Reefs across the north of the Great Barrier Reef have seen “substantial losses” of coral cover after a summer of extreme heat, two cyclones and major flooding, according to the first results of surveys from government marine scientists.
After the most widespread coral bleaching event seen on the world’s biggest reef system, the Australian Institute of Marine Science said one area around Cooktown and Lizard Island had lost more than a third of its live hard coral – the biggest annual drop in 39 years of monitoring.
Dr Mike Emslie, leader of Aims’ long-term monitoring program, described a “graveyard of corals” off Lizard Island, with Linnet Reef one of the worst-hit.
“It was pretty sobering,” he said. “Probably the worst single impact I have seen in 30 years. We saw dead standing coral colonies and the whole scene was a drab brown mess. As far as the eye could see was corals covered in algae.”
Aims revealed the results from in-water surveys of 19 reefs between Cairns and Cooktown carried out in recent months, where 12 reefs saw a drop in coral cover of between 11% and 72%.
The results are the first official assessment of the impact of last summer’s mass coral bleaching event, which came during a fourth global event that saw heat stress high enough to bleach more than 70% of the planet’s corals, affecting reefs in more than 70 countries.
Emslie said mass coral bleaching events were “unheard of” before the late 1990s but were now happening “every other year” on the reef, and this would worsen as global heating continued. The 2024 mass bleaching was the fifth since 2016.