Coral Reefs

Coral Reefs

Subject – Environment

Context – The world’s coral reefs have suffered terribly in 30 years, but are resilient.

Concept –

• Coral reefs have suffered terribly in the past three decades. Yet, they are resilient and would be able to withstand challenges posed by a warming world, a recent study by the Government of Australia has said.
• The study also said reducing local pressures on coral reefs to maintain their resilience would be critical in the years to come.
• Status of Coral Reefs of the World: 2020 was prepared by the Global Coral Reef Monitoring Network, along with the Australian government.
• There were many shocking aspects noted in the report as well. For instance, the 1998 coral bleaching event killed eight per cent of the world’s coral.
• Subsequent events between 2009 and 2018 killed 14 per cent of the world’s coral.
• Most declines in global coral cover were associated with either rapid increase in sea surface temperature (SST) anomaly or sustained high SST anomaly.
• There were 20 per cent more algae on the world’s coral reefs in 2019 than in 2010. The increase in the amount of algae, was associated with declines in the amount of hard coral, the study said.
• The study noted that since 2010, almost all regions had exhibited a decline in average coral cover. According to estimates, coral reefs would experience further declines in the coming decades as sea temperatures arose.
• However, the increases in global coral cover between 2002 and 2009 and in 2019 offered hope. It showed that coral reefs globally remained resilient and could recover if conditions permitted.
• For instance, coral reefs in East Asia, which has 30 per cent of the world’s coral reefs, had more coral on average in 2019 than they did in 1983. This, despite the area being affected by large-scale coral bleaching events during the last decade.

About Coral Reefs –

• Coral reefs are one of the most biologically diverse marine ecosystems on the Earth.
• Coral reefs play an important role in marine ecosystems and support the habitats of flora and fauna in the sea.
• 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.
• Coral polyps are the individual corals that are found on the calcium carbonate exoskeletons of their ancestors.
• Corals can be found in all the oceans but the biggest coral reefs are mostly found in the clear, shallow waters of the tropics and subtropics.
• The largest of these coral reef systems, The Great Barrier Reef in Australia, the largest coral reef is more than 1,500 miles long.

Coral Reefs in India –

• Coral reefs are present in the areas of Gulf of Kutch, Gulf of Mannar, Andaman & Nicobar, Lakshadweep Islands and Malvan.

Largest Coral Reef Area:

• Indonesia has the largest coral reef area in the world.
• India, Maldives, Sri Lanka and Chagos have the maximum coral reefs in South Asia.
• Great Barrier Reef of the Queensland coast of Australia is the largest aggregation of coral reefs.

Major threats for the corals

• Natural: Environmental-Temperature, Sediment Deposition, Salinity, pH, etc
• Anthropogenic: Mining, Bottom Fishing, Tourism, pollution, etc.

Types of Coral Reefs

Coral Bleaching –

• The coral and the zooxanthellae share a symbiotic relationship and 90% of the nutrients that are produced by the algae are transferred to the coral hosts.
• But this relationship gets affected under severe environmental stress which causes the loss of symbiotic algae (zooxanthellae).
• As a result, the white calcium-carbonate exoskeleton is visible through its transparent tissue leading to a condition known as Coral Bleaching.
• The corals become vulnerable in the absence of the algae and begin to die if the temperature of the sea remains high for weeks.