Cause of coral death off Australia's coast discovered

Australian oceanographers have concluded that the mass death of corals on the Great Barrier Reef was linked to rising surface temperatures in the Pacific Ocean.

This has been the case over the past four centuries, the University of Wollongong's press service reported.

University of Wollongong professor Helen MacGregor said the ocean temperatures recorded were unprecedented in the past four centuries. The Great Barrier Reef is on the verge of collapse due to human-caused global warming, and organisms, including corals that have lived here for centuries, remain at great risk.

The scientists made the discovery while studying samples of coral that have grown on Australia's Great Barrier Reef since the early 17th century. They used the fossilized shells of these ancient polyps to reconstruct changes in surface water temperatures in the Pacific Ocean, among other factors.

This information was made possible because the proportion of strontium and calcium atoms, as well as the proportion of “heavy” oxygen 18, in the protective shells of corals depend largely on the warmth of the water in which the polyps grew. This allows the shells of long-lived corals of the genus Porites to be used to study how environmental conditions change during the life of these polyps.

The scientists analyzed the composition of annual layers in the shells of the oldest and largest corals from the Great Barrier Reef, allowing them to track how temperatures in the Pacific Ocean have changed from 1620 to the present day. These measurements showed that temperatures in recent decades have been about 1.5 degrees Celsius warmer than in the early 17th century, with the hottest years recorded in 2004, 2016, 2017, 2020, 2022 and 2024.

During these same seasons, the researchers noted, there were several episodes of mass coral die-offs on the Great Barrier Reef, suggesting a direct link between warming waters and these events. The researchers say Pacific Ocean temperatures in 2024 will be particularly hot, nearly three degrees warmer than the coldest years in the mid-17th century. The oceanographers concluded that these temperature records have already affected the health of the reefs and led to the destruction of a large number of colonies.