Coral Ecosystem


  • Coral reefs are some of the most diverse ecosystems in the world.
  • Coral polyps, the animals primarily responsible for building reefs, can take many forms: large reef building colonies, graceful flowing fans, and even small, solitary organisms.
  • Thousands of species of corals have been discovered; some live in warm, shallow, tropical seas and others in the cold, dark depths of the ocean.

Each individual coral is referred to as a polyp. Coral polyps live on the calcium carbonate exoskeletons of their ancestors, adding their own exoskeleton to the existing coral structure. As the centuries pass, the coral reef gradually grows, one tiny exoskeleton at a time, until they become massive features of the marine environment.

Corals are found all over the world’s oceans, from the Aleutian Islands off the coast of Alaska to the warm tropical waters of the Caribbean Sea. The biggest coral reefs are found in the clear, shallow waters of the tropics and subtropics. The largest of these coral reef systems, the Great Barrier Reef in Australia, is more than 1,500 miles long (2,400 kilometers).


  • Shallow water, reef-building corals have a symbiotic relationship with photosynthetic algae called zooxanthellae, which live in their tissues.

( The coral provides a protected environment and the compounds zooxanthellae need for photosynthesis. In return, the algae produce carbohydrates that the coral uses for food, as well as oxygen. The algae also help the coral remove waste. Since both partners benefit from association, this type of symbiosis is called mutualism.

Deep-sea corals live in much deeper or colder oceanic waters and lack zooxanthellae. Unlike their shallow water relatives, which rely heavily on photosynthesis to produce food, deep sea corals take in plankton and organic matter for much of their energy needs.)

  • Stable climatic conditions: Corals are highly susceptible to quick changes. They grow in regions where climate is significantly stable for a long period of time.
  • Perpetually warm waters: Corals thrive in tropical waters [30°N and 30°S latitudes, The temperature of water is around 20°C] where diurnal and annual temperature ranges are very narrow.
  • Clear salt water: Clear salt water is suitable for coral growth, while both fresh water and highly saline water are harmful.
  • Abundant Plankton: Adequate supply of oxygen and microscopic marine food, called plankton [phytoplankton], is essential for growth. As the plankton is more abundant on the seaward side, corals grow rapidly on the seaward side.
  • Little or no pollution: Corals are highly fragile and are vulnerable to climate change and pollution and even a minute increase in marine pollution can be catastrophic.

Coral reefs take few principal forms like.

(1) Fringing reefs consist of flat reef areas that directly skirt a nonreef island, often volcanic, or a mainland mass.

(2) Barrier reefs are also close to a non reef landmass but lie several kilometres offshore, separated from the landmass by a lagoon or channel often about 50 metres (160 feet) deep. Some barrier reefs are more or less circular, surrounding an island, but larger barrier reefs, such as those along the Red Sea coast and Australia’s Great Barrier Reef, are complex linear features consisting of chains of reef patches, some of them elongated into ribbon reefs.

(3) Atolls are like circular barrier reefs but without their central landmass.

  • Coral reefs protect coastlines from storms and erosion, provide jobs for local communities, and offer opportunities for recreation.
  • They are also are a source of food and new medicines.
  • Over half a billion people depend on reefs for food, income, and protection.
  • Fishing, diving, and snorkeling on and near reefs add hundreds of millions of dollars to local businesses.
  • The net economic value of the world’s coral reefs is estimated to be nearly tens of billions of U.S. dollars per year.
  • These ecosystems are culturally important to indigenous people around the world.

  • Unfortunately, coral reef ecosystems are severely threatened.
  • Some threats are natural, such as diseases, predators, and storms.
  • Other threats are caused by people, including pollution, sedimentation, unsustainable fishing practices, and climate change, which is raising ocean temperatures and causing ocean acidification.
  • Many of these threats can stress corals, leading to coral bleaching and possible death, while others cause physical damage to these delicate ecosystems.
  • During the 2014-2017 coral bleaching event, unusually warm waters (partially associated with a strong El Niño) affected 70% of coral reef ecosystems worldwide.
  • Some areas were hit particularly hard, like the Great Barrier Reef in Australia, where hundreds of miles of coral were bleached.

Corals are able to recover from bleaching events if conditions improve before they die, though it can take many years for the ecosystems to fully heal. Scientists are also testing new ways to help coral reef ecosystems, such as growing coral in a nursery and then transplanting it to damaged areas.


Coral reef threats in India

  • Recent studies by the National Institute of Oceanography have shown that Reckless tourism is damaging Malvan’s coral reefs.
  • Similar injuries to Goa’s coral reefs are likely due to scuba diving and snorkeling and similar activities.
  • The prevalence of coral physical damage in the Marine Protected Area has increased from 4.83% in 2016 to 11.58% in 2019 with cumulated physical damage of 33.08% in the last four years.
  • The Gulf of Munnar corals usually bleach in summer if water temperature surpassed 30 degrees Celsius.
  • A coral bleaching alert report protocol developed by Spece Application Center (SAC), Ahmedabad recorded that the years 1998, 2010, and 2016 witnessed mass bleaching in the five coral reefs.
  • They observed that Andaman, Nicobar, and Gulf of Kutch regions recorded threat in 2010, while the Gulf of Mannar recorded threat in 2016.
  • According to the International Union for Conservation of Nature (IUCN), India’s coastal and marine ecosystem along with coral reefs is under increasing threat due to overexploitation of resources.

