See How Much Corals Have Declined in Just 40 Years

The world’s coral reefs are in dire shape, according to a new report.

Hard corals, as opposed to soft corals, form the stoney bases on which reefs typically grow. In the past 40 years, they have declined by nearly 10 percent and the amount of time they have to recover from heat waves is shrinking.

“Corals are declining globally and climate change is now the main driver of this change,” says marine ecologist Jérémy Wicquart, co-editor of the Global Coral Reef Monitoring Network’s Status of Coral Reefs of the World: 2025 report.

The findings are based on 21.1 million observations from 87,299 surveys across 36,886 reef sites in 120 countries and territories, between 1980 and 2024. More than 600 partners shared their data.

When scientists assessed coral cover between 2020 and 2024, it had declined by 9.5 percent, compared to coral reef cover assessed from 1980 to 2009. This documented decline, and continued ocean warming, suggests many more of the world’s reefs could be lost. A new United Nations report found that the world is virtually guaranteed to soon be 1.5°C warmer than it was before the Industrial Revolution. At this temperature, previous reports show as much as 90 percent of the world’s reefs could disappear by 2050.  

How Do Hot Waters Affect Corals?

Corals are living creatures. “A lot [of hard corals] just look like a rock, but they are indeed alive, and they're really quite spectacular animals,” says Molly Asbury, a coral ecologist at National Geographic’s Pristine Seas—one of the organizations that contributed to the report.

Tiny microalgae nestle inside the small polyps that stem from coral branches. These algae gives corals most of their food, and it’s the algae’s pigment that makes coral turn bright, vivid colors.

But because corals stay rooted in one spot, they can’t escape local threats to their environment. A temperature increase of just one or two degrees Celsius can cause algae to produce toxic chemicals and, when this happens, “the coral expels the algae as a mechanism to try to protect itself,” explains Asbury.

Without the algae, the coral turns white—a process called coral bleaching—and can die if stressful conditions don’t abate.

The Impact of Marine Heatwaves

The report highlights four global bleaching events between 1998 and 2024, each followed by a steep coral decline of up to 9.9 percent. The most recent bleaching event, which likely ended in mid-2025, has not yet been fully analyzed.

Reefs can bounce back when they have a period of respite. “As soon as the conditions become favorable, corals can recover,” says Wicquart. Between 2017 and 2019, hard coral cover increased by around six percent following bleaching.

“What struck me most was seeing both vulnerability of coral and resilience,” says Wicquart. “You can clearly see the losses associated with global bleaching events, but you can also see coral cover increasing.”

Worryingly, recovery windows are shrinking, giving corals less time to recover from extreme heat waves. In many of the regions the report analyzed, heat waves were previously observed every decade, but since 2010 they now occur around every five years.

If annual marine heatwaves become the new normal, “it's quite troubling for coral reefs,” says ‪Thomas Dallison, the report’s co-editor and senior project manager at Blue Pangolin Consulting.  

The brewing super El Niño will likely cause even hotter waters next year. El Niño is a natural phenomenon of weakening winds across the equator that increases sea surface temperatures in the Pacific and pushes temperatures up globally. They typically happen every two to seven years. “Each time there is a strong El Niño, there is usually a global bleaching event,” says Wicquart.

If El Niño continues pushing water temperatures up, the stress could kill the corals still recovering from elevated temperatures in the first half of 2026.

Saving Reefs From Extinction

Coral reefs are habitat for endangered species, provide nurseries for lucrative fish stocks, and blunt the force of hurricanes. When they are lost, “it's those that depend on them that will pay the price,” says Dallison.

But experts say it’s not too late to act. “Local protection matters even more than maybe it did before,” says Beverley French, a postdoctoral researcher at Scripps Institution of Oceanography.

Reefs can make a remarkable comeback when protected from pressures such as pollution and unsustainable fishing. For example, when fishing removes too many algae-eating fish from the ecosystem, corals must compete with algae for space. Healthy populations of these fish “can chomp down that algae, which gives coral a foothold so that it can grow,” says French.

Some data suggests that most tropical reefs will be lost by 2050, but the report highlighted strong regional variability. In South Asia and the Western Indian Ocean, reefs recovered—showing that it is possible.

“It's in our hands, basically, to save reefs,” says Dallison. “It's incredibly alarming, but it's not all doom and gloom for coral reefs.”