Context: Scientists have warned that the Great Barrier Reef(GBR) will face a critical period of heat stress over the coming weeks, following the most widespread coral bleaching the natural world has ever endured.

About GBR:

  •  The Great Barrier Reef Marine Park, which spreads across a length of over 2,300 km and is roughly the size of Italy, is home to about 3,000 coral reefs, 600 continental islands, 1,625 types of fish, 133 varieties of shark and rays and 600 types of soft and hard corals.
  • Warming ocean temperatures, a sign of climate change, is associated with the deteriorating health of the Reef.

Importance of GBR:

The Great Barrier Reef, which covers roughly 10 percent of the world’s coral reef ecosystems- 

  • Supports a range of activities and contributes over AUD $5.6 billion each year to the Australian economy and 
  • is also responsible for creating over 70,000 jobs.

Threats to GBR:

In the 2019 Outlook Report prepared by the Australian government, it said that 

  • Climate change was the greatest threat to the Reef. 
  • Other threats included 
    • coastal development,
    • land-based run-off and
    • direct human use, such as activities like illegal fishing.

What is coral bleaching?

Image Source: https://oceanservice.noaa.gov

  • According to the National Oceanic and Atmospheric Administration (NOAA), when corals are stressed by changes in conditions such as temperature, light or nutrients, they expel the algae living in their tissue, causing them to turn white, hence bleached.
  • Coral bleaching does not mean the corals are dead, but make them vulnerable, hence increasing their mortality. 
  • Warm ocean temperatures are one condition that could lead to coral bleaching. For instance, in 2005, the US lost half of its coral reefs in the Caribbean in one year due to a massive bleaching event.
  • According to the NOAA, not all bleaching events are due to warmer temperatures. For example, in 2010 cold water temperatures in the Florida Keys caused a coral bleaching event that resulted in some coral deaths.

How does it affect the Great Barrier Reef?

  • Significantly, coral bleaching events such as the ones that took place in 2016 and 2017 have had severe impacts on the Reef, causing changes in its ecosystem
  • However, some parts of the reef that escaped the impact of the bleaching and cyclones still remain in good condition, the report said.


Coral Reef

  • Corals are animals in the same class (Cnidaria) as jellyfish  and anemones. 
  • They consist of individual polyps that get together and build reefs. Coral reefs are important hotspots of  biodiversity in the ocean. 


  • Coral reefs maintain the quality of the coastal   biosphere and support a wide range of species.
  • Corals convert the carbon dioxide in the water into a limestone shell and thus control the level of carbon dioxide in the water. 
  • This maintains the amount of carbon dioxide in the ocean water and thus saves ecological niches from destruction.

Source: https://indianexpress.com/article/explained/great-barrier-reef-coral-bleaching-explained-6303755/