GS Paper 1 10 marks · 150w 9 min Medium
Assess the impact of global warming on the coral life system with examples.
Subtopic: Geography · global warming, coral bleaching and reef ecosystems
How to structure your answer
Introduction (corals as narrow-tolerance ecosystems dependent on symbiotic algae) → thermal stress and mass bleaching → ocean acidification and allied stresses → global and Indian examples → cascading ecological and human impacts → Conclusion
Detailed model answer
186 words · target 150 words · 9 min
Reef-building corals live within a narrow temperature band (about 23-25°C) and depend on symbiotic zooxanthellae algae for colour, nutrition and calcification, which makes them acutely sensitive to global warming.
Pathways of impact
- Thermal stress and bleaching: when sea-surface temperature stays roughly 1°C above the seasonal maximum for weeks, corals expel their zooxanthellae, turn white and, if stress persists, die.
- Ocean acidification: higher atmospheric CO2 dissolves into seawater, lowering pH and aragonite saturation, so corals struggle to build their calcium-carbonate skeletons.
- Allied stresses: sea-level rise reduces light, and warmer waters bring stronger cyclones and disease outbreaks.
Evidence with examples
- The Great Barrier Reef has suffered repeated mass bleaching (2016, 2017, 2020, 2022, 2024); in 2024 NOAA and the ICRI confirmed the fourth global bleaching event.
- Indian reefs in the Gulf of Mannar, Gulf of Kachchh, Lakshadweep and the Andaman and Nicobar Islands have also bleached during warm-water episodes.
Cascading consequences
- Though reefs cover a tiny fraction of the ocean floor, they shelter around a quarter of all marine species; their loss threatens fisheries, coastal protection from storms, and tourism-based livelihoods.
Reversing this demands deep cuts in greenhouse-gas emissions alongside marine protected areas and reef-restoration efforts.
What an examiner expects to see
- Establish corals' narrow thermal tolerance (~23-25°C) and dependence on symbiotic zooxanthellae for nutrition and calcification.
- Explain bleaching mechanism: SST ~1°C above seasonal max for weeks makes corals expel algae, whiten and potentially die.
- Explain ocean acidification: rising CO2 lowers seawater pH and aragonite saturation, impairing skeleton-building.
- Add allied stresses: sea-level rise reducing light, intensified cyclones, and warming-linked coral diseases.
- Global example: repeated Great Barrier Reef mass bleaching and the fourth global bleaching event confirmed by NOAA/ICRI in 2024.
- Indian examples: Gulf of Mannar, Gulf of Kachchh, Lakshadweep and Andaman & Nicobar reefs.
- Impacts: reefs support ~25% of marine biodiversity; loss hits fisheries, coastal protection and tourism.
- Way forward: emission cuts, marine protected areas and reef restoration.
Concrete cases, schemes and judgments
- Great Barrier Reef mass bleaching events of 2016, 2017, 2020, 2022 and 2024
- Fourth global coral bleaching event confirmed by NOAA and ICRI in 2024
- Bleaching in India's Gulf of Mannar and Gulf of Kachchh reefs
- Lakshadweep and Andaman & Nicobar coral reefs under thermal stress
- Reefs sheltering roughly 25% of marine species despite covering under 1% of the ocean floor
Terminology to weave into the answer
coral bleachingzooxanthellaeocean acidificationsea-surface temperaturearagonite saturationmarine biodiversity