Bleak outlook

Left: Map of the Great Barrier Reef showing results of aerial surveys of 911 reefs. Right: coral at Lizard Island Map provided by ARC Centre of Excellence for Coral Reef Studies / Tom Bridge and James Kerry; Coral image at the right provided by Dr Gergely Torda.
20 April 2016

Final results of aerial and underwater surveys reveal that 93% of the Great Barrier Reef (GBR) have been affected by a current bleaching event.

It’s a mixed picture of very severe, moderate and little damage that changes dramatically from north to south along the 2300 kilometres length of the Reef.

According to Professor Terry Hughes, the convenor of the National Coral Bleaching Taskforce, the scale of the bleaching is unprecedented. Of the 911 individual reefs covered by the survey only 7% (68 reefs) were found to have escaped bleaching entirely.

In 316 reefs between 60 and 100% of corals are severely affected. Almost all of these are located in the northern half of the GBR.

Extreme bleaching has occurred in the most remote part of the Reef stretching around 1000 kilometres north of Port Douglas. There the mortality of bleached corals is averaging 50%.

The bleaching in the central section is less severe, and closer to the intensity of the first two mass bleaching events on the GBR, in 1998 and 2002. According to Professor Hughes, most of the corals in this section, which stretches from Mackay to Port Douglas, are expected to survive.

Towards the southern end, most of the reefs have minor to moderate bleaching and are expected to soon recover.

From the three mass bleaching events in 2016, 2002 and 1998, the scientists established that at sites with the most severe bleaching water temperatures are the highest for the longest period of time.

Professor Hughes said that the southern third of the GBR fortunately cooled down late in summer by a period of cloudy weather caused by ex-cyclone Winston. Otherwise the 2016 footprint could have been much worse.

In an expert comment provided by the Australian Science Media Centre, Dr Pat Hutchings from the Australian Museum in Sydney, said:

"We have good data from the Great Barrier Reef showing that localised bleaching events increase rates of reef destruction. If we extrapolate this to entire reefs that are severely bleached, with subsequent death of coral colonies, it presents a conservation risk that cannot be ignored."

Story based on information provided by James Cook University.