Why in News?

• According to the U.S. NOAA, the world is on the verge of a fourth mass coral bleaching event which could see wide swathes of tropical reefs die, including parts of Australia's Great Barrier Reef.

What’s in Today’s Article?

• What are Corals and Coral Reefs?
• What is Coral Bleaching and Why is it a Cause for Concern?
• What are the Findings of the National Oceanic and Atmospheric Administration (NOAA)?

What are Corals and Coral Reefs?

• Corals are animals (polyps), which live in a symbiotic relationship with tiny algae called zooxanthellae.
  • These algae provide the corals with food and oxygen, and in return, the corals provide them with a safe place to live.
• Coral reefs are limestone structures formed by thousands of tiny coral animals and are found in tropical climates.
• Major coral reefs in India:
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What is Coral Bleaching and Why is it a Cause for Concern?

• When corals are exposed to stressful conditions, such as high temperatures, pollution, or changes in the water’s chemistry, they expel the zooxanthellae.
• Without them, the coral loses its color and turns white, hence the term “bleaching.” Corals cannot live very long in this state.
• Coral bleaching doesn’t necessarily mean the end of the reef. If the stressor is removed in time, the zooxanthellae can come back and the corals can recover.
• Coral reefs provide a home and a source of food for countless species of fish and other marine creatures.
• They also protect coastlines from erosion and storms, and play a vital role in regulating the Earth’s climate by absorbing and storing carbon dioxide.
• Additionally, coral reefs are a stunning display of biodiversity and natural beauty, and their loss would be a tragedy for future generations.
• When coral reefs suffer, so do the ecosystems and the people that depend on them.

What are the Findings of the National Oceanic and Atmospheric Administration (NOAA)?

• The world is on the verge of a fourth mass coral bleaching event (after 1998, 2010 and 2014).
• For an event to be deemed global, widespread bleaching must occur in three ocean basins - the Atlantic, Pacific and Indian.
• The last global mass coral bleaching event ran from 2014 to 2017, during which time the Great Barrier Reef lost nearly a third of its corals.
  • Preliminary results suggest that about 15% of the world's reefs saw large coral die-offs in this event.
• This year is turning out to be even worse. For example, following the Northern Hemisphere summer last year, the Caribbean registered its worst coral bleaching on record.
• Coral bleaching is often tied to the naturally occurring El Nino climate phenomenon which leads to warmer ocean waters.
• The world also just registered (as a result of climate change) its first 12-month period with an average temperature over 1.5 degrees Celsius (2.7 degrees Fahrenheit) above pre industrial levels.
  • A rise of 1.5C is believed to be the tipping point for mass coral die-offs, with scientists estimating that 90% of the world's corals could be lost.