Renowned scientist Terry Hughes says huge swathes of reef have been affected in a ‘severe’ situation
The Great Barrier Reef has experienced a third mass coral bleaching event in five years, according to the scientist carrying out aerial surveys over hundreds of individual reefs.
With three days of a nine-day survey to go, Prof Terry Hughes told Guardian Australia: "We know this is a mass bleaching event and it’s a severe one."
It follows the worst outbreaks of mass bleaching on record killing about half the shallow water corals on the world’s biggest reef system in 2016 and 2017.
Hughes, director of the ARC Centre of Excellence for Coral Reef Studies at James Cook University and one of the world’s leading authorities on bleaching and the Great Barrier Reef, said: "We know enough now that [the bleaching] is more severe than in 1998 and 2002. How it sits with 2016 and 2017 we are not sure yet."
He said a fuller picture would be possible after the final three days of surveying. “They are crucial,” he said.
Working with a staff member from government agency the Great Barrier Reef Marine Park Authority (GBRMPA), Hughes has assessed bleaching levels on 682 reefs from a spotter plane flying at about 500 feet.
Global heating caused by escalating atmospheric greenhouse gases is a major threat to the world’s coral reef ecosystems. The UN’s Intergovernmental Panel on Climate Change found the published evidence suggested a majority of tropical coral reefs would disappear even if heating was limited to 1.5C and would be “at very high risk” at 1.2C. The globe has warmed about 1C since the industrial revolution.
Not all bleached corals die. Corals bleach when they sit in waters that are unusually hot for too long. They can recover if temperatures fall, but are often killed when high temperatures are sustained.
Hughes said the first four days of aerial surveys last week covered almost 500 reefs from the Torres Strait to Cairns. They revealed a mixed picture, with some severe bleaching on reefs closer to shore, but outer "ribbon reefs" in the far north escaping damage.
He said surveys this week in the central parts of the reef had found extensive bleaching at levels "comparable to 2017", when it is estimated about 22% of shallow water coral along the reef’s 2300km died.
Hughes said about 80 reefs between Tully and Townsville were badly bleached. Both inner and outer reefs were hit. "We could see that some of those corals were big enough that they must have survived the 2017 bleaching and now they re-bleached," he said.
Full article on The Guardian
