The Great Barrier Reef has suffered its third mass bleaching event in five years as the Australian government aerial surveys have detected widespread bleaching throughout its boundaries.
Though the island nation has seen cooler temperatures lately, a buildup of heat stress over the Australian summer – particularly through February – has led to varying degrees of bleaching across the reef. In-water and aerial surveys conducted by the Australian Government Great Barrier Reef Marine Park Authority in collaboration with the Australian Research Council Centre of Excellence for Coral Reef Studies at James Cook University have so far observed around 344,000 square kilometers (133,000 square miles) from more than 800 reefs. Such surveys have delivered a wide variety of results; some saw no bleaching, others were determined “very severe” with 80 percent or more of corals bleached. The worst bleaching has occurred on reefs that suffered the highest heat stress.
As concerning as many of these results are, it’s definitely not all bad news, said Chief Scientist Dr David Wachenfeld in a weekly reef health update. Pockets of the reef remain unaffected and healthy areas of the reefs are still intact. In fact, all of the offshore reefs had little or no bleaching and there are still many reefs in the southern part of the park that saw little or no bleaching this year.
“It is important to remember bleached corals are not dead corals — on mildly or moderately bleached reefs there is a good chance most bleached corals will recover and survive this event,” writes the agency. “Equally, on severely bleached reefs, there will be higher mortality of corals.” Data collected so far has been compared against information obtained in 2016 and 2017. One-third of the park saw no or minor bleaching, one-third had moderate bleaching, and the remaining third had severe bleaching, though no consistent patterns have been observed.
In the far north, many of the coastal reefs are seeing bleaching for the third time after experiencing moderate-to-severe bleaching in previous survey years. Equally, in the southern half where bleaching did not previously occur, some reefs are now experiencing severe bleaching for the first time. Additionally, some key tourism areas – particularly the northern and central Great Barrier Reef – have only shown moderate bleaching that researchers hope will allow them to recover and survive.
“With aerial surveys being completed this week, we will better understand the extent and severity of this bleaching event. Further analysis will continue over the coming weeks,” writes the marine park authority in a statement. Experts with the agency note that the single greatest challenge to the reef remains climate change. The organization is continuing to monitor and implement conservation strategies and programs to maintain and promote the health of the reef.