The world’s coral reefs are facing an unprecedented crisis, with scientists warning that they have entered “uncharted territory” due to the most severe global bleaching event ever recorded.

According to the latest data from the U.S. government’s Coral Reef Watch, more than 80% of coral reefs worldwide have been exposed to heat stress intense enough to trigger bleaching since the event began in January 2023.

Coral bleaching, which occurs when corals expel the algae living in their tissues due to heat stress, turns vibrant reefs ghostly white and leaves them vulnerable to death. This ongoing event has affected reefs in at least 82 countries and territories, making it the most widespread bleaching event ever observed.

Often referred to as the “rainforests of the sea,” coral reefs support about a third of all marine species and provide food, livelihoods, and coastal protection to roughly a billion people globally. However, surging ocean temperatures—fuelled by climate change—are spreading rapidly across the Pacific, Atlantic, and Indian oceans, decimating coral populations.

The 84% of reefs exposed to bleaching-level heat in this ongoing fourth event far surpasses the previous record of 68% during the 2014–2017 event. Earlier events in 2010 and 1998 affected just 37% and 21% of reefs, respectively.

Notably, reefs once considered refuges due to their historical resilience have not been spared, according to Dr. Derek Manzello, director of Coral Reef Watch.

“The fact that so many reef areas have been impacted, including purported thermal refugia like Raja Ampat and the Gulf of Eilat, suggests that ocean warming has reached a level where there is no longer any safe harbour from coral bleaching and its ramifications,” he said.

Many regions have experienced back-to-back bleaching, including Australia’s Great Barrier Reef, which has now suffered six mass bleaching events in just nine years. Western Australia’s Ningaloo Reef has also seen record-breaking heat stress, while bleaching has recently been reported in Madagascar, the East African coast, and South Africa’s iSimangaliso Wetland Park.

Dr. Britta Schaffelke of the Australian Institute of Marine Science, who coordinates the Global Coral Reef Monitoring Network (GCRMN), called the current crisis unprecedented and warned that “reefs have not encountered this before.”

“With the ongoing bleaching it’s almost overwhelming the capacity of people to do the monitoring they need to do,” she said. “The fact that this most recent, global-scale coral bleaching event is still ongoing takes the world’s reefs into uncharted waters.

“[For] people who spend their entire working lives on monitoring and observing reefs and protecting reefs, and living alongside them and relying on them, seeing something like this must be devastating.

“Ecological grief is real. People who spend a lot of time under the water see it changing before their eyes,” she said.

The GCRMN is compiling global data for a 2026 report, but Schaffelke noted it would likely still underrepresent the full scale of the disaster.

Scientists across North and Central America were among the first to raise the alarm during the northern hemisphere’s summer of 2023, when extreme ocean temperatures triggered widespread bleaching in Florida, the Caribbean, and Mexico. Post-event surveys revealed devastating losses—Florida an average of one in five corals were lost, while one area in Mexico lost between 50% and 93% of its corals. In the remote Chagos Islands, a quarter of corals were killed by heat last year.

In early 2024, bleaching in Australia led to what scientists described as a “graveyard of dead corals” in the northern Great Barrier Reef. In one southern section, 40% of corals perished. The severity of 2023’s heat stress forced Coral Reef Watch to introduce three new threat levels to its bleaching alert system.

Melanie McField, founder of the Healthy Reefs for Healthy People initiative in the Caribbean, noted a disturbing silence across many reefs, an eerie sign of marine life disappearance.

“Bleaching is always eerie – as if a silent snowfall has descended on the reef … there is usually an absence of fluttering fish and an absence of the vibrant colours on the reef,” she said. “It’s an ashen pallor and stillness in what should be a rowdy vibrant reefscape.”

Meanwhile, Dr. Lorenzo Álvarez-Filip of Mexico’s National Autonomous University reported the collapse of critical reef-building corals such as elkhorn, which play essential roles in shoreline protection and biodiversity.

“Many of the coral colonies I knew well, and which had survived [a major disease] outbreak just a few years earlier, died in a matter of weeks.

“The feeling of impotence combined with the need to at least document what was happening made me very anxious – this was particularly hard when we were about to dive in sites where we knew there were big aggregations of susceptible corals. In almost all cases, we ended up with a very depressing feeling when we confirmed that all or nearly all the coral had died.”

Dr. Valeria Pizarro from the Perry Institute for Marine Science recounted witnessing catastrophic bleaching in the Bahamas in July 2023.

In mere days, thriving shallow reefs transformed into barren white landscapes. Restoration efforts suffered major setbacks as staghorn corals died en masse, and once-abundant sea fans and soft corals were wiped out.

 

——————————————————————————

At Natural World Fund, we are passionate about restoring habitats in the UK to halt the decline in our wildlife.

Donate now and join in the solution!