 56%.

This was announced by the National Oceanic and Atmospheric Administration (NOAA) of the United States, a few weeks after the first announcement of a possible coral bleaching mass. “From February 2023 to April 2024, significant coral bleaching has been documented in both the northern and southern hemispheres of each major ocean basin,” said Derek Manzello, coordinator of the NOAA unit monitoring the health of coral reefs.

What is coral bleaching and why is it important?

When the water temperature reaches very high values – typically during prolonged waves of sea heat -, the corals react to thermal stress getting rid of the microorganisms that populate them. These zooxanthellae algae, which give the reefs their color (hence the term “bleaching”), are essential to provide nourishment to coral polyps. The higher the temperature, the more likely the reef will not recover from the event.

Coral bleaching events on a global scale have consequences far beyond the most affected regions and not only on reefs. Coral reefs account for about 25% of marine species, including at least 4,000 species of fish. The collapse of reefs can therefore have cascading effects on other ecosystems and lead to the reduction of populations of many marine species.

Where is the mass death of corals happening?

Since the beginning of 2023, explains NOAA, mass bleaching of coral reefs has now been confirmed in all tropical regions. From Florida to the Caribbean, from Brazil to the eastern tropical Pacific, and from the Australian Great Barrier Reef to the Pacific archipelagos like Fiji and Vanuatu. But also in the Red Sea, in the Persian Gulf, on the eastern coast of Africa, and the western coast of Indonesia.

The main factor behind these 4 massive event – the previous ones date back to 1998 (20% of the world coral affected), 2010 (35%) and 2014-2017 (56%) – is the temperature of the global oceans, now more than 400 days at levels never reached before.

As the world’s oceans continue to warm, coral bleaching is becoming more frequent and severe,Manzello continues. “When these events are sufficiently severe or prolonged, they can cause coral mortality, damaging people who depend on coral reefs for their livelihood“.

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