The Great Barrier Reef’s recovery and vulnerability to climate threats

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The Great Barrier Reef’s recovery and vulnerability to climate threats

  • The highest levels of coral cover, within the past 36 years, has been recorded in the northern and central parts of Australia’s Great Barrier Reef (GBR), according to the annual long term monitoring report by the Australian Institute of Marine Science (AIMS).
  • This could be quickly reversed owing to rising global temperatures. This came after the reef experienced a mass coral bleaching event in March this year.

Coral reefs:

  • Corals are marine invertebrates or animals which do not possess a spine. They are the largest living structures on the planet. Each coral is called a polyp and thousands of such polyps live together to form a colony, which grow when polyps multiply to make copies of themselves.
  • Corals are an example of symbiotic relationship between 2 species: the cnidarian Coral polyp and the microscopic algae Zooxanthellae.
  • The algae prepares food for corals through photosynthesis and also gives them their vibrant colouration while the polyp provides the algae with a solid substrate to grow on

Types of corals

  • Corals are of two types — hard corals and soft corals.
  • Hard corals extract calcium carbonate from seawater to build hard, white coral exoskeletons. Hard corals are in a way the engineers of reef ecosystems and indicate the condition of coral reefs.
  • Soft corals attach themselves to such skeletons and older skeletons built by their ancestors. Soft corals also add their own skeletons to the hard structure over the years. These growing multiplying structures gradually form coral reefs.

Great Barrier Reef (GBR)

  • A UNESCO World Heritage Site (WHS).
  • World’s largest reef system stretching across 2,300 km and having nearly 3,000 individual reefs.
  • It hosts 400 different types of coral, gives shelter to 1,500 species of fish and 4,000 types of mollusc.
  • Coral reefs support over 25% of marine biodiversity even as they take up less than 1% of the seafloor. This is why coral reefs are also called at Marine Rainforests of the world.

Findings of the Report

  • The new survey shows record levels of region wide coral cover in the northern and central GBR since the first ever AIMS survey was done.
  • The record levels of recovery, the report showed, were fuelled largely by increases in the fast growing Acropora corals, which are a dominant type in the GBR.
  • Incidentally, these fast growing corals are also the most susceptible to environmental pressures such as rising temperatures, cyclones, pollution, crown of thorn starfish (COTs) attacks which prey on hard corals and so on.
  • Also, behind the recent recovery in parts of the reef, are the low levels of acute stressors in the past 12 months — no tropical cyclones, lesser heat stress in 2020 and 2022 as opposed to 2016 and 2017, and a decrease in COTs outbreaks.

Mass bleaching events:

  • 1998: El Niño weather pattern caused sea surfaces to heat, causing 8% of the world’s coral to die.
  • 2002: The second event took place
  • 2014-2017: longest and most damaging bleaching event took place.
  • According to the Australian government’s scientists, 91% of the reefs it had surveyed in March were affected by bleaching. Notably, half of the total reefs were surveyed before the peak of this year’s mass coral bleaching event in the GBR.
  • The AIMS report says that the prognosis for the future disturbance suggests an increase in marine heatwaves that will last longer and the ongoing risk of COTs outbreaks and cyclones.


  • Hence the current coral reef recover in GBR is a news of cautious optimism. The reefs are not yet out of the woods.
  • Countries across the world must make united efforts to reduce the level of global warming in order to give a chance to the world’s ‘marine rainforests’.

Prelims Take Away

  • Coral Reefs
  • Types of Coral
  • GBR
  • Coral Bleaching
  • El-Nino