Threats to Coral Reefs


The Reef & Rainforest Research Centre (RRRC) has reported that some affected areas of Australia’s Great Barrier Reef are showing “substantial signs of recovery.”


  • Coral polyps are small (0.25-12 inches), soft-bodied marine organisms. They belong to the group cnidaria

Note: other cnidarians include hydras, jellyfish, and sea anemones

The coral polyps share a symbiotic relationship with algae called zooxanthellae. The zooxanthellae live inside the coral polyps and perform photosynthesis, producing food which is shared with the coral. In exchange the coral provides the algae with protection and access to light, which is necessary for photosynthesis.

Coral Reefs:

The corals secrete calcium carbonate which acts like a cement. These bind together coral, sand and pieces of rubble to form a solid structure known as the reef. The major types of coral reefs are:

  1. 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.
  2. Barrier reefs: These grow parallel to the coast, but are separated from land by a lagoon. Example: Great Barrier reef, Queensland, Australia
  3. 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 Røst Island,


In India, coral reefs are located in 7 regions:

  • Goa coast
  • Kerala coast
  • Palk Bay,
  • Gulf of Kucch
  • Gulf of Mannar
  • Lakshadweep islands
  • Andaman and Nicobar islands


Importance of coral reefs

Biodiversity: Coral reefs are extremely productive ecosystems and are called ‘the rainforests of the sea.’ Despite covering less than 0.1% of the ocean floor, reefs host more than 25% of all marine fish species and other marine animals.

Regulating services:

  • Coral reefs protect the shoreline and reduce flooding.
  • Coral reefs contribute to land accretion (opposite of land erosion)

Economic value:

  • Coral reefs support human life and livelihoods and are therefore important economically. For example: According to WWF, 1 sq.km of well-managed coral reef can yield an average of 15 tonnes of fish and other seafood annually. Further, coral reefs support tourism industry in countries like Seychelles and Maldives.

Cultural values: Coral reefs have aesthetic and recreational values

Threats to Coral Reefs:

  1. Climate Change and its impact on Coral reefs:
  • With rising global temperatures, mass coral bleaching events and infectious disease outbreaks have become more frequent.
  • Bleaching is when corals lose the highly pigmented zooxanthellae from their tissues due to stress from high sea temperatures and solar irradiation exposing the white calcium carbonate skeletons of the coral colony.

  • Ocean acidification: Carbon dioxide absorbed into the ocean from the atmosphere has been reducing calcification rates in reef-building and reef-associated organisms by changing chemical properties of seawater through a decrease in pH. This can ultimately lead to dissolving coral reefs.
  • Increased frequency and intensity of tropical storms: Violent storms will lead to coral breakage, dislocation and degradation from wind and waves
  • Changes in precipitation: increased precipitation will lead to more freshwater runoff. Freshwater run-off reduces salinity levels, may cause bleaching, and brings increased nutrients and sediments, which can lead to disease outbreak
  • Altered ocean circulation patterns may lead to lack of food due to dispersal of larvae
  1. ENSO: Sudden exposure of reef flat corals to the atmosphere during events such as extreme low tides, ENSO-related sea level drops or tectonic uplift can potentially induce bleaching. The consequent exposure to high or low temperatures, increased solar radiation and sea water dilution by heavy rains could lead to zooxanthellae loss and also cause coral death.
  2. Marine Pollution: Zooxanthellae loss occurs during exposure of coral to increased concentrations of various chemical contaminants and oil. Plastic and garbage at the seaside often ends up in the sea and disrupts the coral reefs’ delicate environment.

4. Overfishing and destructive fishing practices – such as purse seining, fine-mesh fishing, ‘moxy’ nets, cyanide fishing and blast fishing result in unsustainable damage to coral reefs

5. Coral mining (for example in south and south-east Asia) which involves blasting of reefs and coral being removed, cause immediate destruction but also result in indirect detrimental effects such as sand erosion and sedimentation

6. Sedimentation: Erosion caused by construction, mining, logging, and farming has lead to increased sediment in rivers. The sediment drastically reduces the amount of light reaching coral reefs and destroys them. Further, destruction of mangroves, which check sediments have aggravated the problem.

