Two-thirds of Australia’s Great Barrier Reef has its largest coral reef in 36 years, an official monitoring program announced Thursday, but the reefs are still suffering from frequent mass bleaching.
Recovery in the central and northern regions of the United Nations Educational, Scientific and Cultural Organization (UNESCO)-listed coral reefs is in stark contrast to the southern region, the Australian Institute of Marine Science said in its annual report. Sees loss of coral cover due to proliferation of spiny starfish.
“This shows how vulnerable coral reefs are to persistent and severe disturbances, occurring rapidly and over long periods of time,” Paul Hardesty, the institute’s executive director, said in a statement.
The report comes as UNESCO is considering whether to classify the Great Barrier Reef as “in danger” after its experts visited it in March. A meeting of the World Heritage Committee with the fate of coral reefs on the agenda was scheduled for June in Russia but was postponed.
In an important measure of coral reef health, the Australian Institute of Marine Science rates hard corals covering more than 30 percent of the area as high value, based on long-term surveys.
In the northern region, average hard coral cover has grown from a low of 13 percent in 2017 to 36 percent in 2022, while in the central region it has risen from a low of 12 percent to 33 percent in 2019, the highest levels recorded in both since the agency began monitoring barrier reefs in 1985.
The southern region, which generally has more hard coral than the other two regions, shrank from 38 percent in 2021 to 34 percent in 2022.
The fourth mass bleaching in seven years and the first recovery comes during a La Niña event, but Hardesty said despite the intensity of the bleaching, 2020 and 2022 are not as damaging as they were in 2016 and 2017.
“These results show that coral reefs can still recover during periods without severe disturbance,” he added.
The downside, however, is that cover growth is driven by a type of coral known as apical corals, which are vulnerable to damage by waves, thermal stress and spiny starfish, the Australian Institute of Marine Science said.
“This means that large increases in hard coral cover can be rapidly modified by disturbances in reefs dominated by the tip pore type,” said Mike Emsley, head of the institute’s monitoring program.