Coral Bleaching Events Becoming More Frequent

Syllabus: GS3/ Biodiversity and Conservation

Context

• The seventh Status of Coral Reefs of the World report by the Global Coral Reef Monitoring Network (GCRMN) said recovery periods had shortened dramatically.
  • Coral reefs are facing bleaching events more frequently, leaving them less time to recover between periods of severe heat stress.

Major Highlights

• Major disturbances are occurring every four to six years in many regions after 2010, compared with roughly once a decade in the past. 
• Global hard coral cover has declined by an estimated 9.5% compared with the 1980–2009 reference period.
• More than 40% of reefs experienced heat stress severe enough to risk bleaching and mortality in 2024.
• The report warned that marine heatwaves, driven by climate change and compounded by local pressures, could push reefs towards sustained decline.
  • Without significant reductions in greenhouse gas emissions, global warming would exceed 2 degrees Celsius and marine heatwaves would persist and intensify, causing further declines in coral reefs.

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 reefs in India: Gulf of Kutch, Gulf of Mannar, Andaman & Nicobar, Lakshadweep Island and Malvan.
• Significance: They provide food, shelter, resting and breeding grounds to a quarter of all marine life, acting as nurseries and refuges to protect critical biodiversity.
  • They also support more than 1 billion people living in coastal regions around the world by providing food, livelihoods and recreation.

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.

Reasons for Coral Bleaching

• Marine Heatwaves & Climate Change: Rising sea surface temperatures disrupt the symbiotic relationship between corals and algae, causing mass bleaching and mortality.
• Ocean Acidification: Increased CO₂ dissolving into oceans reduces water pH, making it harder for corals to grow skeletons.
• Pollution: Runoff from land containing fertilizers, pesticides, and heavy metals like lead damages coral health and resilience.
• Physical Disturbance: Coastal development, unsustainable fishing, sedimentation, and coral mining physically damage or smother reefs.
• Overfishing: Reduces fish populations that control algae growth on reefs, further degrading coral environments.

Can corals recover from bleaching?

• Corals can recover from bleaching over time, but only if temperatures drop and conditions return to normal. 
• When this happens, the algae returns and the corals gradually regain their health.

Source: DTE