Fourth Global Bleaching Event

Syllabus: GS3/ Biodiversity and Conservation

Context

• The US National Oceanic and Atmospheric Administration in partnership with the International Coral Reef Initiative, confirmed that the world is witnessing its fourth global bleaching event.

About

• The bleaching-level heat stress has impacted 83.7% of the planet’s coral reef area and mass coral bleaching has been recorded in at least 83 countries and territories. 
  • The ongoing global coral bleaching event is the biggest to date. 
• Previous Bleaching: 
  • The 1st and 2nd global coral bleaching events occurred in 1998 and 2010, respectively. 
  • The 3rd global coral bleaching event, which occurred from 2014-2017, when 68.2% of the world’s reef area experienced bleaching-level heat stress. 
• Future Projections: Climate models predict that by 2040-2050, nearly every coral reef worldwide will face annual bleaching events.
• Great Barrier Reef Status: Currently undergoing a sixth mass bleaching event.
  • Second consecutive bleaching episode after 2016-17.
  • Caused by prolonged marine heatwaves, especially in Far Northern and Northern regions.
• Bleaching History in Australia: Mass coral bleaching events recorded in 1998, 2002, 2016, 2017, 2020, 2022, and 2024.

What are Corals?

• Corals are invertebrates that belong to a large group of animals called Cnidaria.
  • Corals are formed by multiple small, soft organisms known as polyps. 
  • They secrete a rocky chalk-like (calcium carbonate) exoskeleton around themselves for protection. 
  • Coral reefs are therefore created by millions of tiny polyps forming large carbonate structures.
• Appearance: Corals range in colour from red to purple and even blue, but are most commonly shades of brown and green.
  • Coral are bright and colorful because of microscopic algae called zooxanthellae.
• There are three types of coral reefs – fringing reefs, barrier reefs and atolls.
  • Fringing reefs form along shorelines, barrier reefs form in open water and atolls are circular reefs that have formed around sunken volcanoes.

Coral Bleaching

• Coral bleaching occurs when corals expel the colourful algae living in their tissues. 
• Without these helpful algae, the corals become pale and are vulnerable to starvation and disease. 
• A bleached coral is not dead, but ocean temperatures need to cool off for any hope of recovery.
• At least 14% of the world’s remaining corals were estimated to have died in the previous two global bleaching events.

What triggers Coral Bleaching?

• The leading cause of coral bleaching is climate change. 
  • A warming planet means a warming ocean, and a change in water temperature—as little as 2 degrees Fahrenheit—can cause coral to drive out algae. 
• Coral also bleaches for other reasons, like extremely low tides, pollution, or too much sunlight.

Concerns

• Coral bleaching matters because once these corals die, reefs rarely come back. 
• With few corals surviving, they struggle to reproduce, and entire reef ecosystems, on which people and wildlife depend, deteriorate.
• This would have dire implications for ocean health, subsistence fisheries and tourism. 

Impact of Coral Bleaching

• Wildlife: Thousands of marine animals depend on coral reefs for survival.
  • Coral reefs provide shelter, spawning grounds, and protection from predators. 
  • They also support organisms at the base of ocean food chains. 
  • As reef ecosystems collapse, already at-risk species may face extinction.   
• Humans: Coral reefs are natural barriers that absorb the force of waves and storm surges, keeping coastal communities safe. 
  • Every year, reefs provide about $2.7 trillion in goods and services, according to a 2020 estimate by the Global Coral Reef Monitoring Network.
  • Bleached coral also compounds the overfishing crisis by removing links in the food web and depriving some fish of a place to spawn and develop.
  • Reef tourism brings in billions of dollars each year and supports thousands of jobs. 

Can corals recover from bleaching?

• Corals can recover if conditions improve, but recovery can take years or even a decade, depending on the extent of the damage.
• Corals can recover only if temperatures drop and conditions return to normal. 
• When this happens, the algae returns and the corals gradually regain their health.

Way Ahead

• Strengthening Marine Protected Areas (MPAs).
• Implementing coral restoration techniques, such as coral gardening and breeding resilient coral species, to enhance recovery after bleaching events.
• Advocating for global efforts to reduce greenhouse gas emissions to limit temperature increases and ocean acidification.
• Increasing investment in research to better understand coral resilience, bleaching triggers, and recovery processes, alongside developing advanced monitoring technologies.

Source: DTE