The 2023 to 2025 global coral bleaching event was announced in April 2025 as the most extensive in recorded history, impacting 84% of the world’s coral reef ecosystems across 82 countries. Scientists who have spent careers studying coral reefs described it as unprecedented. A widely used bleaching prediction platform had to add three entirely new warning levels to its scale because the existing categories were no longer sufficient to describe what was happening.

This is not a warning about a future crisis. It is a description of the present one.

The Scale of the 2023-2025 Global Bleaching Event

Prior to the 2020s, three global bleaching events had been recorded. The first in 1998 affected 21% of reefs. The second in 2010 affected 37%. The third from 2014 to 2017 affected 68%. The fourth, still ongoing as of 2026, has affected 84% and shows no clear sign of ending. Each successive event has been larger and more damaging than the last.

In the West Philippine Sea, research by the University of the Philippines Marine Science Institute found that sites experiencing severe bleaching during the 2024 peak had declined by 51 to 59% in hard coral cover in just two years. That is not gradual decline. That is collapse.

The Threats in Detail

Climate Change and Ocean Warming

Coral bleaching is triggered when ocean temperatures rise just one to two degrees Celsius above the seasonal maximum for an extended period. As greenhouse gas emissions continue to warm the planet, ocean temperatures are rising faster than coral reefs can adapt. Scientists predict that annual mass bleaching events could occur on the majority of the world’s reefs by 2050 under current emissions trajectories.

Ocean Acidification

As the ocean absorbs carbon dioxide from the atmosphere, seawater becomes more acidic. This process reduces the availability of carbonate ions that coral polyps need to build their calcium carbonate skeletons. Reefs are literally dissolving faster than they can grow in many locations. Acidification does not cause bleaching directly but weakens reef structures and slows recovery after bleaching events.

Destructive Fishing

Dynamite fishing and cyanide fishing have caused catastrophic physical damage to reef formations across Southeast Asia. A single dynamite blast can destroy decades of coral growth in seconds. Despite being illegal throughout the Philippines, these practices continue in many areas because of inadequate enforcement capacity and extreme economic pressure on fishing communities.

Coastal Development and Runoff

Urban and agricultural development in coastal areas generates runoff containing sediments, fertilizers, and pollutants that smother coral polyps, block sunlight, and create algae blooms that outcompete coral for space on the reef. In Cebu, rapid coastal urbanization around the greater Cebu City area has degraded reef systems within swimming distance of populated shorelines.

Overfishing

The removal of key reef species disrupts the ecological relationships that healthy reefs depend on. Parrotfish and surgeonfish graze the algae that would otherwise overgrow coral. Large predators maintain prey population balances. When these species are removed by unsustainable fishing, reefs shift from coral-dominated to algae-dominated systems that recover slowly if at all.

What This Means for the Philippines

Studies of Philippine reef status show the national average hard coral cover at approximately 22.8%, with the loss of about a third of reef corals over the past decade. These are national averages. In heavily impacted areas, the declines are far more severe.

Moalboal in Cebu, famous among divers for its sardine run and wall diving, has faced pressure from tourism growth, runoff from inland development, and the 2024 bleaching event. Malapascua, known worldwide for thresher shark dives at Monad Shoal, was hit hard by Typhoon Haiyan in 2013 and has faced ongoing recovery challenges. These are not abstract statistics. They are places that real divers love and that real communities depend on.

Clarisa Strohmeyer is the Founder and Executive Director of Reef Without Borders, a Houston-based nonprofit dedicated to coral reef restoration in the Philippines and across the Indo-Pacific. Learn more at reefwithoutborders.org/