[ad_1]
It was a depressing inevitability, if expected, when the Rowley Shoals of Western Australia showed the first signs of mass coral bleaching earlier this year, but a follow-up survey found that a Notable recovery seems 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 that the coral had achieved a “surprising” return to health over the past six months.
“We expected to see widespread mortality, and we just didn’t see it … which is really an amazing thing,” said Dr. Holmes.
The survey was a follow-up to that conducted in April which found that up to 60% of the corals on some Rowley Shoals reefs had bleached after the most widespread sea heatwave since reliable satellite monitoring began. in 1993.
It has long been known that high sea temperatures cause coral bleaching that can kill corals – as seen from the devastation of the Great Barrier Reef off the coast of Queensland – but what is less known is that bleached corals do not they die immediately.
“So when a coral bleaches, it’s really just a sign of initial stress,” said Dr. Holmes.
However, corals rely on these microscopic algae as a food source and cannot survive long without them.
“If that stress continues for a long time and those corals remain white, then it can lead to mortality,” said Dr. Holmes.
“But there are some cases of bleaching around the world where … that stress didn’t continue for very long, and the corals were able to take those algae back out of the water.”
Dr Holmes believes the vital time gap between bleaching and death created a chance for coral reefs to bounce back at Rowley Shoals, a chain of three coral atolls 300 kilometers from Broome on the edge of the Australian continental shelf.
Sea heat wave
Last summer, as bushfires raged on Australia’s east coast, an unprecedented sea heat wave enveloped the west coast, stretching from South Australia to the Kimberley in northern Western Australia.
High seawater temperatures killed crabs, abalone, and other shellfish in the southwest, and killed fish and oysters, and caused widespread coral bleaching in northwest WA.
The Australian Institute of Marine Sciences has partnered with WA’s Department of Biodiversity, Conservation and Attractions to examine the effects of the marine heatwave on offshore coral reefs, including those at Rowley Shoals.
“Based on the original images we were receiving in April, we were really very concerned about the extent of the bleaching.”
Natural protection
The devastating effect of mass bleaching on the Great Barrier Reef is well known, but many people may not be aware of similar catastrophes that have occurred in remote coral reefs off Latin America.
In 2016, scientists documented bleaching of 60-90% of the corals in the Scott and Seringapatam reefs, about 400 kilometers northwest of Broome.
But something different was happening in the Rowley Shoals further south.
“It is one of the few places in WA, and only one of the places in Australia, where we have had long-term stability in coral cover and to date has been largely devoid of large-scale bleaching events.”
Ocean currents off northwestern Australia seemed to be directing increasingly warm summer currents away from the Rowley Shoals, until April of this year.
“This particular event was not foreseen and was a little unusual, but what happened was that the warmer water moved a little further south than we have previously seen it,” said the Dr. Holmes.
But since the change in water currents happened in late summer, unusually warm sea temperatures didn’t wet the Rowley Shoals for long.
“We had this sudden temperature spike, which is when the bleaching occurred,” said Dr. Holmes. “But then the water temperature dropped pretty quickly.”
This would likely reduce the stress on the coral and allow it to recover.
Calm before the long-term storm
The relief that perhaps only 10% of Rowley Shoals coral has been killed, rather than the feared 60%, is mitigated by the knowledge that the worst is almost certain to come.
“We feel like we’ve dodged a bit of a bullet in terms of a widespread bleaching event,” said Dr. Holmes.
James Gilmour, of the Australian Institute of Marine Science, agrees that this time the Rowley Shoals reefs appear to have escaped widespread coral mortality, but fears they may not do as well in the next 10 years.
“With climate change unfolding and ocean warming, we anticipate repeated bleaching events over the next decade, and possibly severe mass bleaching,” said Dr Gilmour.
Documenting the disappearance of Australia’s once pristine coral reefs is the flip side of what at first glance might seem like a dream job for Dr Holmes as he dives at the Rowley Shoals.
“For the tour operators that go out there, for the fishermen who use it, for the scientists who study it, it is quite devastating to see it,” said Dr Holmes.
“If we don’t address the issue of climate change and water warming, then we’re going to have serious problems here.”
.
[ad_2]
Source link
