Drones reveal extreme coral mortality after bleaching

New research has revealed alarming coral mortality rates of 92 per cent after last year’s bleaching event at Lizard Island on Queensland’s Great Barrier Reef, marking one of the highest coral mortality rates ever documented globally.  

The team assessed the impact of the Fourth Global Coral Bleaching Event, declared by the National Oceanic and Atmospheric Administration (NOAA) in April 2024, which caused extensive bleaching and mortality across the reef system. 

Lead author Dr Vincent Raoult from Griffith University’s School of Environment, and collaborators from Macquarie University, James Cook University, the CSIRO and GeoNadir analysed 20 sections (each measuring 10m x 10m) across the northern and southern reefs of Lizard Island.  

The average bleaching mortality rate reached was 92 per cent, with bleaching affecting an average of 96 per cent of living corals of the surveyed areas.  

“This marks one of the highest coral mortality rates ever documented globally,” Dr Raoult said. 

“Despite lower heat stress at Lizard Island compared with other parts of the Great Barrier Reef, the mortality rate is unprecedented.  

“These results highlight the fragility of coral ecosystems facing increasing stress from climate change, and the possible devastation resulting from the 2024 global bleaching event.” 

Professor Jane Williamson from the School of Natural Sciences at Macquarie University, senior author on the study, said the findings underscored the urgent need for action on climate change. 

The research team used high-resolution drone imagery to map coral bleaching in March 2024, returning in June to assess survival and mortality rates across the same reef areas. 

“Using drone-derived imagery, we followed the amount of bleached and living coral during and after the  bleaching event,” Professor Williamson said.  

“Use of this technology lets us upscale the effects of the bleaching event over larger areas but still at high precision.” 

The team recorded the highest coral bleaching mortality on the Great Barrier Reef, with over 92 per cent of corals experiencing mortality. 

“Our results are concerning for coral resilience, considering the increasing frequency and intensity of extreme heat events predicted for the near future, with potentially irreversible consequences for reef ecosystems such as those studied in our Great Barrier Reef,” Professor Williamson said. 

The team used DJI Mini 3 Pro and Autel Evo II drones to collect the imagery, verified by in-water observations during June 2024. 

Key findings: 

• Coral reefs at Lizard Island have experienced repeated disturbances over the past decade, including severe bleaching in 2016 and 2017, cyclones, and Crown-of-Thorns outbreaks.  

The team responsible for this work are now running additional surveys at Lizard Island to track the recovery, if any, of corals into 2026 as part of an Australian Museum Lizard Island Critical Grant. 

The study ‘Coral bleaching and mass mortality at Lizard Island revealed by drone imagery’ has been published in Coral Reefs.  

Part of this research was funded by the Grea