Warming bleaches reef again
BACK-to-back bleaching is killing huge tracts of the Great Barrier Reef, with almost none of the coral affected in 2016 expected to recover.
Recent aerial surveys by the Australian Research Council's Centre of Excellence for Coral Reef Studies have revealed only the southern third of the reef is unscathed from the bleaching events.
Researcher Terry Hughes said mass bleaching happened this year even without the assistance of El Nino, which normally brought warmer sea surface temperatures.
"The bleaching is caused by record-breaking temperatures driven by global warming,” Professor Hughes said.
"Ultimately, we need to cut carbon emissions, and the window to do so is rapidly closing.”
Warmer water tempera- tures cause coral to expel their algae, sometimes turning them fluorescent and eventually bone white.
Marine biologist James Kerry said bleached corals were not necessarily dead yet but it was anticipated high levels would be lost in the central region of the reef that had the most intense bleaching this year.
"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,” Dr Kerry said.
Tropical Cyclone Debbie also destroyed parts of the reef around the Whitsundays - a popular tourist destination that had largely escaped the worst of the bleaching.
While cyclones normally caused the water temperature to drop, Prof Hughes said any cooling effects were likely to be negligible in relation to the damage caused by Debbie.
"Clearly the reef is struggling with multiple impacts,” he said.
The Great Barrier Reef is known to have had four bleaching events in the past 20 years as the planet warmed by about 0.3 degrees - in 1998, 2002, 2016 and 2017.