GS 3: Environment |Conservation, Environmental Pollution & Degradation

Why in News?

  • The world’s southernmost coral reef has been hit by bleaching this summer, Australian scientists said, as they warned rising sea temperatures from climate change were affecting even the most isolated ecosystems.
  • The corals off Lord Howe Island — some 600 km offshore from Sydney — were affected by elevated temperatures this summer, despite escaping severe bleaching that damaged the Great Barrier Reef in 2016 and 2017.

Coral bleaching:

  • The stunning colours in corals come from a marine algae called zooxanthellae, which live inside their tissues.
  • This algae provides the corals with an easy food supply thanks to photosynthesis, which gives the corals energy, allowing them to grow and reproduce.
  • When corals get stressed, from things such as heat or pollution, they react by expelling this algae, leaving a ghostly, transparent skeleton behind.
  • This is known as ‘coral bleaching’. Some corals can feed themselves, but without the zooxanthellae most corals starve.

Can coral recover from bleaching:

  • In some instances, corals can recover from bleaching. If conditions return to normal, and stay that way corals can regain their algae, return to their bright colours and survive. However prolonged warmer temperatures and other stressors, like poor water quality, can leave the living coral in a weakened state.
  • It can struggle to regrow, reproduce and resist disease – so is very vulnerable to coral diseases and mortality.
  • It can take decades for coral reefs to fully recover from a bleaching event, so it is vital that these events do not occur frequently.
  • If we continue burning fossil fuels at our current rate then severe bleaching events are likely to hit reefs annually by the middle of the century. This would be devastating for coral reefs as they would have no chance to recover.


  • Change in Ocean Temperature
  • Runoff and Pollution
  • Overexposure to sunlight
  • Extreme low tides
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