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Coral Reefs: Types, Importance and Threats

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Coral reef is an oceanic ecosystem that is made up of corals that construct reefs. Reefs are constructed by coral polyp colonies that are connected by calcium carbonate. Most coral reefs are composed of stony corals, whose polyps cluster. Coral belongs to the animal group Cnidaria’s class Anthozoa, which includes sea anemones and jellyfish. The majority of reefs thrive in warm, shallow, clear, bright, and turbulent water. In this article, we will look into the meaning, formation, types, and importance of Coral Reefs.

What are Coral Reefs?

Coral reefs are 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 &#x2018Zooxanthellae&#x2019. 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.

Formation of Coral Reefs

The majority of coral reefs were created following the Last Glacial Period when rising sea levels from melting ice flooded continental shelves. The majority of coral reefs are under 10,000 years old. The reefs expanded higher as settlements grew, keeping pace with the sea level rise. Reefs that climbed too slowly could drown if there wasn’t enough light. Coral reefs can also be found in the deep ocean, next to oceanic islands and atolls, distant from continental shelves. Most of these islands were formed by volcanic activity. Others stem from tectonic plate movements that raised the deep ocean floor.

Types of Coral Reefs

Based on their shape, nature, and manner of occurrence, coral reefs are divided into three groups:

Coral Reefs Types and Importance

Fringing Reefs

Coral reefs that grow along the continental margins or along the Islands are known as 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 is covered with these reefs.

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. Barrier reefs are the largest and widest (in size, not distribution) of all the reefs, run hundreds of kilometers long and several kilometers 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&#x2019s largest example of a Barrier reef.

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 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.

Atolls are divided into three forms&#x2013

  • 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.

Fringing, Barrier, and Atoll Reefs

Importance of Coral Reefs

The following are some key roles that coral reefs play:

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. Economic Importance: As per an estimate, the total annual net benefit of the world&#x2019s coral reefs is around $29.8 billion. Corals are the backbone of tropical regions&#x2019 economies, through coral-related tourism and marine exports such as fisheries, etc.
  6. 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.
  7. 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.
  8. Medicinal properties: Coral reefs are called the &#x2018Medicine chests of the Oceans&#x2019. The coral skeleton, for bone grafting, is a promising lead for bone regeneration used since 1970.
  9. 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.

Coral Reefs in India

Some of the major Coral Reefs in India are:

Andaman and Nicobar Islands

Most of these islands, which are exclusively bordering reefs of roughly 572 islands in the Bay of Bengal, have a rich biodiversity.

Eastern Coast

Between the Chandrabhaga coast and Ramachandi in the Konark region of Odisha, there is a coral reef that is close to the water.

Gulf of Munnar

From Rameswaram in the north to Thoothukudi (Tuticorin) in the south, a chain of 21 islands encircles reefs. This section of the Gulf of Munnar is a protected biosphere area.

Gulf of Kutch

It consists solely of bordering reefs. The wide variety of temperatures and excessive salinity have led to the reefs’ relative underdevelopment. There is less biodiversity in the harbors. Additionally referred to as a marine national park, the entire Gulf of Kutch.

Lakshadweep

36 islands, all coral atolls, with 10 of them being inhabited. The islands’ lengths range from less than 1 km to around 9 km, and their maximum breadth is 2 km.

Western Coast

Inlets in the western portion of the Gulf of Khambat have a few coral reefs surrounding them. A coral reef called Angria Bank is located near Vijaydurg, Maharashtra. Malwan, Maharashtra’s Tarkarli is a tiny reef. Karnataka’s Netrani Island has a coral reef.

Threats to Coral Reefs

The following is a list of the threats affecting coral reefs:

  1. Overexploitation for food, aquarium commerce, souvenir trade, and medical uses.
  2. Destructive fishing methods that cause irreparable harm, such as blast fishing, purse seining, fine-mesh fishing, “Moxy” nets, and cyanide fishing, frequently go hand in hand with overfishing. Coral reefs are harmed by “Moxy” nets, fine-mesh nets, and bottom trawlers.
  3. Coral reefs in the vicinity are also suffering from marine pollution brought on by ship trash, ship ballast water discharge, and oil, which frequently leaks into the oceans.
  4. Coral reefs are negatively impacted by poorly managed tourism in both direct and indirect ways. Direct physical damage to reefs can result from snorkeling, diving, and boating, and overharvesting reef species for human consumption, aquarium use, and tourist markets poses a threat to their continued existence.
  5. Coral reefs are already in danger, and the threat from climate change and global warming is increasing.
  6. Ocean acidification, coral bleaching, sea level rise, rising ocean temperatures, and increased dissolved carbon dioxide all pose threats to coral reefs.

FAQs on Coral Reefs

1. What makes coral reefs so important?

Answer:

Coral reefs offer possibilities for recreation, serve as a barrier against erosion and storm damage, and support local economies. They are also a source of fresh medications and food. More than 500 million people rely on reefs for safety, income, and food.

2. What defines a Coral Reef?

Answer:

Coral reefs are the massive seawater structures formed by the accumulation of tiny-bodied organisms known as coral.

3. Where are Coral Reefs found in India?

Answer:

The Gulf of Mannar, the Gulf of Kutch, the Andaman and Nicobar Islands, and the Lakshadweep Islands are the only places in India with significant reef formations. The other reefs are all fringing reefs, whereas the Lakshadweep reefs are atolls. The country’s central west coast has patchy coral in the intertidal zones.

4. What are the three main types of coral reefs?

Answer:

The three main types of coral reefs are Fringing, Barrier, and Atoll.



Last Updated : 16 Aug, 2023
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