The Importance of Coral Reefs and Related Threats

This article on The Importance of Coral Reefs…

Presented by Aakriti Yadav-

According to the Intergovernmental Panel on Climate Change (IPCC), Sixth Assessment report on ‘Impacts, Adaptation, and Vulnerability’ 2022, the degradation and loss of coral reefs can affect about 4.5 million people in Southeast Asia the Indian Ocean.

About Coral Polyps

Coral reefs are significant submarine features. These are formed due to the accumulation of skeletons of lime secreting organisms known as coral polyps. These bind together corals to form a solid structure known as Reefs.

Coral Polyps are small ( 0.25-12 inches), soft-bodied marine organisms. They belong to the group of Cnidaria. Coral polyps share a symbiotic relationship with algae called Zooxanthellae. Zooxanthellae algae are the photosynthetic unicellular plant alga, of different colors and embedded in the tissues of the outer bodies of Coral polyps called Coral symbiotic partners.  They provide the food requirements of living corals and recycle the excreta and wastes out of corals, in turn, coral organisms provide them some shelter in their bodies. Thus they are mutually dependent on each other.

Conditions for the growth of Coral polyps

1. Corals grow in open seas and oceans. They are found mainly in the tropical oceans and seas because they require high mean annual temperature ranging between 20 degrees Celsius to 21 degrees Celsius for survival.
2. Ocean currents and waves are favorable for Coral because they bring the necessary food supply for the polyps.
3. Corals do not live in deeper waters because they die in deeper water due to lack of sufficient amount of sunlight and oxygen which are very much required for the growth of coral polyps. The maximum depth for the ideal growth of Corals is 200 to 300 feet.
4. There should be clean sediment-free water because muddy water clogs the mouths of Coral polyps resulting in their death. 
5. It may be pointed out that the Coral polyps required sediment-free water but freshwater is also injurious for the growth of corals this is why Corals avoid coastal lands and live away from the areas of river mouths.
6. A very high proportion of oceanic salinity is injurious for the growth of Coral polyps because such waters contain little amount of calcium carbonate whereas lime is an important food for Coral polyps.

Types of Coral Reefs

The major types of coral reefs are- (1) Fringing Reef, (2) Barrier Reef, and (3) Atoll.

(1) Fringing Reef

 Fringing reefs developed along the continental margins i.e. lying close to shore and extending outward from the mainland. They grow in shallow waters and in areas of low rainfall-runoff primarily on the leeward side. 

Sometimes there is a gap between them and land and thus lagoon is formed between the fringing reef and the land. Such lagoon is called boat channel which is long but narrow. Such fringing reefs are found along Sakau island, southern Florida, etc.

(2) Barrier Reef

The largest coral reefs off the coastal platforms of the continents but parallel to them are called barrier reefs. Barrier Reefs are the largest, most extensive, highest, and widest reefs of all types of coral reefs.  The barrier reefs have narrow gaps at several places to allow the water from the enclosed lagoon to return to the open ocean. Gaps are very useful for shipping and provide the only entrances for ships to enter or leave the lagoon. 

The best-known barrier reef is the Great Barrier Reef off the coast of Queensland, Australia.

(3) Atoll

Atolls are similar to Barrier Reef except that they are circular in shape,  enclosing a small shallow lagoon without any land in the center. It is a ring of narrow growing corals of horseshoe shape and crowned with palm trees. It is generally found around an island. 

Atolls are divided into three types- (a) True Atoll which is characterized by a circular reef enclosing a Shallow lagoon but without an island, (b) Island Atoll having an island in the central part of the lagoon enclosed by a circular reef, and (c)  Coral Island where atoll island does not have an island in the beginning but later on the island is formed due to erosion and deposition by marine waves.

Some of the atolls are Suvadiva in the Maldives, west of Ceylon, atoll of Ellice Island, etc.

