The central and northern stretches of Australia's Great Barrier Reef are showing the highest coral cover seen in 36 years, showing that the fragile UNESCO World Heritage site could still recover from, a monitoring group reported Thursday. Coral cover in the southern region of the reef decreased, however, and the reef is vulnerable to increasingly common disturbances like mass bleaching events, the group said.
There was an increase in average hard coral cover in the northern region of the reef to 36% in 2022 from 27% in 2021, and an increase in in the central region to 33% in 2022 from 27% in 2021, the Australian Institute of Marine Sciences (AIMS) said in its annual summary report.
Despite this, "a third of the gain in coral cover we recorded in the south in 2020/21 was lost last year due to ongoing crown-of-thorns starfish outbreaks," Dr. Paul Hardisty, CEO of AIMS, said in a statement. "This shows how vulnerable the Reef is to the continued acute and severe disturbances that are occurring more often, and are longer-lasting."
AIMS has been monitoring the Great Barrier Reef since 1986. It said the increase in frequency of mass bleaching events — when coral, in response to stressful conditions like heat, loses its pigments and symbiotic algae, turns white, and potentially dies — were "uncharted territory."
"In our 36 years of monitoring the condition of the Great Barrier Reef we have not seen bleaching events so close together," Hardisty said. "Every summer the Reef is at risk of temperature stress, bleaching and potentially mortality and our understanding of how the ecosystem responds to that is still developing."
Dr. Mike Emslie, also from the AIMS monitoring program, said that most of the coral increase in the north and central parts of the reef was driven by fast-growing but fragile Acropora corals, and could therefore be reversed quickly.
"These corals are particularly vulnerable to wave damage, like that generated by strong winds and tropical cyclones," Emslie said. "The increasing frequency of warming ocean temperatures and the extent of mass bleaching events highlights the critical threat climate change poses to all reefs, particularly while crown-of-thorns starfish outbreaks and tropical cyclones are also occurring. Future disturbance can reverse the observed recovery in a short amount of time."