Video by Grumpy Turtle Films and the Australian Marine Conservation Society. The footage and images were captured at Heron Island, One Tree Island and Sykes Reef in the Capricorn and Bunker group of islands region, at 8-10 metres water depth in late March 2024.

While the fourth global bleaching event was confirmed by researchers last week, scientists working on the Great Barrier Reef have communicated that a widespread mass bleaching event is affecting 75% of local reefs. 

New video footage released by the Australian Marine Conservation Society shows that the coral bleaching on the southern part of the Great Barrier Reef extends to greater depths than has been reported during the current mass bleaching event. Bleached corals have been sited down to at least 18 metres depth and some corals are starting to die as they face record marine heatwaves.

Reef coral expert Dr Selina Ward, the former academic director of the University of Queensland’s Heron Island Research Station, said coral bleaching was extensive at all 16 sites she has just visited across the southern section and described it as the worst she has seen in her 30 years working on the Reef.

Dr Ward said: “I feel devastated. This bleaching event is the worst I have seen. It’s a severe bleaching event. I’ve been working on the Reef since 1992 but this [mass coral bleaching event], I’m really struggling with. The diversity of species involved has been hard to deal with. Look at bleached areas, there are many different species that are bleached – many of which are pretty resistant to bleaching so it’s not a pleasant one.”

On a global level, bleaching-level heat stress, caused by prolonged increases in anomalous ocean temperatures, as remotely monitored and predicted by NOAA’s Coral Reef Watch (CRW), has – and continues to be – extensive across the Atlantic, Pacific, and Indian Oceans. “From February 2023 to April 2024, significant coral bleaching has been documented in both the Northern and Southern Hemispheres of each major ocean basin,” said Derek Manzello, Ph.D., NOAA CRW coordinator.

Mass bleaching of coral reefs, since early 2023, has been confirmed in at least 53 countries, territories, and local economies, including Florida (U.S.A), the Caribbean, the Eastern Tropical Pacific (including Mexico, El Salvador, Costa Rica, Panama, and Colombia), Australia’s Great Barrier Reef, large areas of the South Pacific (including Fiji, Vanuatu, Tuvalu, Kiribati, and the Samoas), the Red Sea (including the Gulf of Aqaba), the Persian Gulf, and the Gulf of Aden.

Bleaching must be confirmed within each ocean basin to make a final determination of a global bleaching event. Reports have now been confirmed of widespread bleaching across parts of the Western Indian Ocean, including Tanzania, Kenya, Mauritius, the Seychelles, Tromelin, Mayotte, and off the western coast of Indonesia.

“As the world’s oceans continue to warm, coral bleaching is becoming more frequent and severe,” Manzello said. “When these events are sufficiently severe or prolonged, they can cause coral mortality, which can negatively impact the goods and services coral reefs provide that people depend on for their livelihoods.”

Where coral bleaching results in mortality, especially on a widespread scale, it impacts economies, livelihoods, food security, and more. However, it is important to remember that coral bleaching does not always lead to coral death. Rather, if the stress driving the bleaching diminishes, corals can recover, with reefs maintaining their biodiversity and continuing to provide the ecosystem services that we rely on.

“Climate model predictions for coral reefs have been suggesting, for years, that bleaching impacts would increase in frequency and magnitude as the oceans warm,” said Jennifer Koss, director of NOAA’s Coral Reef Conservation Program (CRCP).