SYDNEY: The Great Barrier Reef has recorded its sharpest decline in coral cover in 39 years, with scientists blaming climate change-driven heatwaves, tropical cyclones, and coral-eating starfish outbreaks for the devastation. The 2024 mass bleaching event has now become the most widespread ever documented, leading to over 70% loss in hard coral cover in some regions.
According to the Australian Institute of Marine Science (AIMS), this marks the fifth mass bleaching since 2016, and part of the ongoing global coral bleaching crisis that began in 2023.
AIMS surveyed 124 reefs between August 2024 and May 2025. The findings were stark:
•48% of reefs saw a decline in coral cover.
•42% remained unchanged.
•Only 10% showed recovery.
The northern GBR, especially around Lizard Island, was the hardest hit, with average coral cover dropping nearly 25% in just one year. The central region also saw declines due to Cyclone Jasper and associated flooding. The southern GBR suffered a record 30.6% drop, mainly due to record heat stress in the Capricorn-Bunker sector.
Fast-growing Acropora corals, known for helping reefs bounce back, were among the worst affected. They are especially vulnerable to heat stress, disease, and predation by the crown-of-thorns starfish.
Scientists now say the resilience of the reef is weakening. “We’re seeing extreme fluctuations in coral cover in short intervals, reflecting an ecosystem under severe stress,” said AIMS LTMP head Mike Emslie.
AIMS Chief Executive Selina Stead warned that mass bleaching is becoming a near-annual event, with back-to-back bleaching years (2024 and 2025) a dangerous new trend. “The reef is losing its ability to recover,” she said.
Globally, the NOAA reports that over 83% of coral reefs worldwide have been exposed to bleaching-level heat stress in the past two years, affecting at least 83 countries and territories.
As scientists continue to raise the alarm, they say climate action is now urgent and non-negotiable. Without drastic reductions in greenhouse gas emissions and improved marine protection, the world’s largest coral reef system a UNESCO World Heritage Site could face irreversible collapse within decades.