New report on Great Barrier Reef shows coral cover increases before onset of serious bleaching, cyclones
Coral cover has increased in all three regions on the Great Barrier Reef and is at regional highs in two of the three regions according to a report by the Australian Institute of Marine Science (AIMS). But the results come with a note of caution
Australian Institute of Marine Science
Most of the underwater surveys contributing to these findings, published today, were conducted before and during the recent mass bleaching event, one of the most extensive and serious on record, and have not yet captured how many corals survived or died following the bleaching.
Surveys in the Central region were also completed before the passage of tropical Cyclone Jasper in December 2023.
AIMS’ Long-Term Monitoring Program (LTMP) leader Dr Mike Emslie said coral cover increases were a positive sign but did not reflect the potentially destructive consequences of the 2024 mass bleaching event.
“We saw evidence of early onset mortality, particularly in the Southern region, but the full picture of mortality was not yet apparent during this year’s surveys,” he said.
“While bleached corals are very stressed, they are still alive and are recorded as live coral on our surveys.
“Some types of corals can remain bleached for months, remaining on a knife edge between survival and death. This is why returning and repeating surveys of the reefs in this vast, complex and dynamic system is so important. This year’s results serve as a very important reference against which to measure the impacts of the summer’s events.”
The next (LTMP) survey season recommences in September and will capture impacts on coral cover from this summer’s mass bleaching event and the cyclones, with a full assessment complete by mid-2025.
“Climate change remains the greatest threat to the Reef because it drives these mass bleaching events. This most recent one was the fifth such event since 2016. These more frequent and extensive marine heatwaves will lead to shortened ‘windows’ for coral recovery. Recent gains, while encouraging, can be lost in a short amount of time,” Dr Emslie said.
Surveys were conducted at 94 Reefs spread through the Northern, Central and Southern Great Barrier Reef between August 2023 and June 2024.
The Report recorded the following average hard coral coverage:
- Northern region (north of Cooktown) – 39.5%, up from 35.8% last year;
- Central region (Cooktown to Proserpine) – 34%, up from 30.7%;
- Southern region (south of Proserpine) – 39.1%, up from 34%.
The AIMS report finds that small rises in coral cover this year bring the Northern and Central regions to their highest levels in 38 years of monitoring.
The surveys also found that crown-of-thorns starfish outbreaks have persisted on some reefs in the Southern region.
The long term monitoring team surveyed reefs off Townsville after the passage of tropical Cyclone Kirrily in late January, finding evidence of storm damage and declines in hard coral cover ranging from 6% to 10% at Kelso, John Brewer, Helix and Chicken Reefs. Other reefs appear to have escaped with little impact.
AIMS Research Program Director Dr David Wachenfeld said the regional increases in coral cover are encouraging, showing the Reef’s capacity for recovery after reaching their lowest levels within the last 15 years. However, climate change and other disturbances mean this recovery is fragile and Reef resilience is not limitless.
“In many ways the Reef has had some lucky escapes in recent years. The 2020 and 2022 mass bleaching events had levels of heat stress that were not as intense as the 2016 and 2017 events or the 2024 event. Coupled with very few other events causing widespread coral death, that has led to the levels of coral cover increase we have seen,” he said.
“But the frequency and intensity of bleaching events is unprecedented, and that is only forecast to escalate under climate change, alongside the persistent threat of crown-of-thorns starfish outbreaks and tropical cyclones”.
Aerial surveys undertaken by AIMS and the Great Barrier Reef Marine Park Authority in February and March found bleached corals in the shallows of 73% of reefs surveyed across all three regions.
In recent weeks, AIMS scientists in separate monitoring programs observed substantial mortality in reefs that were particularly hard hit by the 2024 event.
“We are only one large scale disturbance event away from a reversal of the recent recovery. The 2024 bleaching event could be that event – almost half of the 3000 or so reefs that make up the marine park experienced more heat stress than ever recorded,” Dr Wachenfeld said.
“We still don’t know how much mortality this event has caused. Our monitoring over the next 12 months will help us to understand how this bleaching event stacks up against the others in the last decade.”
