What causes coral bleaching on the Great Barrier Reef?
Coral bleaching on the Great Barrier Reef is mainly caused by marine heatwaves. When water stays too warm for too long, corals expel the algae living in their tissues and turn white.
Reef-building corals depend on tiny algae called zooxanthellae, which live inside them, provide food through photosynthesis and give corals much of their colour. Heat stress breaks down this partnership, leaving the white coral skeleton visible through clear tissue.
Bleached corals are not dead, but they are starving. If temperatures fall quickly, many recover their algae within weeks. If the heat lasts, corals can die, and reefs may take a decade or more to recover.
Mass bleaching events
The Great Barrier Reef suffered mass bleaching in 1998 and 2002, and then repeatedly since 2016, with widespread events including 2016, 2017, 2020, 2022 and 2024. Scientists link the rising frequency to warming oceans caused by climate change.
Researchers survey the reef from the air and underwater to map damage. The Great Barrier Reef Marine Park Authority uses this information to guide management.
Reducing local threats such as poor water quality and crown-of-thorns starfish helps corals recover, but scientists say cutting greenhouse gas emissions is the key long-term solution.
Did You Know?
Some corals glow in bright fluorescent colours during bleaching, producing a natural sunscreen as they struggle.