'I thought it was just a rock': Bleached coral spotted worldwide signals worst-ever ecological crisis

Bleached coral: a signal of ecosystem collapse

Coral reefs are a familiar sight beneath the ocean's surface — each species displaying its own distinct color, painting the seafloor in vivid hues.

But coral that has turned ghostly white tells a very different story. It may signal not only that the coral itself is on the verge of death, but that the broader marine ecosystem is beginning to unravel.

Coral is particularly vulnerable to heat. When seawater temperatures rise, this "bleaching" phenomenon occurs.

Coral reefs support the survival of one-third of all marine species and serve as a cornerstone of ocean ecosystems. About 1 billion people worldwide benefit directly or indirectly from the economic activities they sustain.

Last year, 84 percent of coral populations globally experienced heat stress severe enough to cause bleaching. Rising sea temperatures have pushed the vast majority of the world's coral to the brink of death.

The greater concern lies ahead. An El Niño event is forecast to develop globally this year, driving a prolonged rise in sea surface temperatures — raising fears that bleaching damage could become catastrophic.

Coral are animals that live in the sea. Tiny coral polyps cluster together to form colonies, and some secrete hard calcium carbonate skeletons. A coral reef is the underwater terrain and ecosystem built up over centuries as those corals grow, die and accumulate layer by layer.

When coral is subjected to thermal stress from abnormally warm water, it expels the symbiotic algae living inside its tissues, exposing the white skeleton beneath — a process known as bleaching. When bleaching leads to mass die-offs, the seafloor terrain and the ecosystem it supports are destabilized along with it.

Mass bleaching is not a new phenomenon, but it has accelerated sharply. The first global coral bleaching event occurred in 1998, threatening coral reefs across 21 percent of the world's reef area. Subsequent events in 2010 and from 2014 to 2017 affected 37 percent and 68 percent of reef areas, respectively.

The largest bleaching event on record unfolded between 2023 and 2025. According to data released by the International Coral Reef Initiative (ICRI), 84 percent of the world's coral reef area experienced bleaching-level heat stress between 2023 and March 2025. Damage was reported in 83 countries and territories.

This month, the National Oceanic and Atmospheric Administration (NOAA) and the Global Coral Reef Monitoring Network (GCRMN) said the fourth global coral bleaching event had concluded by mid-2025. That does not mean the coral has recovered. It means satellite-measured heat stress across the globe has eased and large-scale bleaching reports have declined.

The fact that bleaching occurred across most of the world's reef area does not automatically mean the coral is dead. If seawater cools and conditions stabilize, some coral can reabsorb symbiotic algae and survive. The danger is that prolonged high temperatures, or repeated bleaching events, can lead to mass mortality.

In other words, if seawater remains warm for an extended period, bleaching can translate into real ecological damage. Global temperatures continue to climb, and the oceans — which absorb roughly 90 percent of the excess heat the planet receives — are warming at an accelerating pace.

Projections cited by the Intergovernmental Panel on Climate Change (IPCC) and the UN Environment Programme (UNEP) indicate that even a 1.5-degree Celsius rise in average global temperatures could reduce coral reefs by 70 to 90 percent, while a 2-degree rise could result in a 99 percent loss. Yet recent global average temperatures have already been hovering around or above the 1.5-degree threshold above pre-industrial levels.

That means 70 to 90 percent of the world's coral reefs are on the edge of collapse — and in some regions, that scenario is already playing out. According to the Australian Institute of Marine Science (AIMS), the Great Barrier Reef recorded the largest annual decline in coral cover ever observed during 2024 and 2025. One of the world's most celebrated reef ecosystems has buckled under repeated bouts of extreme heat.

What matters most now is giving coral that has just endured a mass bleaching event time to recover. But the outlook for sea surface temperatures this year is alarming, as an El Niño event — a natural climate pattern that drives global temperature increases — is forecast to develop.

NOAA said El Niño conditions emerged in June 2026 and are expected to intensify through the Northern Hemisphere winter. El Niño is a natural climate oscillation that raises sea surface temperatures across the central and eastern Pacific. It is now occurring on top of oceans already warmed by long-term climate change.

For coral, the problem is not simply that water temperatures are rising. Elevated temperatures are persisting longer, meaning the next bout of heat stress may arrive before the coral has had any chance to recover.

Scientists view coral bleaching with such alarm because reefs play an outsized role in marine ecosystems relative to the space they occupy. UNEP notes that coral reefs cover less than 1 percent of the ocean floor yet support at least 25 percent of all known marine species.

Their economic importance is equally significant. According to the UN Food and Agriculture Organization (FAO), fish from coral reef areas account for 10 percent of global fisheries catch. The protective structure reefs provide makes reef zones far more productive than other marine environments.

ICRI estimates that about 1 billion people worldwide benefit directly or indirectly from coral reefs. Should coral disappear due to climate change, the resulting food and job shortages could generate economic losses of up to $500 billion by 2100, according to projections.

Against this backdrop, calls are growing for international investment in coral restoration. Efforts are underway — including coral aquaculture and the search for heat-resistant species. Recently, coral with unusually high resilience was discovered in a mangrove lagoon near Australia's Great Barrier Reef, raising hopes for what researchers have dubbed "super coral."

But meaningful policy-level action has yet to materialize. Last year, under the Kunming-Montreal Global Biodiversity Framework (KM-GBF), many countries that host coral reefs submitted biodiversity targets — yet none set specific goals for coral reef protection.

"At a time when many experts emphasize that this decade is a critical juncture for the future of coral reefs, a serious gap exists between global goals and actual national action," ICRI said, urging governments to "develop national coral reef strategies and action plans."