Great Barrier Reef Suffers Steepest Coral Decline
The Great Barrier Reef (GBR) has experienced its most severe loss of hard coral cover in nearly 40 years. The 2024 mass coral bleaching event, driven by climate change-induced heat stress, cyclones and crown-of-thorns starfish outbreaks, devastated large parts of the reef. An annual survey by the Australian Institute of Marine Science (AIMS) revealed that nearly half of the surveyed reefs showed a decline in coral cover. The reef faces increasing threats from frequent bleaching and environmental stresses, pushing the ecosystem closer to collapse.
Recent Mass Bleaching Events
The GBR has endured five major mass bleaching events since 2016. The 2024 event was part of the ongoing global bleaching crisis that began in 2023. Surveys between August 2024 and May 2025 covered 124 reefs across northern, central and southern regions. Nearly 48 per cent of reefs showed coral decline, 42 per cent remained stable, and only 10 per cent improved. The bleaching was most intense in northern and central areas, with some reefs experiencing up to 60 per cent bleaching prevalence.
Regional Coral Cover Declines
The northern GBR suffered the largest annual coral loss since monitoring began in 1986, dropping by 24.8 per cent. Lizard Island was among the hardest hit due to record heat stress, cyclones and freshwater floods. The central GBR saw a 13.9 per cent decline, though some reefs showed stability or slight recovery. The southern GBR experienced the sharpest relative loss of 30.6 per cent, driven by extreme heat in the Capricorn-Bunker sector. Storm damage and coral diseases further worsened conditions.
Impact of Crown-of-Thorns Starfish
Outbreaks of the coral-eating crown-of-thorns starfish continue to damage reefs, especially in the Swains sector. These venomous predators feed on corals weakened by heat stress and storms. Their presence complicates recovery efforts by consuming recovering coral colonies and reducing reef resilience.
Vulnerability of Acropora Corals
Fast-growing Acropora corals, which had supported reef recovery from 2017 to 2024, were severely affected by the 2024 bleaching. These corals are highly susceptible to heat stress, cyclones and starfish predation. Their loss weakens the reef’s ability to rebuild quickly after disturbances, increasing ecosystem volatility.
Increasing Frequency and Intensity of Bleaching
Mass bleaching events on the GBR have intensified and become more frequent. Before 1990, such events were rare. Since 2020, the reef has suffered bleaching in 2020, 2022, 2024 and 2025. This rapid recurrence limits coral recovery time. Globally, over 83 per cent of coral reefs experienced bleaching-level heat stress between 2023 and 2025, affecting at least 83 countries.
Long-Term Monitoring and Ecosystem Stress
AIMS’ Long-Term Monitoring Program shows increasing fluctuations in coral cover over the last 15 years. Coral levels now swing between record highs and lows, indicating an ecosystem under severe stress. This volatility challenges the reef’s long-term survival and demands urgent climate action to reduce heat stress and protect marine biodiversity.
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