Coral reefs are diverse underwater ecosystems composed primarily of calcium carbonate structures secreted by corals, are built from colonies of tiny animals called coral polyps. These polyps secrete a hard exoskeleton of calcium carbonate (limestone) which forms the structural basis of the reef. These coral reefs face severe threats due to climate change, one of which is coral bleaching. Coral bleaching is a phenomenon where coral reefs lose their vibrant colors and turn completely white or pale due to the loss of symbiotic algae called zooxanthellae.

Causes of Coral Bleaching

1. Warmer Ocean Temperatures: Climate change leads to rising sea temperatures, which is a major stress factor for corals. When temperatures remain high for extended periods, corals expel the symbiotic algae (zooxanthellae) living in their tissues, causing them to turn white or “bleach.”
2. Ocean Acidification: Increased levels of carbon dioxide (CO2) in the atmosphere also contribute to ocean acidification. This makes it harder for corals to build their calcium carbonate skeletons, weakening their structure and making them more susceptible to damage from other stressors, including bleaching events.
3. Extreme Weather Events: Climate change is associated with more frequent and severe extreme weather events such as cyclones and storms. These events can physically damage coral reefs and exacerbate stress on corals, making them more vulnerable to bleaching.
4. Changes in Monsoon Patterns: In India, coral reefs are influenced by the monsoon season. Changes in monsoon patterns due to climate change, such as altered rainfall patterns or increased intensity of rainfall, can affect the water quality and temperature in coastal areas, impacting coral health.
5. Sea Level Rise: Climate change contributes to sea level rise, which can lead to increased sedimentation and coastal erosion. Sedimentation can smother coral reefs, reducing light penetration and hindering coral growth, while coastal erosion can directly damage reef structures.

Coral Reefs in India

Several coral reefs in India are under threat due to climate change and other anthropogenic factors.

1. Gulf of Mannar: Located between India and Sri Lanka, the Gulf of Mannar is home to diverse coral reefs. Climate change-induced warming and ocean acidification threaten these reefs, along with pollution from coastal development and fishing activities.
2. Andaman and Nicobar Islands: These islands in the Bay of Bengal host some of India’s most pristine coral reefs. Rising sea temperatures and severe coral bleaching events have affected reefs here, reducing coral cover and biodiversity.
3. Lakshadweep Islands: The coral reefs around the Lakshadweep Islands in the Arabian Sea face similar threats. Climate change impacts such as coral bleaching, ocean acidification, and sea level rise, compounded by local stressors like tourism and fishing, threaten the health of these reefs.
4. Palk Bay: The reefs in Palk Bay, situated between Tamil Nadu in India and Sri Lanka, are vulnerable to climate change impacts such as coral bleaching and ocean acidification. Overfishing and coastal development also contribute to their degradation.
5. Havelock Island (Andaman Islands): Havelock Island’s reefs have been significantly affected by coral bleaching events attributed to warmer sea temperatures linked to climate change.