Global coral bleaching over the last two years has led to widespread coral decline and habitat loss on the Great Barrier Reef.
Since December 2015, the Great Barrier Reef has been exposed to above average sea surface temperatures, due to the combined effects of climate change and a strong El Niño.
These conditions triggered mass coral bleaching in late summer 2016 and led to an estimated 29 per cent loss of shallow water coral Reef-wide, according to findings by the Great Barrier Reef Marine Park Authority.
Winter sea surface temperatures in 2016 remained above average and, by the beginning of the 2016-17 summer, the accumulated heat stress on the Reef resulted in a second wave of mass bleaching.
Staff from the Marine Park Authority took part in aerial surveys conducted by the ARC Centre of Excellence for Coral Reef Studies, and the results confirmed the extent and severity of the 2017 bleaching event.
As seen last year, bleaching and mortality can be highly variable across the 344,400 square kilometre Marine Park — an area bigger than Italy. The Centre of Excellence’s maps below show the 2017 bleaching footprint differs from 2016 in that it extends further south in the Marine Park.
In-water surveys and other reports from the community and our science and tourism partners have also been used to determine the health of the Reef following these events.
In addition to severe bleaching affecting over half the Reef since 2016, large portions of the Reef have also been subjected to other simultaneous impacts during the 2016-17 summer.
Severe tropical cyclone Debbie crossed the coast at Airlie Beach on 28 March 2017.
It is estimated approximately 28 per cent of the total reef area in the Marine Park was within the ‘catastrophic damage zone’ of the cyclone’s path.
Surveys conducted by the Great Barrier Reef Marine Park Authority and Queensland Parks and Wildlife Service have revealed that some sites have suffered significant damage (up to 97 percent coral loss) and are down to very low coral cover, while others received less damage and still have moderate coral cover.
Studies following previous extreme weather events revealed that even within severely damaged reefs, there were often areas that were relatively undamaged. These areas are critical for providing the next generation of corals and assisting with reef recovery..
On becoming an ex-tropical cyclone, the system brought torrential rain to parts of the central and southern Great Barrier Reef catchment, which caused flooding of the Burdekin and Fitzroy Rivers, and resultant flood plumes.
Outbreaks of coral disease and crown-of-thorns starfish have also been ongoing.
The cumulative impact of these disturbances are affecting most of the Great Barrier Reef Marine Park (see graphic), and it is likely the resilience of the majority of reefs north of Mackay has been severely diminished.