Global coral bleaching over the last two years has led to widespread coral decline and habitat loss on the Great Barrier Reef.
Great Barrier Reef Marine Park Authority Chairman Russell Reichelt said ongoing and future climate impacts were concerning.
“As has been the case with reefs across the world, the Great Barrier Reef has experienced significant and widespread impacts over the last two years,” he said.
“We’re very concerned about what this means for the Great Barrier Reef itself and what it means for the communities and industries that depend on it.
“The amount of coral that died from bleaching in 2016 is up from our original estimates and, at this stage, although reports are still being finalised, it’s expected we’ll also see an overall further coral cover decline by the end of 2017.”
Throughout 2016 the Marine Park Authority, Queensland Parks and Wildlife Service, Australian Institute of Marine Science (AIMS) and the ARC Centre of Excellence for Coral Reef Studies conducted extensive surveys of the mass bleaching.
Both aerial and in-water surveys confirmed a pronounced gradation in impacts from north to south.
The most severe mortality was confined to the area north of Port Douglas, where an estimated 70 per cent of shallow water corals died and there was significant variability between and within reefs.
It’s now confirmed an estimated 29 per cent of shallow water corals died from bleaching in 2016. Coral bleaching did extend to deeper corals beyond depths divers typically survey to, but mortality cannot be systematically assessed.
This up from the original estimated 22 per cent in mid-2016, with most mortality occurring in the north of the Reef.
Over this same period there continued to be strong recovery in the south in the absence of bleaching and other impacts.
In 2017, further coral loss is expected from the second consecutive year of bleaching and the impacts of tropical cyclone Debbie.
This is in addition to ongoing impacts from crown-of-thorns starfish, coral disease and poor water quality from coastal run-off.
The 2017 pattern of bleaching was similar to 2016, but most severe in the centre of the Reef between Cairns and Townsville. Ongoing thermal stress is also causing elevated coral disease.
Tropical cyclone Debbie impacted around a quarter of the Reef in early 2017.
Impacts from cyclones are generally patchy, but due to its category four intensity and slow speed as it crossed the reef, coral mortality is expected to be high in this zone, which includes the Whitsunday Islands tourism area.
A complete picture for 2017 won’t be available until early next year. Ongoing bleaching, tropical cyclone Debbie, crown-of-thorns starfish and coral disease are all having impacts.
AIMS has been tracking coral cover in the Great Barrier Reef since 1985, providing a holistic picture over time of net coral cover (including both coral loss from impacts and coral growth from recovery).
While varying from year-to-year, the AIMS data shows a declining trend in coral cover since 1985.
Cyclones and coral-eating crown-of-thorns starfish were responsible for the greatest coral loss before 2016.
Combined with coral bleaching — which is predicted to become more frequent and more severe as a result of steadily rising ocean temperature — the long-term trend of coral decline is expected to continue and accelerate. Recovery from bleaching is also likely to be slower than from other impacts.