Fourth Global Coral Bleaching

Prelims – General issues on Environmental ecology, Bio-diversity

Mains (GS III) – Environmental Conservation, environmental pollution and degradation.

Why in news?

Recently, scientists have confirmed that the world is experiencing its fourth global coral bleaching event, which has affected nearly 84% (83.7%) of the planet's coral reef area.

• Coral reefs – A coral reef is an underwater ecosystem formed of colonies of coral polyps.
• They are referred to as Rainforests of the sea and it supports 1/3^rd of global marine species.
• Symbiotic Relationship – Corals rely on microscopic algae (zooxanthellae) living in their tissues, which provide food and energy through photosynthesis.
• Global Distribution – Coral reefs exist in the Pacific, Atlantic, and Indian oceans.
• Australia’s Great Barrier Reef is the largest in the world.
• Coral bleaching – It is caused when the when reef water remains too hot for too long, putting corals under stress.
• The stress compels corals to expel marine algae (zooxanthellae) residing inside their tissues.
• These algae provide food and energy from the sun through photosynthesis.
• Once the algae are expelled, corals turn white (bleaching), exposing their skeleton and makes corals vulnerable to diseases.
• Prolonged and extreme heat exposure leads to coral mortality.
• Corals can recover from bleaching in conducive environments, but recovery can take years or even decades.
• Global bleaching events – It is the widespread mass bleaching of Coral reefs that affects coral reefs area globally.
  • 1^st global coral bleaching event (1998) - 21%
  • 2^nd global coral bleaching event (2010) - 37%
  • 3^rd global coral bleaching event (2014-2017) - 68%
  • 4^th global coral bleaching event (2023-2025) - 83.7%
• Mass coral bleaching has been recorded in at least 83 countries and territories.
• This is the most widespread global bleaching event surpassing the previous global bleaching event.
• Causes – Record high ocean temperatures that remains elevated over a period of time across the Pacific, Atlantic, and Indian oceans.
• Climate models predicts that nearly every coral reef on the planet will experience annual bleaching events between 2040 and 2050.

• The Great Barrier Reef is currently undergoing its 6^th mass bleaching event, with its 1^st mass bleaching occurred in 1998.
• This is the 2^nd time the Great Barrier Reef has experienced consecutive bleaching events, with the first being in 2016-17.

Reference

Down to Earth| Mass Global Bleaching Event