The Great Barrier Reef has lost half of its coral in the last 27 years

Can we save the Reef by controlling crown of thorns starfish?

The Great Barrier Reef has lost half its coral cover in the last 27 years. The loss was due to storm damage (48%), crown of thorns starfish (42%), and bleaching (10%) according to a new study published in the Proceedings of the National Academy of Sciences today by researchers from the Australian Institute of Marine Science (AIMS) in Townsville and the University of Wollongong.

“We can’t stop the storms but, perhaps we can stop the starfish. If we can, then the Reef will have more opportunity to adapt to the challenges of rising sea temperatures and ocean acidification, says John Gunn, CEO of AIMS.

“This finding is based on the most comprehensive reef monitoring program in the world. The program started broadscale surveillance of more than 100 reefs in 1985 and from 1993 it has incorporated more detailed annual surveys of 47 reefs,” says one of the program’s original creators, Dr Peter Doherty, Research Fellow at AIMS.

“Our researchers have spent more than 2,700 days at sea and we’ve invested in the order of $50 million in this monitoring program,” he says.

“The study shows the Reef has lost more than half its coral cover in 27 years. If the trend continued coral cover could halve again by 2022. Interestingly, the pattern of decline varies among regions. In the northern Great Barrier Reef coral cover has remained relatively stable, whereas in the southern regions we see the most dramatic loss of coral, particularly over the last decade when storms have devastated many reefs. ” says Peter Doherty.

The study clearly shows that three factors are overwhelmingly responsible for this loss of coral cover. Intense tropical cyclones have caused massive damage, primarily to reefs in the central and southern parts of the Reef, while population explosions of the coral-consuming Crown-of-thorns starfish have affected coral populations along the length of the Reef. Two severe coral bleaching events have also had major detrimental impacts in northern and central parts of the GBR.

“Our data show that the reefs can regain their coral cover after such disturbances, but recovery takes 10-20 years. At present, the intervals between the disturbances are generally too short for full recovery and that’s causing the long-term losses,” says Dr Hugh Sweatman, one of the study’s authors.

“We can’t stop the storms, and ocean warming (the primary cause of coral bleaching) is one of the critical impacts of the global climate change,” says AIMS CEO, John Gunn. ”However, we can act to reduce the impact of crown of thorns,” he says. “The study shows that in the absence of crown of thorns, coral cover would increase at 0.89% per year, so even with losses due to cyclones and bleaching there should be slow recovery.

“We at AIMS will be redoubling our efforts to understand the life cycle of crown of thorns so we can better predict and reduce the periodic population explosions of crown of thorns. It’s already clear that one important factor is water quality, and we plan to explore options for more direct intervention on this native pest.”

Media contacts

Steve Clarke, AIMS Communication Manager, 07 4753 4264; 0419 668 497;
Niall Byrne, Science in Public, 0417 131 977,

Background information including the paper, fact sheets on the study, the Great Barrier Reef and Crown-of-thorns; photos and video etc available at

The analysis presented in the paper was conducted with partial support from the Australian Government’s National Environmental Research

Background information

List of materials available:


The world’s coral reefs are being degraded, and the need to reduce local pressures to offset the effects of increasing global pressures is now widely recognized. This study investigates the spatial and temporal dynamics of coral cover, identifies the main drivers of coral mortality, and quantifies the rates of potential recovery of the Great Barrier Reef. Based on the world’s most extensive time series data on reef condition (2,258 surveys of 214 reefs over 1985–2012), we show a major decline in coral cover from 28.0%to 13.8% (0.53%y−1), a loss of 50.7% of initial coral cover. Tropical cyclones, coral predation by Crown-of-thorns starfish (COTS), and coral bleaching accounted for 48%, 42%,and 10%of the respective estimated losses, amounting to 3.38% y−1 mortality rate. Importantly, the relatively pristine northern region showed no overall decline. The estimated rate of increase in coral cover in the absence of cyclones, COTS, and bleaching was 2.85%y−1, demonstrating substantial capacity for recovery of reefs. In the absence of COTS, coral cover would increase at 0.89% y−1, despite ongoing losses due to cyclones and bleaching. Thus, reducing COTS populations, by improving water quality and developing alternative control measures, could prevent further coral decline and improve the outlook for the Great Barrier Reef. Such strategies can, however, only be successful if climatic conditions are stabilized, as losses due to bleaching and cyclones will otherwise increase.

Authors and key contacts

Dr Glenn De’ath – Principal Research Scientist at AIMS

Dr De’ath’s primary focus is on the statistical analyses of marine biological and environmental data, development of ecological methods, ecological modeling, development of software tools and systems for data analysis and spatial modeling and mapping. 

Dr Katharina Fabricius – Principal Research Scientist at AIMS

Dr Fabricius has worked as a coral reef ecologist since 1988, and presently holds the position of Principal Research Scientist at the Australian Institute of Marine Science. Her main research interests are to better understand roles and consequences of disturbances (especially ocean acidification, climate change and terrestrial run-off) on ecological processes in coral reefs. Within this framework, she has worked across a very broad range of scientific questions and organism groups, including corals, octocorals, crown-of-thorns starfish, coralline algae, sedimentation, marine snow, organic enrichment, water clarity, storms, bleaching, zooxanthellae, thermal tolerance, biodiversity, bioindicators, calcification, and the interactive effects of multiple stressors.