AIMS CEO Professor Selina Stead said AIMS was prioritising research to develop scientific solutions to boost reef resilience under a warming climate.
“Climate change is increasing pressure on reef systems around the world,” she said. “The 2024 bleaching event was part of the fourth global bleaching event, announced in April.
“These vitally important ecosystems that millions rely upon need strong greenhouse gas emissions reduction, science-based management of local pressures, and input from multiple fields of research if they are to endure.
“At AIMS we are developing a toolbox of interventions to help reefs adapt to and recover from the effects of climate change.”
Background
The LTMP quantifies long term trends in the status of coral communities across the Great Barrier Reef.
Researchers use hard coral cover as one indicator of the condition of each reef. Percentage hard coral cover is estimated by trained scientists during manta tow surveys and is a metric which allows AIMS scientists to provide an overview of the Great Barrier Reef’s status and keep policy makers, managers and other scientists informed in a timely manner.
The LTMP also does more detailed surveys on fixed sites on 71 reefs across the Great Barrier Reef. The detailed information includes what types of corals and species of fish are present, their abundance, and causes of mortality like crown-of-thorns starfish numbers, coral disease and bleaching observations.
The LTMP contributes to the Reef 2050 Integrated Monitoring and Reporting Program. Learn more about the LTMP and access detailed data displays at the level of individual reefs or regions.
Download images and vision here.
Method of Research
Data/statistical analysis
Subject of Research
Animals
Long-term coral reef monitoring continues to deliver crucial insights
As the effects of a changing climate and other ecological insults compound, many coral reefs face severe perturbations and a generally poor prognosis for recovery. In an article published in BioScience's new "Perspective and Insight" category, Dr. Peter J. Edmunds of California State University, Northridge, argues for the continued monitoring of coral reefs, even when the seascapes they inhabit are in a significantly degraded state.
Drawing from his ongoing 37-year study in the US Virgin Islands, Edmunds argues that "only consistent, rigorous, and detail-oriented monitoring can document the losses of coral that already have taken place and provide constrained glimpses of the benthic communities that will dominate shallow, tropical marine habitats in the future." Dr. Edmunds's research relies heavily on photoquadrats—one-by-one meter underwater photographs taken at fixed locations over time. These images provide a consistent, quantifiable record of changes in coral cover and community composition, allowing researchers to track the health reef communities in great detail.
Edmunds' monitoring has revealed unexpected resilience in some cases, alongside devastating losses in others, as well as other ecological surprises that challenge our understanding of reef dynamics. For example, two major hurricanes in 2017 had less impact on coral cover than a single hurricane in 1989—likely because chronic disturbances had resulted in a more hurricane-resilient low-cover state, says Edmunds. He continues, stating that long-term monitoring "supports an objective test of the role of acute versus chronic disturbances in driving changes on the reefs."
In concluding, Edmunds argues for the great value of ongoing monitoring, both for conservation purposes and to provide a greater understanding of underlying ecological processes: "Monitoring remains the essential tool through which there is any hope of keeping up with detecting the fast pace of changes affecting the natural world in the twenty-first century."
Journal
BioScience
Method of Research
Experimental study
Subject of Research
Animals
Article Title
Why keep monitoring coral reefs?
Article Publication Date
9-Aug-2024
New 400-year temperature record shows Great Barrier Reef is facing catastrophic damage, researchers warn
Sea surface temperatures have reached critical levels for mass coral bleaching
video:
Removing a skeletal core from a coral colony in the Coral Sea
view moreCredit: Tom DeCarlo, Tulane University
The Great Barrier Reef is under critical pressure, with warming sea temperatures and mass coral bleaching events threatening to destroy the remarkable ecology, biodiversity, and beauty of the world’s largest coral reef, according to new research published today.
‘Highest ocean heat in four centuries places Great Barrier Reef in danger’, published in Nature (8 August), led by University of Wollongong (UOW) Honorary Fellow and University of Melbourne Lecturer Dr Benjamin Henley, provides new evidence of the impact that rising sea surface temperatures have had, and will continue to have, on Australia’s ecological jewel.