The Importance of Coral Reefs

Following are the importance of coral reefs-

• Rainforests of the ocean–

Corals occupy only 0.1 % of the Global sea surface but more than 25% of marine biodiversity is supported by them including fisheries and other marine animals. Coral reefs are extremely productive ecosystems and are called the rainforests of the ocean as they are more diverse than the tropical rainforest. They provide shelter to various marine animals and fishes. Thus they are an example of rich marine biodiversity.

• Resisting agent to the shoreline areas–

As corals grow in open seas and oceans, they protect the shoreline erosion and reduce flooding in the land areas.  Instead, they contribute to the land accretion. They similarly work like mangroves in the protection of coastal areas.

• Economic value–

Coral reefs support human life and livelihoods and are therefore important economically. According to the World Wildlife Fund (WWF), 1 square kilometer of well-managed coral reef can yield an average of 15 tons of fish and other seafood annually.

Further coral reefs support the tourism industry in countries like Seychelles and Maldives and generate a higher income and employment opportunities through tourism.

• Indicative Species–

Corals are a true indicator of marine heat or pollution. It may be pointed out that they cannot survive in the waters having either very low temperature or very high temperature. Polluted ocean water results in the death of corals as it reduces the availability of oxygen for them.

• An example of mutualism–

As corals form a symbiotic relationship with Zooxanthellae algae who provide food to coral polyps and in return coral shelters them. Thus they are a perfect example of mutualism.

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Threat to Corals

There are several threats faced by corals including-

• Climate Change and its Impact on Coral Reefs-

With rising global temperatures, mass coral bleaching events and infectious disease outbreaks have become more frequent. Any fluctuation in the mean annual temperature is a threat to their survival. Thus the impact of global warming and marine heatwaves has serious repercussions for them.

• Ocean Acidification-

Carbon dioxide absorbed into the ocean from the atmosphere has been reducing calcification rates in reef-building by changing the chemical properties of seawater and making it more difficult for corals to form their shells and skeletons. This can ultimately lead to the dissolving of coral reefs.

• Marine Pollution- 

The dumping of plastics and other medical waste into the open ocean creates a serious problem for their existence.  Further oil spills from cargo ships increase the concentration of various chemical contaminants in the ocean can create a threat to the survival of coral species.

• Overfishing and Destructive Fishing Practices-

Destructive fishing practices such as purse seining, fine-mesh fishing, ‘Moxy nets’, cyanide fishing, and blast fishing result in unsustainable damage to coral reefs or the loss of their habitat.  poorly managed tourism such as sea diving and boating can cause direct physical damage to reefs. Invasive species also pose threat to the survival of corals. The illegal trade of corals also emerged as a major challenge for this ecosystem.

• ENSO-

El-Nino Southern Oscillation (ENSO) is one of the most important climate phenomena on Earth due to its ability to change the global atmospheric circulation, which in turn, influences temperature and precipitation across the globe.  The consequent exposure to high or low temperature increased solar radiation, and seawater dilution by heavy rains could lead to zooxanthellae loss and also cause coral death.

Thus anthropogenic activities such as marine pollution, destructive fishing practices, cyanide blasting, Coral mining, deforestation, industrialization, unregulated tourism, illegal trade, etc., and natural conditions like global warming, marine heatwaves, ocean acidification, climate change, etc. adversely affect corals in their habitats.

Coral Bleaching

Coral bleaching is a process that causes the loss of vivid colors from the coral organisms and turns them white due to the expulsion of symbiotic zooxanthellae algae which are embedded in the tissues of the outer bodies of living corals. It causes mass coral death and the destruction of living corals. 

Studies have shown that coral bleaching begins when the temperature rises 1 Degree Celsius above normal temperature. There is a serious ecological impact of bleaching resulting into the destruction of marine species diversity and reducing their food availability.

Coral bleaching has occurred at a large scale off the coast of West Asia, East Africa, Southeast, and East Asia, in the Indian Ocean, East Pacific, the Caribbean sea, and the Atlantic Ocean.

Global Initiatives Regarding Coral Protection

Several international initiatives have been taken for the protection of coral reefs such as International Coral Reef Initiative, Coral Triangle Initiative, Global Coral Reef Monitoring Network, International Coral Reef Action Network, etc.

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