A silent crisis beneath the waves: Global coral reefs suffer historic bleaching event

Department of Research, Studies and International News 23-04-2025

The world’s coral reefs are undergoing an unprecedented environmental crisis, as over 80% have been affected by a mass bleaching event, the most severe recorded in history. Marine scientists and conservationists warn that coral ecosystems are now experiencing levels of stress never seen before, pushing them into uncharted and dangerous territory.

According to data from the U.S. National Oceanic and Atmospheric Administration’s Coral Reef Watch, coral reefs in at least 82 countries and territories have endured prolonged ocean heat stress since January 2023, resulting in widespread bleaching. These vibrant underwater structures, often called the “rainforests of the sea,” support roughly a third of all marine species and sustain the livelihoods of around a billion people globally.

However, rising sea temperatures, driven by human-induced climate change, have ravaged reefs across the Pacific, Atlantic, and Indian Oceans. The percentage of reefs affected in this current, fourth global bleaching event stands at 84%, a stark rise compared to previous episodes: 68% during 2014–2017, 37% in 2010, and 21% in the inaugural 1998 event.

Even areas once thought to be refuges, such as Indonesia’s Raja Ampat and the Gulf of Eilat, have not been spared. Dr. Derek Manzello, head of Coral Reef Watch, stressed that the absence of safe havens signals a worrying shift: “We are reaching a point where nowhere in the ocean is safe from bleaching. The warming is now too widespread and severe.”

Australia’s Great Barrier Reef, the largest reef system on Earth, has now experienced its sixth mass bleaching event in under a decade. Further west, reefs along Western Australia’s Ningaloo coast recently endured record-breaking heat stress. Across the Indian Ocean, coral systems off the coasts of Madagascar, South Africa, and other East African nations are facing similar destruction.

Dr. Britta Schaffelke of the Australian Institute of Marine Science and coordinator of the Global Coral Reef Monitoring Network (GCRMN) described the event as “unprecedented.” She highlighted that the scale of bleaching has overwhelmed scientists’ ability to monitor and document the damage effectively. “We are facing a global phenomenon that exceeds previous records. For those who study and depend on coral reefs, the loss is deeply personal.”

Schaffelke also spoke about the emotional toll on researchers witnessing the degradation of ecosystems they have studied for decades. “There’s a real sense of ecological grief. Divers and scientists are watching living coral turn into ghostly skeletons before their eyes.”

Surveys following last year’s peak heat waves revealed dramatic losses. Florida saw roughly 20% of its coral populations wiped out, while sections of Mexico’s Pacific coast lost up to 93% in some areas. In the Indian Ocean, nearly a quarter of coral in the remote Chagos Archipelago perished due to extreme heat. The Great Barrier Reef’s northern reaches also became a graveyard, with nearly 40% coral mortality in some parts by early 2024.

This unprecedented event even forced Coral Reef Watch to expand its bleaching alert system by adding new, more extreme levels to accommodate the extraordinary heat stress levels.

Melanie McField, founder of the Healthy Reefs for Healthy People initiative, described the reefs’ transformation in chilling terms: “It’s like a ghost world, the usual colors and marine life are gone, replaced by a haunting silence and pale corals. It feels like snowfall underwater.”

In Mexico, Dr. Lorenzo Álvarez-Filip reported the heartbreaking loss of large reef-building coral colonies that had withstood previous diseases, only to perish rapidly from the heat. “Knowing what awaited us at dive sites was unbearable, but documenting it was essential.”

Dr. Valeria Pizarro from the Perry Institute for Marine Science also witnessed sudden devastation in the Bahamas, where vibrant reefs turned white seemingly overnight, and entire coral species used in restoration efforts succumbed quickly to the heat. “It looked as though the coral were melting,” she recalled.

Scientists globally are urging world leaders to translate climate pledges into immediate action. “It’s no longer enough to talk, the transition to clean energy must become reality,” said Pizarro. “The reefs can’t wait.”