Great Barrier Reef Suffers Its Most Widespread Mass Bleaching Event On Record

An anonymous reader quotes a report from The Washington Post: Surveys conducted by scientists at Australia’s James Cook University and the Great Barrier Reef Marine Park Authority show that a summer of extreme heat has caused the reef, which is a World Heritage Site, to suffer a mass bleaching of unprecedented scale. Corals from the far north to the southern tip of the 1,400 mile-long ecosystem are experiencing severe impacts. It was also one of the reef’s worst mass bleaching episodes in terms of intensity, second only to 2016, which killed half of all shallow-water corals on the northern Great Barrier Reef. Unlike the summer of 2016, when an intense marine heat wave coincided with one of the strongest El Nino events on record, this past summer brought a bleaching event without any assistance from the Pacific climate oscillation. As heat built across the reef in February, the Great Barrier Reef Marine Park Authority began reporting pockets of bleaching in the far north toward the end of the month. By early March, vast swaths of the ecosystem had accumulated eight or more “degree heating weeks,” a metric scientists use to describe recent cumulative heat exposure. At this threshold, reef scientists expect to see widespread bleaching and mortality from thermal stress, according to NOAA. Researchers decided to conduct aerial and waterborne surveys to assess the extent of the damage. The surveys, which took place during the last two weeks of March, quickly confirmed the reef has undergone its third mass bleaching event in the past five years. “This year, some 35 percent of the 1,036 reefs the scientists surveyed experienced moderate bleaching, while a quarter were severely bleached,” the report adds. “Scientists saw severe bleaching on coastal reefs from Torres Strait in the far north to the southern border of the Great Barrier Reef Marine Park, at levels only eclipsed during 2016.” What’s troubling to see is bleaching in the south, which has managed to escape the previous two events. “In the northern and central Great Barrier Reef, these corals were largely annihilated by bleaching in 2016-17, transforming vast swaths of the reef into a ‘highly altered, degraded system,'” reports The Washington Post, citing a 2018 paper in the journal Nature. “Now the south seems poised to slide into a similar ecological disrepair.”