Six months after the extreme underwater heatwave of 2015/2016, many
of the bleached corals have died in the northern third of the Great Barrier Reef.
Scientists are surveying the continuing aftermath of the worst coral bleaching event ever recorded on the Great Barrier Reef. The
large-scale devastation is now being compounded by disease infecting the
damaged corals and by coral predators.
‘Six months after the peak bleaching, the corals now have either regained their algal symbionts and survived, or they have slowly starved to death without the nutrition the algae provide to them.’
Teams of researchers from the ARC Centre of Excellence for Coral
Reef Studies at James Cook University are returning to the same 83 reefs
that they surveyed underwater in March this year at the height of the
"Millions of corals in the north of the Great Barrier Reef died
quickly from heat stress in March and since then, many more have died
more slowly," says Dr. Greg Torda whose team recently returned from
re-surveying reefs near Lizard Island.
The scientists have today released unique footage showing the extent
of the bleaching in March and April, which was most severe in the
northern 700km section of the Great Barrier Reef. Reefs in the southern
half of the reef were only lightly bleached and remain in good
"Six months after the peak bleaching, the corals now have either
regained their algal symbionts and survived, or they have slowly starved
to death without the nutrition the algae provide to them," says Torda.
"On the reefs we surveyed close to Lizard Island, the amount of live
coral covering the reef has fallen from around 40% in March, to under
"In March, we measured a lot of heavily bleached branching corals
that were still alive, but we didn't see many survivors this week," says
Dr Andrew Hoey, who is currently working from Lizard Island Research
"On top of that, snails that eat live coral are congregating on the
survivors, and the weakened corals are more prone to disease. A lot of
the survivors are in poor shape."
"As we expected from the geographic pattern of bleaching, the reefs
further south are in much better shape," says Professor Andrew Baird who
led the re-surveys of reefs in the central section of the Great Barrier
"There is still close to 40% coral cover at most reefs in the
central Great Barrier Reef, and the corals that were moderately bleached
last summer have nearly all regained their normal color."
The final death toll from the bleaching in the north will not be
known until all surveys are completed in mid-November, but it is already
clear that this event was much more severe than the two previous
bleachings in 2002 and 1998.