Scientists have confirmed that the world’s worst ongoing global coral bleaching event has now affected nearly 84 per cent of the world's coral reefs.
The US National Oceanic and Atmospheric Administration in partnership with the International Coral Reef Initiative on April 15, confirmed that the world is witnessing its fourth global bleaching event.
The bleaching-level heat stress has impacted 83.7 per cent of the planet’s coral reef area and mass coral bleaching has been recorded in at least 83 countries and territories, the scientists said.
“The ongoing global coral bleaching event is the biggest to date. The previous record was during the 3rd global coral bleaching event, which occurred from 2014-2017, when 68.2 per cent of the world's reef area experienced bleaching-level heat stress. The 1st and 2nd global coral bleaching events occurred in 1998 and 2010, respectively,” the statement said.
Record high ocean temperatures have impacted the corals across the globe — Pacific, Atlantic and Indian oceans.
Coral reefs are deemed as the rainforests of the sea which support one third of the global marine species and nearly billion humans.
Coral bleaching is caused when the reef's water remains too hot for too long putting the corals under stress. The stress compels the corals to expel marine algae residing inside their tissues known as zooxanthellae.
These algae provide food and energy from the sun through photosynthesis, enabling the coral's growth and reproduction. Once the algae is expelled, the corals turn white exposing their skeleton called as bleaching, also making them vulnerable to diseases.
Corals can recover from bleaching in the conducive environment, but it can often take years or even a decade to recover depending on the damage caused. Prolonged and extreme exposure of heat due to heatwaves leads to coral mortality.
On December 15, 2023, NOAA Coral Reef Watch introduced a revised coral bleaching heat stress category system for its Bleaching Alert Area. These changes were necessitated owing to the extreme coral bleaching heat stress in 2023, in various parts of the planet especially the eastern tropical Pacific Ocean and Greater Caribbean.
Earlier, Bleaching Alert Level 2 was the ultimate category, but now new alert levels 3-5 have been added. These alerts address the risk of multi-species mortality for more than 50 per cent of the coral and risk of near complete mortality that is over 80 per cent of corals.
The Great Barrier Reef Marine Park authority recently informed that the reef is undergoing a sixth mass bleaching event and experienced widespread coral bleaching.
It is the second time the reef has experienced consecutive bleaching events, the first being reported in 2016-17.
“Prolonged exposure to higher-than-average water temperatures (marine heatwaves) this summer has caused widespread coral bleaching in the Far Northern and Northern regions of the Reef,” the authorities said.
In the worst affected areas, mortality has been documented on shallow-water corals at many inshore reefs, especially in the Palm and Family islands groups, the statement said.
Australia’s coral reefs suffered mass coral bleaching in 1998, 2002, 2016, 2017, 2020, 2022 and 2024.
In January, a report revealed that Southern Great Barrier Reef (GBR) experienced catastrophic coral bleaching in May 2024, with a staggering 44 per cent mortality rate in protected areas.
According to climate models, nearly every coral reef on the planet will experience bleaching events annually between 2040 and 2050.