Like an overmatched boxer, the worlds coral reefs are being pummeled by climate change, and the onslaught may soon prove debilitating.
That was the main finding of a report released earlier this week by the Global Coral Reef Monitoring Network, whose partners include the United Nations Environment Programme (UNEP).
The report found that a succession of marine heatwaves over the last three decades has triggered the loss of at least 9.5 per cent of the worlds corals. Those that remain face a daunting future of potentially deadly underwater heat.
This report is another reminder that we are racing against time to protect these spectacular undersea cities from climate change, pollution and overfishing, said Susan Gardner, Director of UNEPs Ecosystems Division.
Heres a closer look at the main findings of the report Status of Coral Reefs of the World 2025 and what they mean for the future of corals.
First off, what are corals exactly?
Corals are tiny, tube-shaped animals that anchor themselves to the ocean floor or a stationary object, like a sunken ship. Cousins of jellyfish, they use stinging tentacles to catch prey floating on the currents.
Many coral polyps, as the animals are formally known, surround themselves with a hard calcium skeleton. When thousands of corals come together, they form reefs. These underwater cities are teaming with life. They cover less than 1 per cent of the ocean floor but support 25 per cent of marine species.
How do marine heatwaves harm corals?
Inside each coral are thousands of plant-like organisms called zooxanthellae. In one of the planets great symbiotic relationships, the corals provide the zooxanthellae with the carbon dioxide they need for photosynthesis and in return receive essential nutrients. (The micro-organisms also give corals their often eye-catching colour.)
But when ocean temperatures rise, corals become stressed and kick out their zooxanthellae, turning a ghostly white or gray. This process is known as bleaching. It doesnt kill corals outright. But it does leave them vulnerable to disease and starvation, said Sinikinesh Beyene Jimma, theChief of UNEPs Marine and Coastal Ecosystems unit.
What did the new report find?
The study surveyed nearly 37,000 coral sites in 120-plus countries. It compared coral coverage from 2020 to 2024 with the historical average from 1980 to 2009. The conclusion? At least 9.5 per cent of hard corals had disappeared. The studys authors say thats a conservative number, and the rate of coral retreat is likely higher.
But, importantly, the report found coral loss was not uniform around the world, and in some places, corals are rebounding.
What is causing the decline of corals?
In short, us. Human-induced climate change has triggered four major ocean heatwaves since 1998, each of which led to coral bleaching on a global scale.
Corals can recover from bleaching given enough time. But the rapid-fire nature of the recent heatwaves has impeded that process.
Its almost like a boxer absorbing a quick series of punches, said Gabriel Grimsditch, a Programme Management Officer with UNEP. The worlds corals are weakening with every heatwave, and theyre not getting the time they need to find their legs.
Climate change isnt the only problem, though. Pollution, overfishing and coastal development are making it harder for corals to weather ocean heatwaves.
How far apart do bleaching events need to be for corals to recover?
The report found that if bleaching events happened every 10 years, most corals would probably have time to recover, and the coral coverage globally would remain about the same as the historical average. But if bleaching events continue to happen every five years or so, corals will continue to decline.
What does the future hold for corals?
Right now, coral reefs are in a perilous position. Humans continue to churn out greenhouse gases at record levels, driving up the average global temperature. Even if humanity holds warming to that level, between 70 and 90 per cent of reef-building corals are expected to die. If warming reaches 2C above pre-industrial times, 99 per cent of corals will perish. Government policies have the planet on track for at least 1.8C of warming.
But there are signs of hope. The seas around South Asia and the Western India Ocean saw a rebound in coral coverage, according to the report.
[The report] shows us that coral reefs can and do recover when we invest in their protection and restoration, said UNEPs Gardner. Healthy reefs support marine life, food security and livelihoods, and a better future for coastal communities.
If we cant turn the tide, what would the loss of coral reefs mean for people and the ocean?
It could be devastating. Corals support 25 per cent of marine life, including thousands of fish species. When corals die, theyre often replaced by seaweed, which causes biodiversity to plummet. That would have a dramatic impact on communities around the world. More than 1 billion people rely on corals for food, jobs, recreation and protection from storm surges.
We dont want to contemplate a future without corals, said UNEPs Grimsditch.
Can anything be done to protect corals?
Yes. First, humanity needs to stop burning fossil fuels and limit global warming. Scientists estimate at least 90 per cent of warmth is absorbed by the ocean, driving marine heatwaves.
At the same time, countries need to reduce local stressors, like overfishing and pollution, and make sure tourism doesnt harm reefs. This can help give them the breathing room they need to recover.
To do that, the world needs to invest more in programmes like the Global Fund for Coral Reefs, said Beyene Jimma. The fund provides financial support to coral conservation projects in more than 20 developing nations. It is also a partner of the Global Coral Reef Monitoring Network, which issued the new study.
This report, like so many others before it, makes clear that we need to start getting serious about climate change, less we lose the incredible resources that are coral reefs, said Beyene Jimma.
The Global Coral Reef Monitoring Network is a network of scientists and other experts that monitor the condition of coral reefs throughout the world. A part of the International Coral Reef Initiative, its science is designed to support the conservation and management of coral reefs. The networks partners include the United Nations Environment Programme and the Global Fund for Coral Reefs.
Written by: Andrew Raven
Reviewed by: Gabriel Grimsditch, Sinikinesh Beyene Jimma, Doreen Robinson
