News Science

Coral Bleaching has Damaged Two-thirds of the Great Barrier Reef

About two-thirds of Australia’s Great Barrier Reef has been damaged by back-to-back years of “severe” coral bleaching, a series of aerial surveys carried out by the team of Australian Research Council’s Centre of Excellence for Coral Reef Studies has revealed.

The 2016 survey of the reef had revealed bleaching to be most severe in the northern third of the Reef, but within one year, the middle third of the reef has been found to have experienced the most severe 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.”

More than 8,000 km (5,000 miles) of the reef area was covered during the aerial surveys in 2017.

Bleaching due to high sea surface temperatures is a catastrophic event for coral reefs. Corals can die as abnormal heat makes them expel their symbiotic algae. Sea surface temperatures are now so high across much of the tropics that many reefs are suffering severe bleaching for consecutive fourth year. Many divers in Australia have already reported new bleaching in the northern part of the Great Barrier Reef. Natural history film-maker Biopixel released a video showing new bleaching on the reef. The Great Barrier Reef Marine Park Authority has also requested visitors to report any signs of bleaching after a second year of unusually high water temperatures.

In 2016, the sea surface temperatures on the Great Barrier Reef were the hottest on record in the months of February, March and April. As a result, the largest ever coral die-off on the Great Barrier Reef was recorded, with almost two-thirds of corals dying in the 700 kilometers north of Port Douglas in far north Queensland.

In February this year, a new study carried out by researchers from the University of Melbourne suggested that the temperatures that caused distressing coral bleaching on the Great Barrier Reef in 2016 could likely become a norm by 2050 unless steps are taken to cut greenhouse gas emissions quickly.

According to Dr. James Kerry, who was also part of the team doing the aerial surveys, “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.”

“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.”

Recently, the Reef and Rainforest Research Centre in Australia and the tourism industry had proposed a $9 million project to save coral bleaching in the Great Barrier Reef by pumping cold water onto a handful of critical reef sites.

The plan has been submitted to the federal government in the country. According to the proponents of this project, this measure could prevent localized bleaching to valuable parts of six reefs near Cairns and Port Douglas.

The plan suggests using low-energy technology to push adjacent cold water from a depth of about 40 meters to the surface to prevent bleaching caused by global warming-induced rises in sea surface temperatures.