Source: Down To Earth
Context: The Global Coral Reef Monitoring Network (GCRMN) released the 7th Status of Coral Reefs of the World report — finding near-annual bleaching stress, a 9.5 per cent decline in global hard coral cover, and recovery windows shrinking to just 4–6 years.
Key Findings
- Global hard coral cover has declined by about 9.5% compared with the 1980–2009 reference period.
- There has been a pronounced decline since 2010.
- 2023–24 witnessed the 4th Global Mass Coral Bleaching Event.
- In 2024, around 87% of coral reefs experienced unprecedented heat stress.
- 42.6% of global reefs experienced heat stress of ≥8°C-weeks, a level associated with widespread bleaching and mortality.
- In 2025, this figure was 27.4%.
- Global hard coral cover declined by 8.9% between 2023 and 2024, the largest single-year relative decline recorded.
Coral Reefs
- Coral reefs are underwater ecosystems built mainly by tiny marine animals called coral polyps.
- They are found mostly in warm, shallow, clear and nutrient-poor tropical seas.
- Coral polyps secrete calcium carbonate (CaCO₃), which forms the hard reef structure.
How coral reefs form
- Coral polyps live together in colonies.
- They build calcium-carbonate skeletons.
- When corals die, their skeletons remain.
- New corals grow over these structures.
- Over thousands of years, this creates large coral reefs.
Why coral reefs are important
- Biodiversity: Support around 25% of marine species despite covering less than 1% of the ocean floor.
- Coastal protection: Reduce the impact of waves, storms and erosion.
- Livelihoods: Support fisheries, tourism and coastal communities.
- Carbon and nutrient cycling: Contribute to important marine ecosystem processes.
- Food security: Provide fishing grounds for millions of people.
Major threats
- Ocean warming → coral bleaching
- Ocean acidification → makes calcium-carbonate formation difficult
- Marine pollution
- Overfishing
- Sedimentation
- Coastal development
- Destructive fishing practices
What Coral Bleaching Is
- When water becomes unusually warm, corals become stressed.
- They expel their zooxanthellae.
- The coral loses its pigments and primary nutrient supply
- Turning bone-white, leaving the calcified skeleton vulnerable to disease and starvation
- If stressful conditions continue for a long time, the coral may die.
