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Current Affairs

Coral bleaching

Date: 31 March 2022 Tags: Climate Change


Australia’s Great Barrier Reef is experiencing a mass coral bleaching event, the management authority has announced.



The Great Barrier Reef is the world’s largest coral reef. It is located on the east-coast of Australia.



The current bleaching event is the sixth bleaching event that has occurred and fourth one in the last six years.


Coral reefs

  • They are invertebrates that are made up of individual animals known as polyp. Multiple polyps form colonies called reefs.

  • The Great Barrier Reefs of Australia stretch across 2,300 km. They sustain an ecosystem consisting of multiple corals, fishes and mollusc.



  • Corals are two types--hard corals and soft corals. Hard corals extract calcium carbonate from sea water to build exoskeletons.

  • Soft corals attach themselves to these skeletons. Over the years, they add their own skeletons to form coral reefs.


Corals share symbiotic relationship with single-celled organism called zooxanthellae. They provide corals nutrients and in turn in they get place to live.


Coral bleaching

  • It is an event in which the coral polyps expel colour-giving zooxanthellae. This exposes their white exoskeleton, giving it a bleached appearance.

  • Due to changing temperature, ocean acidity or pollution, corals experience stress. In such a condition, the algae produce reactive oxygen compounds, resulting in their expulsion.

  • The events are temporary or permanent based on the amount of stress. If the stress conditions subside over time, the algae can come back and their symbiotic relationship survives.

  • If it remains for a longer time, algae do not return. The corals do not receive their food and nutrients, which results in their destruction.

  • Studies have shown that 14% of the world’s corals have died between 2009 and 2018 due to coral bleaching events.



  • Coral reefs take a small amount of space but they support 25% of marine species such as fish, turtles, lobsters etc.

  • Coral reefs are the backbone of fishing industry as they sustain large fish population. Large fishes are also dependent on smaller fishes.

  • They have $2.7 trillion worth economic value due to goods, services and tourism related activities. They protect protection over sea storms.


Status of Great Barrier Reefs

  • Climate change has threatened existence of the reefs. Future bleaching events can destroy the remaining reefs in Australia.

  • The UNESCO had threatened to degrade World Heritage Site listing, after which Australia created “Reef 2050” plan to protect the site.