Coral Reef

Coral Reef for UPSC IAS
  • A coral reef is an underwater ecosystem characterized by reef-building corals.
  • Reefs are formed of colonies of coral polyps held together by calcium carbonate.
  • Most coral reefs are built from stony corals, whose polyps cluster in groups.

What are the types of Coral Reefs?

Coral Reefs are differentiated into three categories based on their shape, nature and mode of occurrence.

  1. Fringing Reef:
    1. The coral reefs that are found very close to the land and form a shallow lagoon known as Boat Channel are called Fringing Coral Reefs.
    2. The Fringing Reefs develop along the islands and the continental margins.
    3. They grow from the deep bottom of the sea and have their seaward side sloping steeply into the deep sea.
    4. Fringing Reefs are the most commonly found coral reefs among the three.
    5. For example Sakau Island in New Hebrides, South Florida Reef.
  2. Barrier Reef:
    1. Barrier Reefs are considered the largest, highest and widest reefs among the three coral reefs.
    2. They develop off the coast and parallel to the shore as a broken and irregular ring.
    3. Being the largest reef among all, they run for 100 km and are several kilometres wide.
    4. One example of a Barrier Reef is the Great Barrier Reef of Australia which is 1200 miles long.
  3. Atolls:
    1. An atoll can be defined as a reef that is roughly circular and surrounds a large central lagoon.
    2. This lagoon is mostly deep having a depth of 80-150 metres.
    3. The atolls are situated away from the deep sea platforms and are found around an island or on a submarine platform in an elliptical form.
    4. For example Fiji Atolls, Suvadivo in Maldives and Funafoothis Atoll of Ellice.

What are the Factors that affect Coral Reefs?

  • Extreme climate conditions:
    • The high temperature of water leads to the decline of these corals as they cannot survive in high temperatures.
    • As estimated by scientists, most of the coral reefs of the world will soon decline with the increasing rates of ocean warming.
  • Overfishing:
    • It is another major concern as it is leading to an ecological imbalance of the coral reefs.
  • Coastal development:
    • The development of coastal infrastructure and tourist resorts on or close to these coral reefs causes significant damage.
  • Pollution:
    • The toxic pollutants which are dumped directly into the ocean can lead to the poisoning of the coral reefs as it increases the nitrogen level of the seawater leading to an overgrowth of algae.
  • Sedimentation:
    • Construction along the coasts and islands leads to soil erosion increasing the sediments in the river.
    • As a result, it can smother corals by depriving them of the light needed to survive.

Coral Reefs in India

  • India has a coastline extending over 7500 kilometres.
  • There are very few coral reefs in India due to the subtropical climatic conditions.
  • The major coral reefs in India include the Palk Bay, the Gulf of Mannar, the Gulf of Kutch, the Andaman and Nicobar Islands and the Lakshadweep Islands.
  • Among all these coral reefs, the Lakshadweep reef is an example of an atoll while the rest are all fringing reefs.

Latest News

  • 20 April 2023:
    • Recently, a scientific expedition has discovered a previously unknown coral reef with abundant marine life off Ecuador’s Galapagos Islands.


  1. The Hindu

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