7. Poorly managed tourism has both direct and indirect negative effects on coral reefs. Snorkelling, diving and boating can cause direct physical damage to reefs. Overexploitation of reef species as food, for aquaria and as curios for tourist markets can threaten the survival of species.

8. Indiscriminate Exploitation of coral reefs for wildlife trade has also emerged as a major threat to coral ecosystems.

9. Massive outbreaks of predatory starfish, invasive species also pose threat to survival of corals

Extent of Coral Bleaching

  • According to a study published in the journal Science, the global proportion of coral being hit by bleaching per year has increased from 8% in the 1980s to 31% in 2016.
  • From 1980 to 2016, the number of bleaching events was highest in the western Atlantic, including Central America and the Caribbean, which experienced 3 times more events than other regions such as Australasia, the Indian Ocean and the Pacific Ocean.
  • Since 1980, 58% of severe bleaching events have been recorded during strong periods of El Nino.
  • The last coral bleaching event took place from 2014 to 2017. It had destroyed nearly 12000km of reefs. Global coral bleaching was also recorded in 1998 and 2010.
  • In 2016-17, the Great Barrier Reef of Australia suffered extreme coral bleaching which killed around 50% of its corals.

Extent and cause of coral bleaching in India:

  1. The corals of Andaman and Nicobar Islands:
  • These were severely affected by the 2004 Tsunami and have not yet fully recovered. Other reasons for coral bleaching in these islands include unregulated tourism, fishing and marine pollution
  1. Coral in the Gulf of Kachchh region:
  • Siltation and Eutrophication due to developmental activities have been the major cause of bleaching of corals.
  1. Corals of Lakshadweep islands:
  • Periodic dredging for boat passage in the lagoons, amongst others, affects the health of corals in these coral islands.
  1. Gulf of Mannar reefs
  • They are affected due to intense local activities like intensive fishing, illegal harvesting of protected species which affects the ecological balance, pollution from boats, construction along the shores etc.

Impact of Coral Bleaching:

Ecological Impacts of bleaching:

  • Decline in marine species diversity
  • Land masses will be directly exposed to waves leading to a risk of erosion.
  • Changes in coral communities affect the species that depend on them

Socioeconomic impacts of bleaching

  • Degraded coral reefs are not able to provide the ecosystem services on which local human communities depend.
  • Reefs damaged by coral bleaching can quickly lose many of the features that is important for the aesthetic appeal that is fundamental to reef tourism. Thus there is loss of revenue from tourism.
  • It can drive large shifts in fish communities. This results into reduced catches for fishers targeting reef fish species, which in turn impacts food supply and associated economic activities.
  • Coral reefs are a valuable source of pharmaceutical compounds. Degraded and dead reefs are less likely to serve as a source for important medicinal resources.

Global Initiatives

  1. International Coral Reefs Initative (ICRI)

The International Coral Reef Initiative (ICRI) is an informal partnership between Nations and organizations which aims to preserve coral reefs and related ecosystems around the world. The Initiative was founded in 1994 by eight countries: Australia, France, Japan, Jamaica, the Philippines, Sweden, the United Kingdom, and the United States of America. India is a member of ICRI

Main objectives are:

  • Encourage the adoption of best practice in sustainable management of coral reefs and associated ecosystems
  • Capacity Building
  • Raise awareness at all levels on the plight of coral reefs around the world.

The ICRI declared 2018 as the third International Year of the Reef (IYOR).

  1. Global Coral Reef monitoring network

It is a network under ICRI which works to provide scientific information and communication on the status of coral reef ecosystems to increase conservation and management for coral reefs

  1. International Coral Reef Action Network (ICRAN)

ICRAN is a strategic alliance of private and public organizations that acts worldwide to address the management of coral reef ecosystems and the needs of the communities that depend upon them. It operates by sharing and promoting traditional knowledge, current research, and best practices in order to strengthen reef management.

