ALMOST one-third of reefs in the Great Barrier Reef were damaged worse than previously thought due to high water temperatures off the east coast of Australia in 2016, according to a new study released Thursday.
The study, published in the journal Nature, found severe bleaching on an unprecedented scale triggered mass death of corals. This drastically changed the species composition of almost one-third of the 3,863 individual reefs that comprise the Great Barrier Reef.
“When corals bleach from a heatwave, they can either survive and regain their colour slowly as the temperature drops, or they can die,” Terry Hughes, lead study author and director of the Australian Research Council Centre of Excellence for Coral Reef Studies, said in a statement.
Bleaching occurs when heat kills or expels algae that have a symbiotic relationship with reef-building corals. Without the algae there to provide energy and nutrients, the corals often die.
— Terry Hughes (@ProfTerryHughes) April 19, 2016
The UNESCO World Heritage Site, at 2,300 kilometres long, is the longest and largest coral reef in the world. While the heatwave of 2016, was reported at the time, it is only now that scientists are truly beginning to understand just how catastrophic it was.
But Hughes believes the worst damage was not down to bleaching but the heat alone.
“They cooked because the temperatures were so extreme,” he told ABC, referring to temperature-sensitive species of corals which began to die almost immediately when water temperatures rose. Especially those in the northern reaches of the reef that died from heat stress.
“The study paints a bleak picture of the sheer extent of coral loss on the Great Barrier Reef,” says Nick Graham, a marine ecologist at Lancaster University, UK.
But this goes far beyond just Australia. Approximately one-third of the world’s coral reefs were affected by bleaching in 2016, the study suggests. During this time, less than 10 percent of reefs on the Great Barrier Reef escaped with no bleaching, compared with more than 40 percent in previous bleaching events.
New study shows climate change-associated heat in 2016 transforming GBR: https://t.co/i1S8JipSzd. Unfortunately even under #ParisAgreement 2016-like heat will be more common https://t.co/fjxcuYYgBo pic.twitter.com/9zRM0glSMJ
— Andrew King (@AndrewKingClim) April 19, 2018
The fate of tropical coral reefs – including the iconic Great Barrier Reef – therefore depends on efforts to mitigate climate change, says Graham.
“A future with coral reefs, their rich diversity and the livelihoods they provide to people is quite simple. It will only be possible if carbon emissions are rapidly reduced.”