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Coral Reefs and Their Preservation

Coral Reefs and Their Preservation

What are Coral Reefs?

  • Coral reefs are the colonies of tiny living creatures that are found in oceans.
  • They are the underwater structures that are formed of coral polyps that are held together by calcium carbonate.
  • Coral reefs are also regarded as the tropical rainforest of the sea and occupy just 0.1% of the ocean’s surface but are home to 25% of marine species.
  • They are usually found in shallow areas at a depth less than 150 feet. However, some coral reefs extend even deeper, up to about 450 feet.

Types Of Coral Reefs

  • Fringing Reefs: These are coral reefs that grow in shallow waters and in areas of low rainfall runoff, primarily on the leeward side. They closely border the coastline or are separated from it by a narrow stretch of water.
  • Barrier reefs: These grow parallel to the coast, but are separated from land by a lagoon. Example: Great Barrier reef, Queensland, Australia
  • Atolls: These grow surrounding (or partly surrounding) an island which then sinks relative to sea level. Example: Maldives consists of 26 atolls.

Location Of Coral Reefs

  • Coral reefs are mainly found in tropical seas (30°N to 30°S )where the sea is shallow (less than 100m); and  warm (usually between 25° and 29°C).
  • They are also found in cold waters (temperature as low as 4°C) at depths between 40m to 2000m. Unlike tropical corals, they don’t need sunlight to survive and don’t have zooxanthellae living in their polyps. They feed solely by capturing food particles from the surrounding water. Example: They are found off the coast of Norway’s Rost Island,

Coral bleaching  | Coral Reefs and Their Preservation

  • Coral reefs are threatened by climate change.
  • When the sea surface temperature increases beyond a tolerable limit, they undergo a process of bleaching. Bleaching is when the corals expel a certain algae known as zooxanthellae, which lives in the tissues of the coral in a symbiotic relationship.
  • About 90% of the energy of the coral is provided by the zooxanthellae which are endowed with chlorophyll and other pigments.
  • They are responsible for the yellow or reddish brown colours of the host coral. The zooxanthellae can live as endosymbionts with jellyfish also.
  • When a coral bleaches, it does not die but comes pretty close to it. Some of the corals may survive the experience and recover once the sea surface temperature returns to normal levels.

Causes of Coral Bleaching | Coral Reefs and Their Preservation

  • Rise in Sea Temperature: Most coral species live in waters close to the warmest temperature they can tolerate i.e., a slight increase in ocean temperature can harm corals. El Nino elevates the sea temperature and destroys coral reefs.
  • Ocean Acidification: Due to rise in carbon dioxide levels, oceans absorb more carbon dioxide. This increases the acidity of ocean water and inhibits the corals ability to create calcareous skeletons, which is essential for their survival.
  • Solar radiation and ultraviolet radiation: Changes in tropical weather patterns result in less cloud cover and more radiations which induce coral bleaching.
  • Infectious Diseases: Penetration of bacterium like vibrio shiloi inhibits photosynthesis of zooxanthellae. These bacteria become more potent with elevated sea temperatures.
  • Chemical Pollution: Increased nutrient concentrations affect corals by promoting phytoplankton growth, which in turn supports increased numbers of organisms that compete with coral for space.
  • Increased Sedimentation: Land clearing and coastal construction result in high rates of erosion and a higher density of suspended silt particles which can
    • Smother corals when particles settle out (sedimentation),
    • Reducing light availability (turbidity) and
    • Potentially reducing coral photosynthesis and growth.
  • Human Induced Threats: Over-fishing, pollution from agricultural and industrial runoff, coral mining, development of industrial areas near coral ecosystems also adversely impact corals.

Consequences  | Coral Reefs and Their Preservation

  • Changes in coral communities can affect the species that depend on them, such as the fish and invertebrates that rely on live coral for food, shelter. Loss of such marine animals can disturb the entire food chain.
  • Declines in genetic and species diversity may occur when corals die as a result of bleaching.
  • Healthy coral reefs attract divers and other tourists. Bleached and degraded reefs can discourage tourism, which can affect the local economy.
  • Coral bleaching can cause large shifts in fish communities. This can translate into reduced catches for fishers, which in turn impacts food supply and associated economic activities.
  • Coral reefs protect coastlines by absorbing constant wave energy from the ocean, thereby protecting people living near the coast from increased storm damage, erosion and flooding.

