Coral reefs of India

Prelims and MainsCurrent affairs on this: Marine and coastal ecosystems

A coral reef is built by animals: polyps, relatives of jellyfish, that secrete calcium carbonate skeletons and host single celled algae, zooxanthellae, in their tissue. The algae photosynthesise and feed the polyp, which is why reef building corals need warm, clear, shallow, salty water with sunlight, and why reefs sit in the tropics between about 30°N and 30°S. India has four major reef regions: the Gulf of Kachchh, the Gulf of Mannar, Lakshadweep and the Andaman and Nicobar Islands, with smaller patches at Malvan, Netrani and Angria Bank. Bleaching is what happens when the water stays too warm: the polyp expels its algae, turns white, and starves unless the water cools within weeks. Warming seas have made mass bleaching recurrent; the fourth global bleaching event, declared in 2024, reached Lakshadweep and the Gulf of Mannar. Reefs shelter a quarter of marine species, protect coasts from waves and support fisheries.

• Hard corals build reefs (hermatypic); soft corals do not, having no rigid skeleton. Reef types: fringing (along a shore, Andaman), barrier (separated by a lagoon), atoll (a ring around a sunken island, Lakshadweep) and patch reefs.
• Bleaching is a heat stress response, measured in degree heating weeks; a reef that bleaches can recover if the heat passes, but repeated bleaching kills it. Ocean acidification, from dissolved carbon dioxide, separately slows skeleton building.
• India's protection: the Gulf of Mannar Marine National Park (1986) and Biosphere Reserve (1989), Gulf of Kachchh Marine National Park (1982), and the Coastal Regulation Zone rules, which bar construction and dredging on reef coasts.
• Restoration methods in the news: coral gardening and transplanting on frames, and mineral accretion (Biorock), where a low current speeds carbonate deposition; Gulf of Kachchh and Lakshadweep trials.
• Other threats: sedimentation from coastal works, crown of thorns starfish outbreaks, destructive fishing, tourism damage; the 2004 tsunami uplift in the Andamans killed reefs by exposure.

Mains: Coral bleaching is the clearest sign that ocean warming has already crossed an ecological threshold, and India's reefs, all within two degrees of their thermal limit, are where the effect will show first on a coast that depends on them for fish and storm protection.

Further reading: Coral reefs and climate change (IUCN)

See also: MISHTI · India's mangroves: what they are worth and what they lose · Marine fish stock accounts · National report on deep-sea fishery resources