“We were expecting to see widespread mortality, and we just didn’t see it ….”
It was a depressing, if expected inevitability when Western Australia’s Rowley Shoals showed the first signs of mass coral bleaching earlier this year, but a follow-up survey has found a remarkable recovery looks likely to preserve the reef’s near-pristine health — at least for now.
Tom Holmes, the marine monitoring coordinator at the WA Department of Biodiversity, Conservation and Attractions, said that while his team was still processing the data, it appeared the coral had pulled off an “amazing” return towards health over the past six months.
“We were expecting to see widespread mortality, and we just didn’t see it … which is a really amazing thing,” Dr Holmes said.
The survey was a follow-up to one conducted in April that found as much as 60 per cent of corals on some Rowley Shoals reefs had bleached after the most widespread marine heatwave since reliable satellite monitoring began in 1993.
It has long been known that high sea temperatures cause coral bleaching which can kill coral — as seen by the devastation of the Great Barrier Reef off the Queensland coast — but what is less well known is that bleached corals do not die immediately.
“So when a coral bleaches, it’s actually just a sign of initial stress,” Dr Holmes said.
However, corals rely on these microscopic algae as a food source and cannot survive for long without them.
“If that stress continues for a long time and those corals remain white, then it can lead to mortality,” Dr Holmes said.
“But there are some cases of bleaching around the world where … that stress hasn’t continued for a long time, and the corals have been able to take that algae back in from the water.”
Dr Holmes believes that vital time gap between bleaching and dying created a chance for the reefs to recover at the Rowley Shoals, a chain of three coral atolls 300 kilometres off Broome on the edge of Australia’s continental shelf.