• Australia’s Great Barrier Reef has suffered the largest decline in coral cover in two of its three regions over the last year, following a mass bleaching of its corals that was among the worst on record.

• The Australian Institute of Marine Sciences said the reef has experienced the largest annual decline in coral cover in its northern and southern regions since monitoring began 39 years ago, with coral cover dropping between a quarter and a third after several years of solid growth.

• Analysis of 124 reefs on the Great Barrier Reef shows coral cover has dropped sharply after a record-breaking marine heatwave in 2024, prompting grave fears over the trajectory of the natural wonder.

• Aerial surveys showed three quarters of 1,080 reefs assessed had some bleaching. On 40 per cent of these reefs, more than half the corals were white.

• Mass coral bleaching is becoming more frequent as the world warms.

• Before the 1990s, mass bleaching was extremely rare. That changed in 1998 with the first major event, followed by another in 2002.

• Back-to-back bleaching events occurred for the first time in 2016 and 2017. Since then, bleaching has struck the Great Barrier Reef in 2020, 2022, 2024, and again this year. 

• The 2024 event had the largest footprint ever recorded on the reef, with high to extreme bleaching across all of its three regions.

• The impacts of this year’s bleaching event will be revealed following the next round of surveys.

What is coral bleaching?

• Coral and algae depend on each other to survive. Corals have a symbiotic relationship with microscopic algae called zooxanthellae that live in their tissues. These algae are the coral’s primary food source and give them their colour.

• If stressed, algae leaves the coral. When the symbiotic relationship becomes stressed due to increased ocean temperature or pollution, the algae leave the coral’s tissue. 

• When water is too warm, corals expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. This is called coral bleaching. When a coral bleaches, it is not dead. 

• Without the algae, the coral loses its major source of food, turns white or very pale, and is more susceptible to disease.

• Corals can survive a bleaching event, but they are under more stress and are subject to mortality.

The Great Barrier Reef

• The Great Barrier Reef is a network of almost 3,000 coral reefs and a diverse array of non-reef habitats stretching 2,300 km along the east coast of Queensland. 

• The Great Barrier Reef World Heritage Area covers an area of 348,000 square kilometres and has connections to the Torres Strait north of Cape York, the Coral Sea and the Great Sandy Strait, adjacent to Fraser Island in the south.

• It is one of the best known and most complex natural systems on Earth, developed over millions of years, and contains a unique range of ecological communities, habitats and species.

• The Reef is an international icon and valued as Australia’s most acclaimed natural asset for its unique biodiversity, cultural significance and immense ecological scale.

• The Reef is critical to the tourism industry and the millions of coastal residents. This immense ecosystem supports an estimated 64,000 jobs and generates an annual income of A$6.4 billion to the Australian economy. Most of this is from tourism, with the Reef attracting more than two million visitors each year from across the globe. 

• It was placed on the World Heritage List in 1981.

• The Reef meets all four of the UNESCO natural criteria for World Heritage listing. It is recognised for its natural beauty and natural phenomena, ecological and biological processes, habitats for conservation of biodiversity and for containing major stages of the Earth’s evolutionary history.

• The Great Barrier Reef is not currently on UNESCO’s list of World Heritage in Danger, though the UN recommends it should be added.

Main threats to the Reef:

• Increasing temperatures are threatening most species and habitats in the Reef ecosystem.

• Reef-dependent industries are affected when poor water quality degrades ecosystems.

• The greatest water quality risks to the Reef and its coastal ecosystems are land-derived inputs from nutrients, fine sediments and pesticides.

• Overfishing of particular species and illegal fishing can impact food chains and ecosystem processes. 

• Marine debris can be eaten by wildlife or entangle them, impacting their health and potentially causing death.

• Artificial light pollution from coastal infrastructure and ships can interrupt the navigation ability of marine species and disturb turtle hatchlings.

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