Coral Reefs in India  | Coral Reefs and Their Preservation

  • India has its coastline extending over 7500 kilometres. It is due to the subtropical climatic conditions, there are a very few coral reefs in India. The major coral reefs in India includes the Palk Bay, the Gulf of Mannar, the Gulf of Kutch, the Andaman and Nicobar Islands and Lakshadweep Islands. Among all these coral reefs, the Lakshadweep reef is an example of atoll while the rest are all fringing reefs.
  • Palk Bay
    • Situated in the south-east coast of India, Palk Bay is separated from the Gulf of Mannar by the Mandapam Peninsula and the Rameshwaram Island and is centered on 9 °17’N and 79° 15′. The one fringing reef in the Palk Bay is 25-30 km long, and less than 200m wide lies in the east-west direction of the Pamban channel. This reef has a maximum depth of around 3 m.
  • The Gulf of Mannar
    • Situated around a chain of 21 islands, the Gulf of Mannar lies between Tuticorin and Rameswaram at a stretch of 140 km. These 21 islands fall between latitude 8°47′ N and 9° 15′ N and longitude 78° 12′ E and 79° 14’E and form a part of the Mannar Barrier Reef which is 140 km long and 25 km wide.
  • Andaman and Nicobar Islands
  • The Andaman and Nicobar Islands fall between 6°-14° N lat and 91 °-94° E longitude. They are situated at the south-eastern part of the Bay of Bengal and consist of 350 islands, of which only 38 are inhabited. These islands extend southward from the Irrawaddy Delta of Burma to the Arakan Yoma Range. All the islands of the Andaman and Nicobar groups are almost fringing reefs.
  • The Gulf of Kutch
    • The Gulf of Kutch is situated in the northern part of Saurashtra Peninsula and is located between 22°15′-23°40′ N Latitude and 68°20′-70°40′ East Longitude having an area of about 7350 sq km. These reefs are of fringing type and are about 170 km long and 75 km wide at the mouth which narrows down at a longitude of 72° 20′. Due to the mud deposits on various coral reefs, these coral reefs are in a highly degraded condition.
  • Lakshadweep Islands
    • Located between 8°N – 12°3’N latitude and 71 °E- 74°E longitude, the Lakshadweep Islands which lies scattered in the Arabian Sea are situated at about 225 km to 450 km from the Kerala Coast. The islands covering an area of 32 km2 consist of 36 tiny islands, 12 atolls, 3 reefs and 5 submerged banks, with lagoons occupying about 4200 km2.
    • Due to the warm humid climate of these islands, the temperature of the water varies between 28-31 °C with salinity ranging from 34% – 37%.

Snowflake Coral – A Threat to Biodiversity

  • Carijoa Riisei also known as snowflake coral is an invasive species discovered recently by the scientists off the coast of Thiruvananthapuram and Kanyakumari. These fast-growing species were found at a depth of 10m off Kovalam in Thiruvananthapuram and at a depth of 18m off Enayam in Kanyakumari.
  • The snowflake coral is known to cause a serious threat to the marine ecosystem due to the following reasons:
  • According to a survey conducted on Maui Black Coral Bed in 2001, it was found that the snowflake corals killed 60% of the black coral trees which was found between 80 metres to 150 metres depth.
  • They consume large quantities of the zooplanktons which can have a high ecological impact.
  • They threaten the biodiversity by displacing the native species and by monopolizing food resources.
  • It has the capacity to invade space and as a result, it can crowd out marine species like corals, algae and sponges that play a major role in maintaining the marine biodiversity.

Measures Taken For Coral Restoration By India

Reef Watch India– An NGO, has taken up two projects to conserve the reefs

  • Re(ef)Build:- It involves the restoring and rehabilitation of coral reefs at the Andamans by rescuing naturally broken coral fragments that would otherwise get smothered in the sand and die and reattaching them to a robust substratum.
  • Re(ef)Grow– The Gujarat forest department and the Zoological Survey of India are attempting to restore coral reef using the bio rock technology
  • A biostructure was installed one nautical mile off the Mithapur coast in the Gulf of Kutch
  • Bio rock means a substance formed by electro accumulation of minerals dissolved in seawater on steel structures that are lowered onto the sea- bed and are connected to a power source.
  • The technology works by sending a small amount of electrical current through electrodes in the water.
  • When negatively charged cathode and positively charged anode are placed on the seafloor, and the electric current flowing between them, calcium ions and carbonate ions combine and adhere to the structure (cathode);
  • It results in calcium carbonate formation. Coral larvae adhere to the CaCO3 and proliferate.
  • The fragments of broken corals are tied to the bio-rock structure, where they can grow faster than their actual growth as they need not spend their energy


Environment & Biodiversity

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