What are Corals?


Corals Structure

  • Corals are related to sea anemones, and they all share the same simple structure, the polyp.
  • The polyp is open at just one end and the other end has a mouth surrounded by a ring of tentacles. The tentacles have stinging cells, called nematocysts, that allow the coral polyp to capture small organisms that swim too close. Inside the body of the polyp are digestive and reproductive tissues.
  • Corals and Zooxanthellae show mutualism. Zooxanthellae (are single-celled algae) photosynthesize and pass some of the food they make from the sun’s energy to their hosts, and in exchange, the coral animal gives nutrients to the algae.
  • The green, brown, and reddish colour of the corals are because of zooxanthellae.
  • Rare colours of purple, blue, and mauve are made by corals themselves.

Climatic Conditions required for their survival

  • Shallow and clear water, where sunlight is available.
  • Warm waters (temperature should be between 20°C to 32°C).
  • Marine waters (balance of salt and water).


  • Diversity of corals is highest amongst all the marine ecosystems (1/4th of all oceanic species are dependent on coral reefs for food and shelter). This is the reason they are also called rainforest of oceans.
  • It provides food, shelter, tourism jobs and medicines to humans. Their value is estimated at 30 billion US Dollars.
  • They consume particulate matter suspended in the ocean waters. This contributes to enhanced quality and clarity of our nearshore waters.

Coral Reefs

  • Hard corals extract calcium carbonate from seawater to create a hard, durable exoskeleton that protects their soft, sac-like bodies. These are also called hermatypic corals.
  • Coral reefs are formed from the skeletons of these hard corals.
  • The coral reef gradually grows, one tiny exoskeleton at a time, until they become massive features of the marine environment.
  • World’s largest coral reef is “The Great Barrier Reef” in Australia.
  • There are Three types of Coral reefs.

Barrier Reef: these are parallel to the coast, separated by lagoons.

Fringing Reef: these grow near coastlines near islands and continents.

Atolls: these are rings of coral that create protected lagoons and are usually located in the middle of the sea.

Corals reefs in India

  • Andaman and Nicobar Islands (fringing reefs in the Bay of Bengal)
  • Gulf of Mannar (fringing reefs in the Indian Ocean)
  • Gulf of Kutch (fringing reefs in the Arabian Sea)
  • Lakshadweep Islands (coral atolls in the Arabian Sea)

Related sources: Biodiversity Hotspots, Optics: Visible, infrared and ultraviolet

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  1. […] Related sources: What are Biodiversity Hotspots and their Prominent Locations in India?, What are Corals? […]

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