Create a list of articles to read later. You will be able to access your list from any article in Discover.
You don't have any saved articles.
Climate change threatens nearly half of all corals with extinction
Over 40% of reef-building corals are at risk of being wiped out in the coming decades.
An update to the Red List of corals shows that rising temperatures are pushing many species to the brink, alongside disease, pollution and unsustainable fishing.
Scientists have sounded the alarm for the health of the world’s coral reefs.
An update to the Red List of corals by the International Union for the Conservation of Nature (IUCN), announced at the COP29 climate summit, revealed that 44% of coral species are now threatened with extinction. This is a sharp increase from the previous assessment, published in 2008, which found a third of corals were in danger of being lost.
Climate change is the leading cause of the declines, with high temperatures causing corals to eject the photosynthetic algae that live in their tissues. These events, known as bleaching, are becoming more extreme and more frequent, and causing mass die-offs in reefs across the world.
The IUCN’s Director General, Dr Grethel Aguilar, has called for strong action to limit greenhouse gas emissions as the best option to protect these vital species.
“This global coral assessment vividly illustrates the severe impacts of our rapidly changing climate on life on Earth and drives home the severity of the consequences,” she says. “Healthy ecosystems like coral reefs are essential for human livelihoods – providing food, stabilising coastlines, and storing carbon.”
“The protection of our biodiversity is not only vital for our wellbeing but crucial for our survival. Climate change remains the leading threat to reef-building corals and is devastating the natural systems we depend on. We must take bold, decisive action to cut greenhouse gas emissions if we are to secure a sustainable future for humanity.”
Corals get their colour from the photosynthetic algae that live inside them, as part of a relationship which has lasted for over 380 million years. © Alexandre.ROSA/ Shutterstock
How endangered are corals, and why are they important?
The results of the latest Red List are the latest reminder of the dangers that reef-building corals face, with the animals having become more threatened with every reassessment of their health.
While Red List assessments have changed over the past 30 years, it’s estimated that just 13 coral species were considered Vulnerable, Endangered or Critically Endangered in the 1990s. By the time of the next assessment in 2008, this figure had risen to 231.
It has now risen again, by more than 100, meaning almost half of all corals are at significant risk of extinction. This makes corals proportionately more endangered than all the major animal groups on land, including amphibians, mammals and reptiles.
If these coral species do become extinct, their loss would cause major changes for life in the oceans. Coral reefs support around a quarter of all marine life, and so it’s likely that coral extinctions could cause losses among fish, crustaceans and many other groups.
The loss of coral reefs would also remove an important nursery habitat for fish, as the hard skeletons provide a safe area for small fish to grow up in, away from large predators. Fewer nursery habitats would likely mean fewer fish, impacting both predator populations and fisheries.
The economic impact of coral extinctions goes much further than fishing, with reefs estimated to prevent billions of pounds worth of damage from flooding and erosion every year by breaking up waves. It’s also likely tourism would suffer, cutting off a vital source of income for many communities.
The most at-risk reefs are in the Atlantic, where half of all species are at risk of extinction and a quarter are Critically Endangered. In a separate paper, published in PLOS One, researchers have examined the threats facing these corals in particular.
The staghorn coral Acropora cervicornis is found in the Atlantic, and is considered Critically Endangered under the most recent Red List. © Alberto Rodríguez-Ramírez
Why are Atlantic corals so threatened?
While the vast majority of reefs are found in the Indian and Pacific Ocean, around 10% are found in the Atlantic. These corals are very distinct from their relatives, having been separated from other corals by the joining of North and South America over three million years ago.
In total, 85 shallow-water coral species live in the Atlantic, with the most important hotspots found in the Caribbean and off the coast of Brazil. As study co-author Dr Nadia Santodomingo explains, the limited ability of these species to respond to the threats facing them means these reefs are more vulnerable to collapse.
“Atlantic corals have been hit the hardest by reef decline,” says Nadia, a Curator of Fossil Cnidaria at the Natural History Museum. “They’re facing a perfect storm of threats, of which climate change is just one part.”
“These corals are being significantly impacted by overfishing, pollution and coral diseases which are more prevalent in the Atlantic than in other regions. As a result, I wasn’t surprised to see the results of the IUCN assessment.”
Disease has perhaps had the most dramatic impact on Atlantic corals, devastating not only the region’s corals but also the animals they depend on. An unknown illness is suspected to have killed as much as 98% of the Caribbean’s long-spined sea urchins in the 1980s, meaning these grazers couldn’t prevent algae from dominating many reefs.
New diseases are continuing to emerge, with stony coral tissue loss disease first detected in 2014. The illness has spread rapidly throughout the Caribbean, killing as many as 94% of all infected corals.
Rising temperatures are also an increasing threat, with bleaching just the tip of the iceberg. Higher levels of carbon dioxide are making the ocean more acidic, making it harder for corals to grow their calcium carbonate skeletons. Climate change has also been linked with rising numbers of hurricanes in the region, which are washing away centuries-old reefs in a matter of hours.
While the PLOS One study raises plenty of cause for concern, it also notes some reasons to be hopeful. After the devastating declines of the 1970s and 1980s, the researchers found that the fall in Atlantic coral cover appears to be getting smaller.
To support these green shoots of recovery, further research needs to be taken to understand how corals can adapt to the challenges that face them. As Dr Beth Polidoro, a co-lead author of the paper, explains, this must go hand in hand with urgent action to combat climate change and the other threats facing coral.
“We need to drastically cut greenhouse gas emissions alongside action to address local threats if we want to give coral reefs a chance to survive,” says Beth. “By acting now, we can slow the pace of ocean warming and broaden the window of opportunity for corals to potentially adapt and survive in the long term.”
