Two-thirds of Australia's Great Barrier Reef showed the largest amount of coral cover in 36 years, but the reef remains vulnerable to mass bleaching, an official long-term monitoring programme reported on Thursday Aug 4. The recovery in the central and northern stretches of the UNESCO world heritage-listed reef contrasted with the southern region, where coral cover was lost due to crown-of-thorns starfish outbreaks, the Australian Institute of Marine Sciences AIMS said in its annual report.
This shows how vulnerable the Reef is to the continued acute and severe disturbances that are more often occurring and are longer-lasting, said Paul Hardisty, AIMS Chief Executive Officer.
The report came as UNESCO considers whether to list the Great Barrier Reef as in danger after a visit by UNESCO experts in March. The World Heritage Committee meeting, where the fate of the reef was on the agenda, was due to be held in Russia in June, but was postponed.
In a key measure of reef health, AIMS defines hard coral cover of more than 30 per cent as a high value, based on its long-term surveys of the reef.
In the northern region, the average hard coral cover increased to 36 per cent in 2022 from a low of 13 per cent in 2017, while the central region hard coral cover increased to 33 per cent from a low of 12 per cent in 2019 - the highest levels recorded for both regions since the institute began monitoring the reef in 1985.
Coverage fell to 34 per cent in the southern region, which generally has higher hard coral cover than the other two regions, from 38 per cent a year earlier in the year.
The recovery comes after the fourth mass bleaching in seven years and the first mass bleaching during a La Nina event, but Hardisty said that the bleaching in 2020 and 2022 was not as damaging as in 2016 and 2017 and that in 2020 and 2022 was not as damaging as in 2016 and 2017.
Hardisty said that the Reef can recover in periods without intense disturbances because of these latest results.
On the downside, the growth in cover has been driven by Acropora corals, which AIMS said are particularly vulnerable to wave damage, heat stress and crown-of-thorns starfish.
Large increases in hard coral cover can be negated quickly by disturbances on reefs where Acropora corals predominate, AIMS monitoring programme leader Mike Emslie said.