Mains Practice Question


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Why coral reefs in India are undergoing severe bleaching?


A Simple Introduction about Coral Reefs

Coral reefs are among the most biologically diverse marine ecosystems on Earth, with a history spanning approximately 200 million years. These reefs are vital components of the marine ecosystem, providing essential habitats for a wide array of marine vegetation and wildlife.

Ecologically, coral reefs are comparable to tropical rainforests in terms of species richness and biological productivity. They play a crucial role in promoting the establishment of related ecosystems, which support important habitats, fisheries, and livelihoods. Thus, the health and preservation of coral reefs are critical for maintaining marine biodiversity and supporting human communities that rely on these ecosystems.



You may incorporate some of the following points in the body of your answer:

Coral Bleaching and Its Impact

Causes of Coral Bleaching

Coral bleaching occurs when water temperatures become excessively warm, causing corals to expel the microscopic algae living in their tissues. These algae are crucial for the corals as they provide nourishment through photosynthesis. Without these algae, the corals' tissues become transparent, revealing their white skeletons, a phenomenon known as coral bleaching.

Effects and Risks of Bleaching

Bleached corals are not dead but are at significant risk of malnutrition and disease. Scientists estimate that corals can survive without their algae for around two weeks. Thermal stress, which causes bleaching, occurs when sea surface temperatures exceed 1 degree Celsius above the maximum mean temperature, and this stress intensifies if high temperatures persist.

Measuring Heat Stress

Scientists use the Degree Heating Week (DHW) indicator to measure accumulated heat stress in a given area over the previous 12 weeks. This indicator sums up any temperatures that surpass the bleaching threshold during that period, expressed in Celsius weeks.

Regional Impacts and Case Studies

The western Indian Ocean region has experienced the most significant increase in marine heatwaves, with approximately 1.5 events per decade, followed by the north Bay of Bengal at 0.5 events per decade. An underwater assessment showed that 85% of the corals in the Gulf of Mannar near the Tamil Nadu coast bleached after the marine heatwave in May 2020.


The ending of the answer should be on a positive note and it should have a forward-looking approach.

Coral reefs, vital components of marine ecosystems, are home to diverse marine life and play a crucial role in supporting the overall health and biodiversity of the oceans. Protecting these vulnerable ecosystems is essential for preserving marine biodiversity and sustaining the livelihoods of coastal communities.


Other Points to Consider 

Heat waves

Importance of corals


Previous Year Questions

1. Describe the key points of the revised Global Air Quality Guidelines (AQGs) recently released by the World Health Organisation (WHO). How are these different from its last update in 2005? What changes in India’s National Clean Air Programme are required to achieve revised standards? (2021)
2. Explain the causes and effects of coastal erosion in India. What are the available coastal management techniques for combating the hazard? (2022)


21-May 2024