Coral reefs are more resilient than previously thought
Coral reefs are one of the key symbols of the climate crisis. Their demise due to ocean warming is being captured on video and documented by scientists and journalists around the world. The picture seemed clear: the reefs are dying, and it is almost impossible to stop it.
A new study offers a more complex and unexpectedly encouraging perspective. Scientists have compiled the most detailed map of coral reefs in history and found that around a third of them — 166,000 square kilometres — are resilient enough to survive severe climate shocks. This is three times more than was previously known. The findings were presented at the Our Ocean conference in Mombasa.
An important caveat: the study has not yet undergone independent peer review. The authors also emphasise that the good news does not negate the main point: reducing carbon emissions remains the most crucial condition for the long-term preservation of reefs. And two-thirds of the reefs remain vulnerable.
Details
First, let’s look at what happens to corals when the water warms up. When the water temperature rises by even one or two degrees, corals experience stress and expel the algae from their tissues that give them their colour and provide them with nourishment. The coral turns white — this is called bleaching. If the stress persists for a long time, the coral dies.
Large-scale bleaching events have become almost an annual occurrence. The Intergovernmental Panel on Climate Change (IPCC) has warned that a rise of 1.5°C above pre-industrial levels could kill between 70 and 90 per cent of all reefs, and a rise of 2°C could kill up to 99 per cent.
New research by the Wildlife Conservation Society (WCS) and Macquarie University in Australia does not refute these figures, but it does refine the picture. It turns out that reefs are not all the same: some are located in naturally cool waters, others have evolved to adapt to the heat, and others recover from shocks faster than the rest. It is precisely these reefs that the authors refer to as ‘climate-resilient’.
New mapping technology has produced a map 10,000 times more detailed than any previous one. It is this that has enabled the discovery of three times as many resilient reefs as were known from the pioneering 2018 study. More than half of them are concentrated in Australia, the Bahamas, Cuba, Indonesia and the Philippines.
“The response of corals to heat events is much more nuanced than we previously thought,” says Stacey Jupiter, Executive Director of Marine Conservation at WCS.
The authors compare such reefs to ‘living seed banks’ — reservoirs of life from which the recovery of wider ecosystems can begin following climate shocks.
Why this matters
The problem is that only 28% of these resilient reefs are currently under active protection. The rest are vulnerable not so much to global warming as to threats that humans can control right now: destructive fishing, water pollution, and uncontrolled tourism.
This changes the logic of nature conservation. If we know exactly which reefs have the best chance of survival, protecting them becomes the number one priority. Rather than spreading our efforts evenly across all the world’s reefs, we should focus on those that have a real chance of survival.
The story of the Kenyan island of Wasini-Mkwiro shows that this works. Local fishermen weigh and record every catch. Volunteer patrols ensure that no one fishes using prohibited methods. Residents plant seaweed and mangrove trees, and clear away rubbish. In 2024, following a large-scale bleaching event, coral cover here fell from 44% to 27% — but had recovered to 40% just one year later. In 2021, this marine park became the first in Kenya to receive the Gold Level Blue Park Award.
Background
Coral reefs cover less than 1% of the world’s oceans but support around a quarter of all marine species. For hundreds of millions of people worldwide, they are a source of food, income from tourism and protection for coastlines against waves.
The problem of bleaching has worsened in recent decades alongside the acceleration of global warming. The most widespread bleaching event in recorded history occurred in 2024 and affected reefs around the world.
The current study was funded by the Bloomberg Ocean Initiative and builds on a methodological breakthrough in remote sensing: new technologies allow us to distinguish between coral types and seabed topography with unprecedented accuracy. This opens up the possibility not only of tracking the decline of reefs, but also of specifically identifying those that have a chance of survival.
However, scientists are unanimous: even the most resilient reefs will not withstand unchecked warming.
“Reducing carbon emissions remains the most important thing if we want coral reefs to exist in a hundred years’ time,” says coral scientist Clint Oakley from Victoria University in Wellington.
Source
The study was conducted by the Wildlife Conservation Society (WCS) in collaboration with Macquarie University (Australia). The lead author is Kyle Zavada. The work was funded by the Bloomberg Ocean Initiative and was under review at the time of publication. The findings were presented at the Our Ocean conference in Mombasa, Kenya.