Defence Current Affairs: Bleaching of Great Barrier Reef

The Great Barrier Reef located in Australia is currently experiencing its third mass bleaching in just five years — and it is the most widespread bleaching event ever recorded.

The first mass bleaching recorded on the Great Barrier Reef was in 1998, with the next in 2002. But bleaching events in 2016, 2017 and now 2020 have scientists seriously concerned, as there has been little time for reefs to recover in between.

While 40 percent of the reef remained untouched, 25 percent experienced severe bleaching, and 35% was moderately bleached for the first time, we have seen bleaching in all three regions of the reef — the north, the middle and the south.

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What are Coral reefs?

• Coral reefs are the massive underwater structures and they are made of the skeletons of colonial marine invertebrates called coral.
• They are also called as the tropical rainforest of the sea, occupy just 0.1% of the ocean's surface but are home to 25% of marine species. Corals are generally found in shallow areas at a depth less than 150 feet. However, some coral reefs extend even more profound, up to about 450 feet.
• Corals thrive in tropical waters [30°N and 30°S latitudes, The temperature of the water is around 20°C] where diurnal and annual temperature ranges are very narrow.
• The species of corals, responsible for building the reefs are known as hermatypic, or "hard," corals because they extract calcium carbonate from seawater to create a hard, durable exoskeleton that protects their soft, sac-like bodies. 
• Hard corals are dependent on symbiotic algae (zooxanthellae) living within their tissues for nutrition and energy to build their skeleton.

What is Coral Bleaching?

• Zooxanthellae are responsible for giving the corals their colour. When the zooxanthellae are throw out, the coral loses its source of pigmentation, and all that's left behind is the coral's white calcium carbonate skeleton: this white, symbiont-free coral is "bleached.

• Soft corals resemble like colourful plants or graceful trees and are not reef-building it is because they do not produce the hard calcified skeleton of many reef-building corals.
• Each individual coral is called a polyp. They live on the calcium carbonate exoskeletons of their ancestors, adding their own exoskeleton to the existing coral structure.
•  The Great Barrier Reef in Australia is the largest coral reef, more than 1,500 miles long.

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Coral reefs in India

Reason Behind the Bleaching

Natural: Environmental-Temperature, Sediment Deposition, Salinity, pH, etc. Warming water temperatures, induced by climate change, are to blame for this year's bleaching.

Anthropogenic: Mining, Bottom Fishing, Tourism, pollution, etc.

Importance of Corals for Human Race

1. Coral reefs contain staggering biodiversity: Thousands of species can be found living on one reef. The Great Barrier Reef contains over 400 coral species, 1,500 fish species, 4,000 mollusc species and six of the world's seven sea turtle species
2. Coral reefs provide food to millions of people: Coral reefs have an estimated global value of £6 trillion each year, due in part to their contribution to fishing and tourism industries and the coastal protection they provide.
3. Coral reefs protect and create land: The ridges in coral reefs act as barriers and can reduce wave energy by up to 97%, providing crucial protection from threats such as tsunamis.
4. Coral reefs might supply natural medicines: Extracts from animals and plants living on reefs have been used to develop treatments for asthma, arthritis, cancer and heart disease.

Questions asked in Defence exams

1. In India, coral reefs are not found in:

1. Lakshadweep
2. Sunderbans
3. Andaman
4. Gulf of Kutch

2. Which of the following Islands are made of small coral atolls and reefs in the Arabian Sea?

1.  Maldives
2.  Andaman
3.  Sri Lanka
4.  Lakshadweep

Answer the questions in the comment box

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