Dr Hugh Sweatman – Senior Research Scientist and Leader of AIMS Long-term Monitoring Program for coral reefs of the Great Barrier Reef

Dr Sweatman trained as a behavioural ecologist working on reef fishes and has worked on the GBR and in the Caribbean (Panama). His research interests have broadened to processes of disturbance and recovery on reefs, particularly as applied to the GBR. After graduating, he worked briefly at University of Sydney, then spent three years as a post-doc at the Smithsonian Tropical Research Institute in Panama. From 1990 he was a post-doc at James Cook University, initially studying fish predators of Acanthaster planci, then the effects of feeding fishes around tourist pontoons (Reef CRC). In 1995 he came to AIMS to lead the Long-term Monitoring Program.

Dr Marji Puotinen –  Honorary Fellow, University of Wollongong and Ohio State University

Dr Puotinen is a geographer using expertise in Geographic Information Science (GIS) to model tropical cyclone (hurricane) impacts on coral reefs worldwide.  Her PhD work at James Cook University reconstructed a cyclone disturbance history for the Great Barrier Reef over the recent past (1969-2003) using a combination of meteorological models implemented in GIS and field survey data of coral wave damage from cyclones.  She continues to refine this approach as well as apply it to characterise the timing, frequency and intensity of cyclone disturbance to reefs both globally and locally. 

Dr Peter Doherty – AIMS Research Fellow

After becoming expert on living brachiopods, Dr Doherty migrated from New Zealand to Australia where he also switched focus to the ecology and genetics of coral reef fishes, emphasizing processes driving the connectivity, replenishment and dynamics of their populations. After completing a PhD, he took a Queens Fellowship in Marine Science at AIMS – moving on a year later to join the School of Australian Environmental Studies, Griffith University. After teaching ecology and natural resource management for six years, he returned to AIMS as a staff scientist; eventually leading the Tropical Fisheries Ecology group. In 1999, he became a Program Leader in CRC Reef and soon after AIMS Research Director. In this role he facilitatated significant collaborations between AIMS and external partners through joint ventures like the “Great Barrier Reef Seabed Biodiversity Project”, the Marine and Tropical Sciences Research Facility, the CERF Marine Biodiversity Hub, and the Integrated Marine Observing System. 

Dr Jamie Oliver – AIMS Research Director

Dr Oliver joined AIMS in September 2009. Prior to this he worked for the WorldFish Center from 2000, first as senior scientist in charge of coral reef projects (including the Center’s ReefBase information system) and then as Director of Science Coordination and Secretary for the WorldFish Board of Trustees. He has also served as the Chair of the International Coral Reef Action Network Steering Committee and co-chair of the Global Coral Reef Monitoring Network Management Committee. Prior to WorldFish he was the Director of Information Support at the Great Barrier Reef Marine Park Authority and a senior scientist at the Australian Institute of Marine Science. During this period he conceived, and led the production of the first State of the Great Barrier Reef World Heritage Area Report and edited the first AIMS Long-term Monitoring Report for the GBR. He has carried out consultancy work on coral reef monitoring and management in many countries throughout Asia and the Pacific. 

John Gunn – AIMS Chief Executive Officer

John Gunn is the Chief Executive Officer of AIMS.  John has significant experience in leading development of strategy, scientific research and capability, and stakeholder engagement across a research portfolio encompassing marine ecology, fisheries, coastal systems, physical and chemical oceanography, atmospheric chemistry and climate science.  He joined AIMS from the position of Chief Scientist of the Australian Antarctic Program, where he played a key role in developing the new Australian Antarctic Science Strategy Plan: 2011 – 2021.  Prior to this, he was Deputy Chief of CSIRO’s Marine and Atmospheric Research Division, the culmination of 29 year career with the Commonwealth Scientific and Industrial Research Organisation.

John Gunn has held a number of important advisory and policy development roles through his membership of the Scientific Steering Committee for the Global Ocean Observing System, the Australian Academy of Science National Committee for Antarctic Research, the Antarctic Climate and Ecosystems Co‐Operative Research Centre Board, the Oceans Policy Science Advisory Group (OPSAG), the Commonwealth Government’s High Level Coordination Group on Climate Change Science, and Australia’s Integrated Marine Observing System Board.  

About AIMS:

The Australian Institute of Marine Science (AIMS) is a Commonwealth Government organisation and a leader in tropical marine science.

The Institute is consistently ranked among the top one per cent of specialist research institutions internationally and is known for its unique capacity to investigate topics from broad-scale ecology to microbiology.

AIMS is committed to the protection and sustainable use of Australia’s marine resources. Its research programs support the management of tropical marine environments around the world, with a primary focus on the Great Barrier Reef World Heritage Area, the pristine Ningaloo Marine Park in Western Australia and northwest Australia.

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Population outbreaks of the coral eating starfish Acanthaster planci have been responsible for 42% of the over 50% decline in coral cover on the Great Barrier Reef between 1985 and 2012 (credit: Katharina Fabricius, Australian Institute of Marine Science)

Horseshoe reef before Crown of Thorns invasion (credit: AIMS Long-term Monitoring Team)

Damage to Beaver Reef by Cyclone Hamish (credit: AIMS Long-term Monitoring Team)