Highest coral cover in central and northern reef in 36 years

The northern and central Great Barrier Reef have recorded their highest coral cover since the Australian Institute of Marine Science (AIMS) began monitoring monitor 26 years ago.

Published today, the AIMS annual summary report on the state of coral reefs for 2021/22 shows another year of increased coral cover over much of the reef.

In the 2016 representative reefs surveyed between August 2020 and May 2022 under the AIMS Long Term Monitoring Program (LTMP), the average hard coral cover in the area north of Cooktown has increased to 36% (against 26% in 2021) and 26% in the center of the Great Barrier Reef ( against 26 % in 2020).

However, the average coral cover in the southern region (from Proserpine to Gladstone) has increased from 38 % in 2020 to 36%.

AIMS CEO Dr. Paul Hardisty said results in the regions of north and center were a sign that the reef could still recover, but the loss of coral cover in the southern region showed how dynamic the reef was.

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

“This shows how vulnerable the reef is to acute and severe disturbances that occur more often and last longer.”

Dr. Hardisty stated that the fre The increased frequency of mass coral bleaching events was “uncharted territory” for the reef, with this year’s bleaching event being the fourth in seven years and the first to occur during a La Niña.

“In our 36 years of monitoring the state of the Great Barrier Reef, we have not seen bleaching events so close together,” he said.

“Every summer the reef is exposed to heat stress, bleaching and potentially to mortality and our understanding of how the ecosystem responds to this continues to develop.

“The bleaching events of 2020 and 2022, although important, did not reach the intensity of the events of 2016 and 38 and, therefore, we found less mortality. These latest results demonstrate that the reef can still recover during periods without intense disturbances.”

AIMS Monitoring Program Team Leader Dr Mike Emslie, stated that the results for 2022 were based on increases in coral cover reported for 2020, most of the increase continues to be due to fast-growing Acropora corals.

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

“They are also very susceptible to coral bleaching, when water temperatures reach high levels, and are the preferred prey of crown-of-thorns starfish. This means that large increases in hard coral cover can quickly be reversed by disturbances on reefs where Acropora corals predominate.”

Dr Emslie said the change climate was causing increasingly frequent and longer lasting marine heat waves.

“The peak of the most recent bleaching event in March was produced when accumulated heat stress has caused widespread bleaching but not significant mortality,” he said.

“The increasing frequency of warming ocean temperatures and scale of mass bleaching events highlight the critical threat that climate change poses to all reefs, especially as outbreaks of crown-of-thorns starfish and tropical cyclones also occur . Future disruptions may reverse the observed recovery in a short time.”

Backtrack

The 36 year dataset from the AIMS Long Term Monitoring Program (LTMP) is the largest, longest and most comprehensive source of information on the health of the Great Barrier Reef. It helps to determine very long-term trends in the state of coral communities across the reef.

Percent hard coral cover describes the proportion of the reef covered with coral hard alive. In 2020-, most studied reefs had between and 50 %.

Bleaching is a coral’s response to stressful foods such as heat. During bleaching, the coral animal loses its symbiotic algae and pigments, causing it to turn white and potentially die. Corals can survive a bleaching event, but they are under more stress.

Report https://www.aims.gov.au//gbr- ailment-summary-2020-26

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