Two-thirds of Great Barrier Reef hit by back-to-back mass coral bleaching

For the second time in just 12 months, scientists have recorded severe coral bleaching across huge tracts of the Great Barrier Reef after completing aerial surveys along its entire length. In 2016, bleaching was most severe in the northern third of the Reef, while one year on, the middle third has experienced the most intense coral bleaching.

“The combined impact of this back-to-back bleaching stretches for 1,500 km (900 miles), leaving only the southern third unscathed,” says Prof. Terry Hughes, Director of the ARC Centre of Excellence for Coral Reef Studies, who undertook the aerial surveys in both 2016 and 2017.

“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.”

The aerial surveys in 2017 covered more than 8,000 km (5,000 miles) and scored nearly 800 individual coral reefs closely matching the aerial surveys in 2016 that were carried out by the same two observers.

Dr. James Kerry, who also undertook the aerial surveys, explains further, “this is the fourth time the Great Barrier Reef has bleached severely – in 1998, 2002, 2016, and now in 2017. Bleached corals are not necessarily dead corals, but in the severe central region we anticipate high levels of coral loss.”

“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.”

Coupled with the 2017 mass bleaching event, Tropical Cyclone Debbie struck a corridor of the Great Barrier Reef at the end of March. The intense, slow-moving system was likely to have caused varying levels of damage along a path up to 100 km in width. Any cooling effects related to the cyclone are likely to be negligible in relation to the damage it caused, which unfortunately struck a section of the reef that had largely escaped the worst of the bleaching.

“Clearly the reef is struggling with multiple impacts,” explains Prof. Hughes. “Without a doubt the most pressing of these is global warming. 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.”

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MULTIMEDIA: A selection of photos and videos and key graphic (see below) *Images must carry credits as listed in Dropbox folder*

Key graphic 2016 -2017_GBRbleaching.jpg (high and low res versions available)

This composite map shows surveyed coral reefs in 2016 (left panel) and 2017 (right panel).

Not all data is shown, only reefs at either end of the bleaching spectrum: Red circles indicate reefs undergoing most severe bleaching (60% or more of visible corals bleaching) Green circles indicate reefs with no or only minimal bleaching (10% or less of corals bleaching).

CONTACTS:

Prof. Terry Hughes
Director, ARC Centre of Excellence for Coral Reef Studies
Phone: +61 (0)400 720 164, +61 (0)7 4781 4000
Email: Terry.Hughes@jcu.edu.au

Dr. James Kerry
Senior Research Officer, ARC Centre of Excellence for Coral Reef Studies
Phone: +61 (0)407 475 576, +61 (0)7 4781 4823
Email: james.kerry1@jcu.edu.au

Prof. Sean Connolly
Chief Investigator, ARC Centre of Excellence for Coral Reef Studies
Phone: +61 (0)7 4781 4242
Email: sean.connolly@jcu.edu.au

Melissa Lyne
Communications Manager, ARC Centre of Excellence for Coral Reef Studies
Phone: +61 (0)415 514 328
Email: Melissa.lyne@jcu.edu.au

Note for editors

The two observers: Prof Terry Hughes and Dr. James Kerry work at the ARC Centre of Excellence for Coral Reef Studies at James Cook University in Townsville, Australia. The Centre for World University Rankings recently ranked this institution number 1 globally for Marine and Freshwater biology research.

The aerial survey techniques used in this study were employed consistently in all four bleaching events on the Great Barrier Reef: 1998, 2002, 2016 and 2017. They were backed up by extensive in-water research during the 2016 event and published in the peer-reviewed journal, Nature. (Link to journal)

Coral bleaching occurs when abnormal environmental conditions, like heightened sea temperatures, cause corals to expel tiny photosynthetic algae, called ‘zooxanthellae’. The loss of these colorful algae causes the corals to turn white, and bleach͛. Bleached corals can recover if the temperature drops and zooxanthellae are able to recolonise them, otherwise the coral may die.

In the six months following the peak of bleaching in March 2016, scientists measured on average 67% loss of corals in the northern 700 km section of the Great Barrier Reef, which was the worst impacted section in that year. An interactive map of images and video of aerial survey footage from the 2016 event can be found here.