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Coral Reefs: Types and Importance

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  • Last Updated : 25 Mar, 2022
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Coral reefs are the massive seawater structures formed by the accumulation of tiny-bodied organisms known as coral. Corals are living animals that have a symbiotic relationship with microscopic algae called ‘Zooxanthellae’. Each coral is referred to as a Polyp and each polyp secretes lime, whose agglomeration results in the formation of coral reefs over a period of time. Coral reefs are of three types i.e. fringing, barrier, and atoll reefs, and each reef has a difference in its formation and distribution. Coral reefs are much more than just a beautiful oceanic ecosystem, they provide an important support system to underwater life, protect coastal areas, and provide a source of income for millions of people along with food and medicine.

Types of Coral Reefs:

A. Fringing Reefs (also named as Shore Reefs)

  • Coral reefs grow along the continental margins or along the Islands fringing reefs.
  • Fringing reefs are reefs that develop directly from the shore. They are located very near to land.
  • A fringing reef runs as a narrow belt of around 1-2 km wide. The seaward slope is steep, shallow, and narrow while the landward slope is gentle. Therefore,  these coral reefs are generally long but narrow in width.
  • Fringing reefs are generally attached to the coastal land but sometimes there is a gap between fringing reefs and the mainland which forms a Lagoon and such lagoons are known as ‘Boat channels‘.
  • Coral polyps do not extend outwards of these reefs due to sudden and large increases in-depth as they lack food there.
  • The fringing reefs are the most commonly found reefs across the world in all major types of reefs.
  • In India, the Gulf of Kachchh, the Gulf of Mannar, the coastline of Andaman and Nicobar Islands are covered with these reefs.

Coral Reefs Types and Importance

B. Barrier Reefs:

  • Barrier reefs are extensive, highest, and widest linear reefs which run parallel to a shore and are separated by a lagoon many times.
  • These lagoons are extensive but shallow between the coastal land and the barrier reef.
  • Barrier reefs are the largest and widest (in size, not distribution) of all the reefs, run hundreds of kilometres long and several kilometres wide.
  • These reefs are rarely found as a continuous chain; they are broken at many places and have contact with open seas and oceans through the tidal inlets.
  • These reefs usually run parallel to the coastline for some distance.
  • Barrier reefs are far less common than other types of reefs, mainly found in the tropical Atlantic as well as the Pacific.
  • The 1200 mile long Great Barrier Reef Located parallel to the east coast of Australia is the world’s largest example of a Barrier reef.
  • The reef is broken at many places and there are frequent openings in form of tidal inlets which enable the logon to maintain contact with open seas.

C. Atolls:

  • An atoll is a ring of narrow growing coral reef systems which surround a large and deep central lagoon.
  • The corals are generally found around an Island or an elliptical form of submarine platform.
  • The lagoon has a depth of 80 to150 meters and is usually joined with seawater through a number of channels cut across the reef.
  • Atolls are generally located far away from coastal land because the submarine features help in the development of atolls. Such as a submerged island and volcanic cone provide suitable conditions for coral growth.
  • Atolls are generally formed on mid-oceanic ridges as they provide prerequisites for the formation of Atolls.
  • Atolls are divided into three forms
  • True atoll: A circular reef enclosing a lagoon without island;
  • Island atoll: Having an island in the central part of the lagoon and enclosed by circular Reef
  • Coral island or an Atoll island: It is an atoll reef, built by the process of erosion and deposition of marine waves, as it does not have an island in the beginning.
  • Atolls are more common in the Pacific ocean than in any other ocean. The Fiji atoll, the Funafuti atoll in the Ellice Island, atolls of Cook island are a few examples.
  • The Indian Ocean also contains numerous atoll formations. Such as found in the Maldives and Chagos island groups, Lakshadweep Islands, Seychelles, and in the Cocos Island group.

Fringing, Barrier, and Atoll Reefs

Significance of Coral Reefs:

A. Coastal Protection: Coral reefs act as a barrier and protector of coastal areas from strong oceanic currents, waves, oceanic storms, cyclones, and Tsunamis. With more frequent storms and cyclones due to climate change, coral reefs become more important. Some coastlines, in the 2004 Tsunami, were protected from severe damage because of healthy coral reefs.

B. Basis of Other Ecosystems: For the formation of mangroves and other coastal forests, the grazing of corals by parrotfish leads to the formation of large expanses of sand; and with the action of oceanic currents, it leads to the formation of islands and shallows over the sand formed by corals, where another ecosystem emerges over time.

C. Food Source: Fish that live in and around coral reefs are a source of protein for billions of people across the world, mainly living on coastlines. Some fishing industries are totally dependent on it. Around 10% of the fish caught worldwide and 70-90% for Southeast Asian countries depend on corals.

D. Meteorology: A study by the Indian Institute of Tropical Meteorology (IITM) stated that corals along the north-western coast provide insights regarding the patterns of the onset and withdrawal of Indian monsoons.

E. Economic Importance: As per an estimate, the total annual net benefit of the world’s coral reefs is around $29.8 billion. Corals are the backbone of tropical regions’ economies, through coral-related tourism and marine exports such as fisheries, etc.

F. Tourism: The GDP of many countries with coral reef industries comes from the tourism sector as it generates billions and provides jobs for millions around the world.

G. Maintenance of Biodiversity: Thousands of species can be living on one coral reef. Coral Triangle, a coral-rich marine region in Southeast Asia that encompasses the waters between Indonesia, the Philippines, and Papua New Guinea, is the most biodiverse marine ecosystem on Earth.  

H. Medicinal properties: Coral reefs are called the “Medicine chests of the oceans’. The coral skeleton, for bone grafting, is a promising lead for bone regeneration used since 1970.

I. Carbon Sequestration: Coral reefs are an important reservoir of carbon and help in the sequestration of ocean carbon, hence an important part of the carbon cycle.

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