Reef ravaged by rare heatwave
A rare underwater heatwave has killed a large portion of the Great Barrier Reef, the world’s largest living structure.
Scientific research conducted underwater and from the air since March has found that swathes of the reef’s northeastern section have been destroyed.
Greg Torda, a zoologist at James Cook University in Queensland, said: ‘‘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 slowly.’’
The heatwave was caused by El Nino, the climate cycle that has raised the temperature of the Pacific Ocean.
The March spell caused mass bleaching across the corals of the 2200-kilometre reef.
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 slowly. Greg Torda, zoologist, James Cook University
Bleaching happens when the coral suffers from environmental stress. The coral then expels the algae that live in it and feed it, leaving the white skeleton visible.
Bleached coral can stay alive but, deprived of its main food source, it begins to starve. The coral’s immune system and defences then break down against the underwater snails that feed on it.
The findings, published by The Conversation website, have alarmed environmentalists, but the damage is not at an end. It is estimated that much of a 650km section above Port Douglas has been destroyed.
James Cook University scientists also examined coral near Lizard Island, 1600km north of Brisbane.
They found that before March, 40 per cent of the reef in that area was alive, but after the heatwave, only 5 per cent had survived. Even the small amount of coral still alive was threatened.
Andrew Baird, a professor at the university, said: ‘‘On top of that, snails that eat live coral are congregating on the survivors. A lot of survivors are in poor shape.’’
Baird said there was only a slim chance that the northern third of the Great Barrier Reef could survive, but it would depend on the health of the southern sections.
‘‘There’s still a lot of reef here, which could [help] the reef up north to recover,’’ he said.
‘‘But it’s likely to take a very long time because the scale of the event around Lizard Island and further north was so large.’’
Baird said most of the reefs surveyed further south were in reasonably good condition.
‘‘That’s a positive,’’ he said. ‘‘But with the current trajectories of carbon dioxide and ocean temperatures, there’s nothing to say that those areas might not bleach as soon as next year.’’