Last week, UNESCO’s World Heritage Committee handed down its final decision on the state of the Great Barrier Reef, declining to list the Reef as in danger. However, the scientists have pushed back and say, based on their new evidence, the Great Barrier Reef is absolutely in danger.
Dr Henley and his team combined sea surface temperature reconstructions using geochemical data from coral cores previously collected from the region. They also analysed climate model simulations of sea surface temperatures run with and without climate change, finding that human-caused climate change is to blame for the rising temperatures in the region.
The recent mass bleaching events coincide with five of the six hottest years in the new 400-year-long record. In the years 2024, 2017 and 2020, the Coral Sea reached 400-year highs, with 2024 being the warmest on record by a large margin. The recent heat events in 2016, 2004, and 2022, were the next warmest three years on record. The impact on the Great Barrier Reef’s unparalleled ecology and biodiversity over repeated sequences of mass coral bleaching is devastating.
“When I plotted the 2024 data point, I had to triple check my calculations – it was off the charts – far above the previous record high in 2017. I could almost not believe it. Tragically, mass coral bleaching has occurred yet again this year,” Dr Henley said.
“In the absence of rapid, coordinated and ambitious global action to combat climate change, we will likely witness the demise of one of Earth’s most spectacular natural wonders.
“When you compile all of the evidence we have, it’s the inevitability of the impacts on the reef in the coming years that really gets to me.”
Professor Helen McGregor, from UOW’s Environmental Futures, who is the second author of the study, said urgent action is needed to prevent devastation of one of the world’s most important ecosystems.
“There is no ‘if, but or maybe’—the ocean temperatures during these bleaching events are unprecedented in the past four centuries.
“The Great Barrier Reef is facing catastrophe if anthropogenic climate change is not immediately addressed. The very corals that have lived for hundreds of years and that gave us the data for our study are themselves under serious threat,” Professor McGregor said.
“Our climate model analysis confirms that human influence on the climate system is responsible for the rapid warming in recent decades,” said Dr Henley, who undertook most of the study as a post-doctoral researcher at UOW, where he is now an Honorary Fellow.
“Without urgent intervention, our iconic Great Barrier Reef is at risk of near-annual bleaching from high ocean temperatures. The Reef’s fundamental ecological integrity and outstanding universal value are at stake.
“We have many of the key solutions to stop climate change; what we need is a step change in the level of coordinated national and international action to transition to net zero.
“We can never lose hope. Every fraction of a degree of warming we avoid will lead to a better future for the human and natural systems of our planet.
“We hope that our study equips policymakers with more evidence to pursue deeper cuts in greenhouse gas emissions internationally.”
Coral bleaching occurs when stress causes the corals to expel the algae that live in their tissue. The algae give corals their vibrant colours and without them the coral’s white skeleton is exposed. Stress from environmental disturbances and declining water quality can lead to bleaching, but recent warming in sea temperatures has led to bleaching on a mass scale. Corals can recover from bleaching events if the stress trigger, such as extreme ocean warming, is reduced for a significant period. The reef has experienced five major mass coral bleaching events since 2016.
While the Great Barrier Reef is the world’s largest coral reef system, the groundbreaking research has implications for coral reef systems throughout the world, highlighting the link between the long-term trajectory of extreme ocean temperatures and the ecological health and biodiversity of these complex and crucial ecosystems.
Researchers from Securing Antarctic’s Environmental Future, UOW, University of Melbourne, The University of Queensland, the Australian Institute of Marine Science, Tulane University (USA), and Columbia University (USA) contributed to the paper.
UOW is committed to addressing the United Nations Sustainable Development Goals, which provide a shared blueprint to achieve a better and more sustainable future for everyone. These projects address Goal 13, Climate Action; and Goal 14, Life Below Water.
‘Highest ocean heat in four centuries places Great Barrier Reef in danger’ is published in Nature. https://www.nature.com/articles/s41586-024-07672-x
Journal
Nature
Subject of Research
Animals
Article Title
Highest ocean heat in four centuries places Great Barrier Reef in danger
Article Publication Date
7-Aug-2024
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