Why in News?
- The Great Barrier Reef has experienced its largest decline in coral cover in nearly four decades, largely due to severe coral bleaching, cyclones and outbreaks of crown‑of‑thorns starfish.
What Is Coral Bleaching?
- Corals live in symbiosis with microscopic algae called zooxanthellae. These algae provide corals with food via photosynthesis and give them their colour.
- When stressed—typically by increased sea temperatures, pollution or excessive sunlight—corals expel the algae. This leaves the coral white or “bleached” and deprived of its main food source.
- Bleached corals can recover if stress conditions ease quickly and algae return. Prolonged stress, however, leads to coral death.
Causes of the Current Bleaching Event
- Rising sea temperatures due to climate change and events such as El Niño.
- Pollution from agricultural runoff, which encourages algal blooms and lowers water quality.
- Excessive solar irradiance during marine heatwaves.
- Extreme low tides that expose shallow corals to air and heat.
- Storm damage and predation by crown‑of‑thorns starfish.
Process of Bleaching
- Under normal conditions, corals and algae live in a mutually beneficial relationship.
- Environmental stress disturbs this balance, prompting the coral to expel the algae.
- The coral’s transparent tissue reveals its white skeleton, leaving it weak, energy‑deprived and more susceptible to disease.
- If conditions improve, algae return and the coral recovers; if not, the coral dies and reef ecosystems degrade.
Implications
- Ecosystem collapse: Coral reefs support roughly 25 % of marine species. Their decline threatens biodiversity.
- Economic losses: Fisheries, tourism and coastal protection services provided by reefs are at risk.
- Climate feedback: Dead reefs store less carbon and reduce natural defences against waves and storms.
Conclusion
The bleaching of the Great Barrier Reef highlights the urgency of addressing climate change, pollution and overfishing. Protecting reefs requires global and local action to reduce emissions and improve marine management.