Two-thirds of Australia's Great Barrier Reef have been severely damaged by coral bleaching as a result of warming seas, in an event scientists say it will be hard to recover from.
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Coral bleaching occurs when algae living within the coral tissue are expelled, usually as a result of water temperatures being too high. As a result, the coral loses its vibrant appearance and turns white. Still alive, but weakened, coral can recover from such an event if cooling occurs soon enough for algae to embed again.
However, this latest announcement from James Cook University in Australia – which recorded and studied aerial footage of the entire reef in 2016 and 2017, matching 800 individual coral reefs in both surveys – warns that the coral may struggle to recover because current damage is the result of two severe bouts of bleaching occurring in the space of just 12 months. Historically, such severe damage (in this case, impacting 1,500km of reef), has occurred years apart.
“The combined impact of this back-to-back bleaching stretches for 1,500 km (900 miles), leaving only the southern third unscathed,” professor Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies at James Cook University who headed up the aerial surveys, said in a university statement. “The bleaching is caused by record-breaking temperatures driven by global warming. This year, 2017, we are seeing mass bleaching, even without the assistance of El Niño conditions.”
Tropical Cyclone Debbie also hit the reef last month, damaging an area 100km-wide that had been largely undamaged until that time. Despite this, Hughes is adamant that global warming is the main culprit threatening the natural wonder’s survival. He said: “As temperatures continue to rise the corals will experience more and more of these events: 1°C of warming so far has already caused four events in the past 19 years. Ultimately, we need to cut carbon emissions, and the window to do so is rapidly closing.”
Colleague and collaborator James Kerry added that although this is the fourth occasion the reef has been severely damaged since the late 1990s, the fact the reef was pummelled twice in the space of 12 months makes the chances of coral survival slim in the worst-affected spots. “It takes at least a decade for a full recovery of even the fastest growing corals, so mass bleaching events 12 months apart offers zero prospect of recovery for reefs that were damaged in 2016,” he said. The work carried out by Kerry and Hughes has been backed up by in-water studies at every stage, and previous studies have been published in Nature.
Dramatic temperature changes have led to some of the worst coral bleaching in history since the turn of the century. In 2005, a dramatic coral bleaching event led to half the reefs in the Caribbean being severely damaged. Satellite data showed that in one year, the area experienced more thermal stress than the previous 20 years combined. A 2014 report that looked at 35,000 surveys confirmed that more than half the Caribbean’s coral reefs had been lost since the 70s, and that all would disappear within the next two decades unless drastic action is taken.
A 2016 report from the Queensland's Water Science Taskforce estimated that AU$8 billion (£4.7bn) would be needed to save the Great Barrier Reef from total destruction. The Australian government had already committed around AU$40 million to the Reef Trust to address key threats to the reef. “The recommendations set the stage for a bold new era of reform in water quality improvements and that is what we will deliver,” Steven Miles, Queensland’s environment minister, said at the time. This latest report out of James Cook University, suggests far more needs to be done.
This article was originally published by WIRED UK
