Highest coral cover in the central and northern Great Barrier Reef since monitoring began 36 years ago

This year, the northern and central Great Barrier Reef has seen the highest amount of coral cover since the Australian Institute of Marine Sciences (AIMS) began monitoring 36 years ago.

Posted recently, AIMS Annual Summary Report on the State of Coral Reefs 2021/2022. shows another year of increased coral cover over much of the reef.

In 87 representative reefs surveyed from August 2021 to May 2022 under AIMS Long Term Monitoring Program (LTMP)average hard coral cover in the region north of Cooktown, Queensland, Australia increased to 36% (from 27% in 2021) and to 33% in the central Great Barrier Reef (from 26% in 2021).

However, the average coral cover in the southern region (from Proserpine to Gladstone) decreased from 38% in 2021 to 34%.

AIMS Director General Dr Paul Hardisty said the results in the northern and central regions suggested the Reef could recover, but the loss of coral cover in the southern region showed how dynamic the Reef had been.

“A third of the coral cover growth we recorded in the south in 2020/21 was lost last year due to sustained outbreaks of crown-of-thorns starfish,” he said.

“This shows how vulnerable the reef is to sustained, acute and severe disturbances that occur more frequently and continue.”

Dr Hardisty said the increasing frequency of mass coral bleaching was “uncharted territory” for the Reef, with this year’s bleaching the fourth in seven years and the first to occur during La Niña.

“In 36 years of monitoring the condition of the Great Barrier Reef, we have never seen bleaching so close together,” he said.

“Each summer the Reef is at risk of temperature stress, bleaching and potential mortality, and our understanding of how the ecosystem responds is still evolving.

“The bleaching events in 2020 and 2022, although extensive, did not reach the intensity of the 2016 and 2017 events, and as a result we saw less mortality. These latest results demonstrate that the Reef can still recover during periods without intense disturbance.”

AIMS monitoring program manager Dr Mike Emslie said the 2022 results were based on the increase in coral cover reported for 2021. Acropora necklaces

“These corals are particularly vulnerable to wave damage, such as that created by strong winds and tropical cyclones,” he said.

“They are also very susceptible to coral bleaching when water temperatures reach elevated levels and are preferred prey for crown-of-thorns starfish. This means that significant increases in hard coral cover can be quickly nullified by reef disturbances Acropora corals predominate.”

Dr Emslie said climate change was causing more frequent and longer-lasting marine heat waves.

“The peak of the last bleaching event in March occurred when accumulated heat stress caused widespread bleaching but not much mortality,” he said.

“The increased frequency of ocean warming and the scale of mass bleaching highlights the critical threat climate change poses to all reefs, especially when crown-of-thorns starfish outbreaks and tropical cyclones also occur. Future disruptions could reverse the observed recovery in a short period of time.”

Background

The 36-year AIMS Long-Term Monitoring Program (LTMP) dataset is the largest, longest-running and most comprehensive source of information on the condition of the Great Barrier Reef. This helps identify long-term trends in the condition of coral communities on the reef.

Percent hard coral cover describes the proportion of a reef covered by living hard corals. In 2021-2022, most reefs surveyed had between 10 and 50 percent.

Bleaching is a response of corals to stressful conditions such as heat. During bleaching, coral animals lose their symbiotic algae and pigments, turning white and potentially dying. Although corals can survive bleaching, they are under more stress.