Why in News?
The seventh Status of Coral Reefs of the World report, released by the Global Coral Reef Monitoring Network (GCRMN) on 31 August 2026, has warned that coral bleaching events are becoming more frequent, leaving reefs with less time to recover from severe heat stress.
Key Findings
- Global hard coral cover has declined by around 9.5% compared with the 1980–2009 reference period.
- Major disturbances are now occurring every 4–6 years, compared with roughly once a decade earlier.
- In 2024, 87% of reefs experienced unprecedented heat stress, while over 40% faced heat stress linked to bleaching and mortality.
- More than 27% of global reef areas experienced severe bleaching-level heat stress on at least four occasions between 2019 and 2025.
- Sea-surface temperatures over coral reefs increased by about 0.81°C between 1985 and 2025.
Major Driver: Marine Heatwaves
- Marine heatwaves, intensified by human-induced climate change, have become the strongest global driver of coral-cover decline.
- Prolonged heat stress causes corals to expel their symbiotic algae, known as zooxanthellae, resulting in coral bleaching. Prolonged bleaching can lead to coral mortality.
Fourth Global Mass Bleaching Event
- The fourth global mass coral bleaching event began in 2023 and reached unprecedented levels in 2024.
- Global hard coral cover declined by 8.9% between 2023 and 2024, the largest single-year relative decline recorded in the report.
What is Coral Bleaching?
- Coral bleaching is a phenomenon in which corals turn white due to environmental stress, mainly because of unusually high sea temperatures.
- Corals have a symbiotic relationship with tiny algae called zooxanthellae, which provide them with food through photosynthesis and give them their colour. Under stress, corals expel these algae, exposing their white calcium carbonate skeleton.
Note: Bleached corals are not immediately dead. They can recover if favourable conditions return, but prolonged stress can cause coral death.
Causes of Coral Bleaching
- Rising sea temperatures: the major cause of mass coral bleaching.
- Marine heatwaves: prolonged periods of unusually warm ocean temperatures.
- Ocean pollution: chemicals, sewage and other pollutants can stress corals.
- Poor water quality: excessive nutrients and sediment can damage coral reefs.
- Excessive sunlight/UV radiation: can increase stress during periods of high temperature.
- Sudden temperature changes: both unusually warm and unusually cold water can trigger bleaching.
How to Prevent/Reduce Coral Bleaching
- Reduce greenhouse gas emissions to limit global warming and ocean heating.
- Control marine and coastal pollution and improve water quality.
- Protect coral reef ecosystems through Marine Protected Areas (MPAs).
- Reduce local stresses such as overfishing, destructive fishing and coastal development.
- Restore damaged reefs through coral restoration and reef rehabilitation programmes.
- Strengthen monitoring and research to detect bleaching early and improve coral resilience.