What are the government actions to protect Coral reefs?

  • The government of India seeks to protect, sustain, augment coral reefs in the country by both regulatory and promotional measures.
  • Under Coastal Regulation zone notification, and Island Protection Zone notification, corals are sought to be protected by regulating developmental activities along the sea coast.
  • The laws that have a bearing on coral reef areas are the Indian Forest Act, 1927, the Forest Conservation Act, 1980, and the Indian Fisheries Act.
  • Integrated Coastal and Marine Area Management launched in 1998 aims at integrating the management of coastal and Marine areas has prepared model plans for the Gulf of Kutch.
  • India has also created mechanisms such as the National Coastal Zone Management Authority (NCZMA) and State Coastal Zone Management Authority for the protection of coastal and marine areas.
  • Ministry of Environment and Forests (MoEF), India has included studies on coral reef under the Coastal Zone Studies (CZS).
  • Despite such efforts, a dedicated coral protection program is lacking in India and this is affecting the coral protection programs conducted by concerned state governments.


Where are Coral reefs located in India?

  • India with its coastline of 7,517 km and subtropical climatic conditions has coral reef areas along its coastline and islands.
  • All the three major reef types, atoll, fringing, and barrier, occur in India.
  • In India, Coral reefs are present in the areas of Gulf of Kutch, Gulf of Mannar, Andaman & Nicobar, Lakshadweep Islands, and Malva

  • The Gulf of Kutch in the northwest, which has some of the most northerly reefs in the world) and Palk Bay and the Gulf of Mannar in the southeast.
  • Coral patches are found in Ratnagiri, Malvan, and Redi, south of Bombay and at the Gaveshani Bank, west of Mangalore.
  • Corals along the shore are found at Quilon on the Kerala coast to Enayem in Tamilnadu.
  • Corals also occur on the east coast between Parangipettai (Porto Novo), south of Cuddalore, and Pondicherry.
  • Among island corals, in Andaman and Nicobar Islands (Fringing and barrier) and Lakshadweep (Atolls) corals are found.


  • Coral bleaching occurs when coral polyps expel algae that live inside their tissues. Normally, coral polyps live in an endosymbiotic relationship with these algae, which are crucial for the health of the coral and the reef.
  • The algae provides up to 90 percent of the coral’s energy. Bleached corals continue to live but begin to starve after bleaching.
  • The leading cause of coral bleaching is rising water temperatures.
  • A temperature about 1 °C (or 2 °F) above average can cause bleaching.
  • According to the United Nations Environment Programme, between 2014 and 2016 the longest recorded global bleaching events killed coral on an unprecedented scale.
  • In 2016, bleaching of coral on the Great Barrier Reef killed between 29 and 50 percent of the reef’s coral.
  • In 2017, the bleaching extended into the central region of the reef.
  • The average interval between bleaching events has halved between 1980 and 2016.


Factors responsible for Coral Bleaching

  • Increased water temperature (most commonly due to global warming), or reduced water temperatures
  • Oxygen starvation caused by an increase in zooplankton levels
  • Increased solar irradiance (photosynthetic active radiation and ultraviolet light)
  • Increased sedimentation (due to silt runoff)
  • Bacterial infections
  • Changes in salinity
  • Herbicides
  • Extreme low tide and exposure
  • Cyanide fishing
  • Pollutants such as oxybenzone, butylparaben, octyl methoxycinnamate, or enzacamene: four common sunscreen ingredients that are nonbiodegradable and can wash off of skin
  • Ocean acidification due to elevated levels of CO2 caused by air pollution
  • Being exposed to Oil or other chemical spills



The future of the Great Barrier Reef

The largest coral reef in the world, the Great Barrier Reef, is home to at least 400 individual species of coral and thousands of different species of fish, mollusks, sea snakes, sea turtles, whales, dolphins, birds and more. As with the other coral reefs of the world, this incredible ecological hotspot is under threat.

A heat wave in 2016 caused a large percentage of the corals in the Great Barrier Reef to undergo severe bleaching and death. A 2018 study in the journal Nature Communications found that in just the northern third of the reef, over 60 percent of the shallow-water corals (those below 49 feet, or 15 meters) experienced some degree of bleaching, and 30 percent of the coral died. The study also found that even in the deeper, less-explored areas of the reef (down to about 131 feet or 40 m), nearly 40 percent of the corals had at least partial bleaching.

Healthy reefs lead to healthy oceans, and healthy oceans are vital to all life on Earth. The destruction facing not only the Great Barrier Reef, but also every reef around the world, can lead to the extinction of thousands of species of marine life. In turn, coastlines currently protected by reefs would more readily flood during storms, some islands and low-lying countries would vanish under the water, and the $30 billion industry that coral reefs provide could collapse.



1) What is the importance of coral reefs to the global environment and economy? Discuss in what way loss of corals can cause damage not only to climate but also to social, cultural and economic activities. (250 words)


2)What causes coral bleaching at the Great Barrier Reef?


3)Evaluate the impact of global warming on the coral life system of the world with examples. (250 words)


4)Discuss therising threat and impact of coral bleaching on coral reefs of the World. (250 words)


5) ”Rising Climate change guarantees coral reef extinction in coming 100 years”. Discuss(250 words)