After a devastating heatwave in 2016 caused the death of half of the Great Barrier Reef in some locations, scientists have had the opportunity to evaluate it and have come to the conclusion the reef is unlikely to recover.
In a report published in Nature, researchers mapped the impact of the 2016 heatwave along the 1429 mile reef. Of the 3,863 reefs that make up the World Heritage site, 29 percent lost two-thirds or more their corals. In the northern region, as much as 50 percent of coral is lost.
The death of the coral comes from bleaching which takes when warmer water temperatures cause corals to expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. When a coral bleaches, it is not dead. Corals can survive a bleaching event, but they are under more stress and are subject to mortality.
The report found that mass bleaching has transformed the reef’s ability to sustain full ecological functioning, and prospects for a full recovery to pre-bleaching levels are “poor” as many coral colonies continue to die. Replacement of fast-growing species can take at least a decade while regrowth for longer-lived, slow-growing coral will “almost certainly” take decades longer.
“The coral die-off has caused radical changes in the mix of coral species on hundreds of individual reefs, where mature and diverse reef communities are being transformed into more degraded systems, with just a few tough species remaining,” said study co-author Professor Andrew Baird in a statement.
The findings serve as an autopsy report into just how bad it really was. In the years spanning 2014-2017, in some areas of the reef temperatures rose as much as 10.8°F (6°C), sometimes lasting as long as eight months. In 2017, the reef again suffered severe stress and bleaching from increased water temperatures.
The findings continue to serve the importance of slowing man-made climate change and the irreversible impact it has on fragile ecosystems that have been around for thousands of years. If global temperatures continue to climb above 3.6°F (2°C) tropical reefs could be “radically altered” and the benefits they provide to hundreds of millions of people could be lost.
The study is part of an IUCN program that aims to classify vulnerable ecosystems as “safe”, “threatened”, or “endangered”, much like the IUCN currently does with animal species. The scientists say their findings reinforce a need to study the risk of wide-scale collapse of reef ecosystems in the face of global climate change.