A new study confirms that the 2016 heatwave caused the bleaching and subsequent death of a third of Australia's Great Barrier Reef — a change considered irreversible.
It was the exceptional heatwave recorded in 2016 that caused the bleaching and subsequent death of almost 30 per cent of Australia's Great Barrier Reef. This is confirmed by a new study published in Nature, coordinated by Terry Hughes, director of the Arc Centre of Excellence for Coral Reef Studies, which sought to understand how corals are able to respond to a sudden and prolonged rise in ocean water temperatures. The result is that the majority of corals stretching for 2,300 kilometres off the north-east coast of Australia were unable to withstand the extreme temperatures recorded.
"Corals began to die immediately where the accumulated heat exposure exceeded the critical warming threshold, which turned out to be around 3–4°C per week," the research abstract reads. "After eight months, a rise of 6°C over several weeks led to an unprecedented regional-scale shift in coral composition." A "catastrophe" that is said to have resulted in the death of almost 30 per cent of the 3,863 reefs that make up the Great Barrier Reef, a unique ecosystem in the world.
The study showed that corals did not starve because they were unable to recover their symbionts, as had previously been supposed. Rather, the coral species most sensitive to high temperatures died almost immediately at sites exposed to elevated temperatures. Hughes confirmed to the Guardian that "many millions of corals died rapidly in the northern Great Barrier Reef within just 2–3 weeks."
What we are witnessing, then, is a steady decline that is difficult to halt. So much so that researchers explain that the most likely scenario will be one of continued degradation lasting "until climate change stabilises, allowing the remaining populations to survive and reorganise." The large-scale loss of corals is certainly a precursor to a possible radical transformation of the entire ecosystem, given that this habitat is fundamental to the whole food chain of that part of the ocean — not to mention all the human activities connected to it. The risk of collapse is real, particularly if we fail to limit global warming to 1.5–2°C, as also established by the Paris Agreement.