Introduction to Coral

An individual coral is known as a “polyp”. They are living animals that secrete calcium carbonate to form hard skeletal structures called reefs. Coral lives a symbiotic relationship with a unicellular microscopic alga called zooxanthellae. Coral get their colors from these algae. Algae give off oxygen and other nutrients that the coral polyps need to live, and in return, the polyp gives the algae shelter, carbon-dioxide & other substances.

They are known as ‘tropical rainforest of oceans’ due to huge productivity and have the highest biodiversity among all the marine ecosystems.

Ideal Conditions for coral formations

  • Water temperature not less than 20 Deg. Celsius (Thus, found mainly in tropical and sub-tropical waters.)
  • Not usually found on west coasts of continent, due to presence of cold currents.
  • Found at depth of no more than 100-180 feet (as sunlight does not reach below this depth).
  • However, few deep-sea corals are found at depth beyond 2000 meters that tolerate very cold temperatures and do not depend on sunlight (thus, do not contain zooxanthellae). For e.g. In Norway, Canada, Antarctica etc.
  • Coral survive in water that is free moving, saltish, and free from sediments (allow a free supply of food & oxygen)


  • Bleaching or paling of coral occurs when-
  • Coral polyps expel algal cells (zooxanthellae), thus losing their color to become white.
  • There is a decline in the concentration of photosynthetic pigments in zooxanthellae.
  • Normally corals can re-establish themselves (or return to their pre-bleaching state) in a decade or two. But the quick frequency and intensity of MCBs- (marine cloud brightening) overwhelm coral reef’s ability to recover from heat stress episodes.
  • Over-extended periods of coral bleaching can result in the coral’s death.
Marine Cloud Brightening

It has the potential to lower sea surface temperatures in targeted areas, potentially reducing the frequency and severity of coral bleaching events. This could provide a lifeline for corals, enabling their survival and recovery as well as the way to safeguard marine ecosystems.


  • Global warming i.e. rising ocean temperature.
  • It can’t survive in very high/low temperatures.
  • Diseases g. white band Disease, Coral Plague, Black Band Disease
  • Marine pollution g. ocean acidification, changing salinity, oil leakage, ocean sedimentation etc.
  • Climatic causes g. Tropical cyclones, monsoon winds, Frequent formation of El Nino etc.
  • Oxygen Starvation- due to eutrophication or increase in zooplanktons due to overfishing etc.


  • Fringing reefs
  • They grow near coastline around islands/continents and extend seawards (splashing waves that bring in nutrients & oxygen).
  • Separated from shore by narrow, shallow lagoons.
  • Fringing reefs are most common type of reef.


  • Barrier reefs
  • They are also parallel to the coastline but are separated from the mainland by deeper, wider lagoons. They are partially submerged.
  • At their shallowest point, they can reach the water’s surface forming a “barrier” to navigation.
  • The Great Barrier Reef in Australia is the largest and most famous barrier reef in the world.


  • Atolls
  • They are rings of coral that create protected lagoons & are located in the middle of the sea.
  • Atolls usually form when islands/land surrounded by fringing reefs sinks into sea or sea levels rises around them (these islands are often the tops of underwater volcanoes).
  • Fringing reefs continue to grow and eventually form circles with lagoons inside. E.g. Atolls in the Maldives.


  • Protect shorelines from big waves by absorbing wave energy.
  • Nutrient recycling and Nitrogen fixation, thereby supporting marine ecosystem.
  • Provide a safe place for fish to spawn (release eggs into the water)
  • Provide habitats for a large variety of organisms.
  • Provide food (fish) and livelihoods.
  • Help in the carbon cycle. They convert carbon-dioxide in ocean to limestone, thus enabling carbon sequestration.
  • Aiding development of many anti-cancer drugs and painkillers.


India’s has four major reef areas

  1. Gulf of Mannar (Fringing Reef)
  2. Gulf of Kachchh (Barrier Reef)
  3. Lakshadweep (Atoll)
  4. Andaman and Nicobar Islands (Fringing Reef)


  • Gulf of Mannar biosphere reserve
  • Gulf of Kutch Marine national park
  • Mahatma Gandhi Marine National Park, Andaman and Nicobar
  • Lakshadweep
  • Rani Jhansi Marine National Park in Richie’s Archipelago, south Andaman Islands.
  • Coral Bleaching Alert System (CBAS)- a service initiated from INCOIS (Indian National Center for ocean information services that uses the satellite-derived Sea Surface Temperature (SST) to access thermal stress accumulated in the coral environments.
  • Regulatory Provisions-
  • Coastal regulation Zone (CRZ) Notification and Island protection zone (IPZ) Notification derived under Environment protection act, 1986, to regulate the developmental activities along the sea coast and tidally influenced water bodies.
  • Mangroves & Coral Reefs are categorized as ecological sensitive areas (CRZ-I) where no new constructions are permitted.
  • Coral Reef is included in Schedule I of the Wildlife protection act, 1972 which affords it the highest degree of protection.
  • Protected areas- National Parks, Sanctuaries & Marine Biosphere Reserve have been created under the provisions of the wild life (protection) Act, 1972 to conserve marine life including coral reefs.
  • Enforcement: The Wildlife Crime Control Bureau has also been set up to strengthen the enforcement of the law for the control of poaching and illegal trade in wildlife and its products.
  • Schemes- centrally sponsored scheme on conservation of management of mangroves and coral Reefs- 100% Central Assistance to the Coastal states/UTs.
  • Global Coral Reef research and development (R&D) Accelerator Platform-
  • Objective- to create a global R&D program to advance research, innovation and capacity building in all facets of coral reef conservation, restoration, and adaptation.
  • Finance- it will be funded by voluntary contributions by G20 members, non-member countries and private sector actors.

International Coral Reef Initiative (ICRI)

  • Founded in 1994 by 8 governments: Australia, France, Japan, Jamaica, Philippines, Sweden, the United Kingdom, the United States of America.
  • Announced at the 1st conference of the parties of the convention on Biological Diversity in 1994.
  • Decisions not binding on members.
  • Members- more than 60 members including India
  • Objective- to encourage the adoption of best practice in sustainable management of coral reefs and associated ecosystems, build capacity, & raise awareness at all levels.

Source- Wikipedia, PIB, TH