  1. United Nations Environment Programme (UNEP) has included coral reef conservation and restoration as an ecosystem based adaptation measure (EBA) for coastal protection.
  2. Coral Triangle Initiative: The six governments of the Coral Triangle – Indonesia, Malaysia, Papua New Guinea, the Philippines, Solomon Islands, and Timor Leste have established partnership to conserve coral reefs and the multitude of species and fisheries they support.

Conservation of Coral Reefs in India

  1. The protection of coral reef has been stressed under Wildlife Protection Act, 1972 and Environmental Protection Act, 1986 and Coastal Regulation Zone (CRZ). Corals are included in Schedule I of the Wild Life Protection Act, 1972.
  • Integrated Coastal and Marine Area Management (ICMAM) also takes up the issue of coral reef habitat destruction
  1. On the recommendations of the National Committee on Mangroves and Coral Reefs following coral reef areas in the country have been identified for intensive conservation and management since 1987:
    • Andaman & Nicobar Islands
    • Lakshdeep Islands
    • Gulf of Kutch (Gujarat)
    • Gulf of Mannar (Tamil Nadu)
  1. The coral bleaching Alert System (CBAS) has been initiated by INCOIS since 2011. This model uses the satellite derived Sea Surface Temperature (SST) in order to assess the thermal stress accumulated in the coral environs. This information yields in drawing the early signs of the intensity and spatial extents of coral bleaching
  2. Recommendations of Task Force on Islands, Coral Reefs, Mangroves and Wetlands (11th Five Year Plan 2007-2012)
  • Initiatives on conservation, development and poverty reduction in coastal areas need to be more effectively integrated
  • Development of sustainable alternative livelihoods and viable options for coastal populations to reduce the pressure on reef resources
  • Management of coral reef areas should be improved by increasing the efficiency in use of funding.
  • Increase enforcement of existing laws such as those relating to coral mining, while ensuring that populations are not deprived of livelihood options
  • Research into current conservation status of food fishes, lobsters, , sea cucumbers, ornamental fishes and other reef-associated biota
  • Appropriate regulation mechanisms to ensure that fisheries are sustainable, possibly though introduction of licenses and certification schemes.
  • Develop mechanisms for managing coral reef information, including monitoring data, and ensure that these are available to coral reef managers and decision makers.
  • Coral reef management should be seen much more ‘as a way of life’ rather than a series of short-term projects.
  • Based on the recommendations of National Committees on Wetlands, Mangroves and Coral Reefs, 24 wetland, 33 mangrove and four coral reef areas in the country have been identified by the Ministry for conservation and management
  1. National Coral Reef Research Centre has been established at Port Blair. Database Network and Website on Coral Reefs has also been established.

Steps to be taken:

  1. It is important to undertake immediate actions to address climate change under the Paris Agreement’s goal of limiting global average temperature increase to 1.5℃ above pre-industrial temperatures.
  2. Measures to combat local stressors causing coral bleaching:
  • Regulate tourism
  • Check water pollution by treating industrial effluents before discharging them into the sea, reduction is use of chemical fertilizers in farms
  • Ban fishing and harvesting of protected species.
  • Regularly service and maintain fishing vessels so that they cause minimum pollution
  • Regulate construction along the coast
  • Banning of the quarrying of massive corals.
  1. Coral restoration programs can play an important role in conserving coral reefs. For example, the innovative Force Blue project is training retired Special Forces soldiers to transplant endangered coral species
  2. A recent paper published in Nature argues that there should be focus on strengthening the reefs, to make them immune to pollution (for example through genetic engineering and of restoring reefs by targeting more resilient corals)
  3. Improved scientific knowledge is required to inform an effective response to threats to coral reefs
  4. Community awareness and education programmes are required to educate and inform the public, policymakers and other stakeholders of the ecological and socio-economic values of coral reef ecosystems
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