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29th March 2022 (6 Topics)

The phenomenon of coral bleaching


Great Barrier Reef in Australia has been hit by sixth coral mass bleaching. It is the 4th mass bleaching event since 2016.


About Great Barrier Reef:

  • The Great Barrier Reef is the world’s most extensive coral reef system.
  • It stretches for more than 2,300 kilometres along the northeast coast of Australia.
  • The Great Barrier Reef is home to around 1,500 species of fish and 4,000 types of mollusc.
  • It also holds great scientific interest as the habitat of species such as the dugong (‘sea cow’) and the large green turtle, which are threatened with extinction.
  • No other World Heritage property contains such biodiversity.
  • This diversity, especially the endemic species, means the GBR is of enormous scientific and intrinsic importance, and it also contains a significant number of threatened species.

Coral reefs

  • Coral reefs are large underwater structures composed of the skeletons of colonial marine invertebrates called coral.
  • The coral species that build 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 rely on symbiotic algae (zooxanthellae) living within their tissues for nutrition and energy to build their skeleton.
  • Soft corals look like colourful plants or graceful trees and are not reef-building since they do not produce the hard calcified skeleton of many reef-building corals.
  • These types of corals are flexible organisms often resembling plants and trees and include species such as sea fans and sea whips
  • These types of corals are flexible organisms often resembling plants and trees and include species such as sea fans and sea whips.
  • Each individual coral is referred to as a polyp.
    • Coral polyps live on the calcium carbonate exoskeletons of their ancestors, adding their own exoskeleton to the existing coral structure.
  • As the centuries pass, the coral reef gradually grows one tiny exoskeleton at a time, until they become massive features of the marine environment.

About Coral Bleaching:

  • Corals feed on algae. Coral bleaching takes place when sea temperature rises and destroys the algae. Due to this reason, corals turn white.
  • If water conditions don’t improve, corals can starve and die which turns them white as its carbonate skeleton is exposed.
  • The first incident of mass bleaching took place almost 24 years back in
    • The last mass bleaching was reported in The mass bleaching also occurred in 2002, 2016, and 2017.
    • The United Nations began a monitoring mission to assess whether the Great Barrier Reef, which is also a World Heritage site, is being protected from climate change.
  • The mass bleaching event is the first to happen under the La Niña weather phenomenon which was thought to offset warming ocean temperatures by bringing cooler water to the region.
  • More than half of the living coral cover that we can see from the air is severely bleached completely white and can have signs of fluorescence in the colors of pink, yellow and blue.
    • The corals are producing these fluorescent pigments in an attempt to protect their tissue from heat and from the intense sun during these marine heatwaves.

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