Great Barrier Reef shows big increase in coral cover, but future uncertain

Parts of Australia’s Great Barrier Reef have recovered strongly in the past year, with the highest levels of coral cover seen in nearly four decades, a government report said on Thursday (Aug 4).

A marine heatwave that hit the reef earlier this year caused bleaching of the corals but not the mass mortality as originally feared, the report by the Australian Institute of Marine Science (AIMS) said.

But while some coral species are thriving, the findings mask the loss of biodiversity on the reef as it faces greater challenges from warmer waters, cyclones and coral-eating starfish.

AIMS’ annual summary report on coral reef condition for 2021/2022 showed increased coral cover across much of the reef. The gains build on increases recorded last year after severe damage from recent marine heatwaves, especially the devastating bleaching events of 2016 and 2017.

This year’s bleaching, when the corals turn white from heat stress, was the fourth such major event in the past seven years.

AIMS said the northern and central reef recorded the highest amount of coral cover since it began monitoring 36 years ago. However, average coral cover in the southern region decreased slightly compared with last year.

Most of the increase was driven by fast-growing Acropora corals, which are vulnerable to wave damage, coral bleaching and crown-of-thorns starfish outbreaks.

AIMS chief executive officer Paul Hardisty said the results in the north and central regions were a sign the reef could still recover, but the loss of coral cover in the southern region also showed how fragile it was.

“A third of the gain in coral cover we recorded in the south in 2020/2021 was lost last year due to ongoing crown-of-thorns starfish outbreaks,” he said in a statement.

Climate change is the largest threat to the reef, which lost half of its coral populations between 1995 and 2017 because of ocean warming, a study published in 2020 found.

Bleaching occurs when sea surface temperatures surpass tolerance levels for the corals. If the high water temperatures last weeks, the corals can die.

But behind the coral cover increase lies a wider problem of loss of species richness across the reef, which has about 600 different types of coral, according to the Great Barrier Reef Marine Park Authority.

“We are already finding evidence that each mass bleaching event leads to local extinctions of rarer species,” said Dr Zoe Richards, senior research fellow from the Coral Conservation and Research Group at Curtin University in Perth.

“So the short-term success of a handful of fast-growing coral species masks the full story about the largely hidden losses of biodiversity on the reef,” she said.

SOURCE: NEWS AGENCIES