Why Coral Reefs Are Approaching a Tipping Point
Coral reefs cover less than 1% of the ocean floor but support about a quarter of marine species. Increasingly frequent bleaching events are reducing their ability to recover.
Coral reefs cover less than 1% of the ocean floor, yet about 25% of marine species live in these ecosystems or depend on them at some stage of their life cycle.
Reefs also protect coastlines, support fisheries and contribute to the economies of many coastal regions.
Why corals bleach
Corals live in symbiosis with microalgae that provide much of their energy. When the water remains too warm, corals expel these algae and turn white. A bleached coral is not necessarily dead, but it is weakened.
It can recover if conditions become favourable again quickly enough.
An unprecedented global event
NOAA estimates that the fourth global bleaching event, which began in 2023, probably ended around mid-2025.
It was the most extensive ever observed: about 84.4% of the world's reef area experienced enough heat stress to cause bleaching across at least 83 countries and territories.
The central problem is now the repetition of shocks. Reefs affected in several consecutive years have less time to rebuild coral cover and diversity.
The Great Barrier Reef remains under pressure
During the 2025-2026 austral summer, the Great Barrier Reef faced several simultaneous pressures: prolonged heat, cyclones, flooding and outbreaks of crown-of-thorns starfish. Bleaching was regional in the north and more localised elsewhere.
Australian authorities stress that reef conditions remain highly variable between areas and that the full extent of the damage is still being assessed.
Protect locally, act globally
Reducing pollution, limiting overfishing, controlling predator species and restoring selected sites can improve local resilience. These measures cannot replace greenhouse-gas emissions reductions, which are the only way to limit the long-term increase in marine heat stress.
- Coral reefs support about a quarter of marine species on less than 1% of the ocean floor.
- The fourth global bleaching event was the most extensive ever observed.
- Local action strengthens resilience but cannot offset ocean warming.