Drones Reveal Extreme Coral Mortality After Bleaching
New research has revealed coral mortality rates of 92% after last year’s bleaching event at Lizard Island on Australia’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.
Their findings, published in Coral Reefs, 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,” says Professor Jane Williamson from the School of Natural Sciences at Macquarie University, senior author on the study.
The link between short-term bleaching and coral mortality across a larger area was previously hard to assess as it relied on underwater surveys of individual coral colonies.
“Use of this technology lets us upscale the effects of the bleaching event over larger areas but still at high precision,” says Williamson.
Lead author Dr Vincent Raoult from Griffith University’s School of Environment, and collaborators from Macquarie University, James Cook University, the CSIRO and GeoNadir analyzed 20 sections, each measuring 10 meters by 10 meters, across the northern and southern reefs of Lizard Island.
The average bleaching mortality rate was 92%, with bleaching affecting an average of 96% of living corals in the surveyed areas.
The team used DJI Mini 3 Pro and Autel Evo II drones to collect the imagery, verified by in-water observations during June 2024.
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. These events have compounded the ecosystem’s vulnerability, despite some signs of recovery in recent years.