Crown-of-thorns starfish control program

The Crown-of-thorns Starfish Control Program supports coral growth and recovery by effectively controlling the coral predator to ecologically sustainable levels.

Crown-of-thorns starfish are a native coral predator on the Great Barrier Reef. In outbreak proportions, they have been responsible for causing equal, if not greater declines in coral cover as other major disturbances on the Reef, including mass coral bleaching and severe tropical cyclones.

The Reef Authority and partners are successfully protecting Great Barrier Reef resilience through effective management of crown-of-thorns starfish outbreaks.

Did you know that with sustained resourcing and effort we can:
Reducing numbers of crown-of-thorns starfish on one reef, suppresses the spread of outbreaks to neighbouring reefs and regions
Timely response to outbreaks gives corals the best chance of survival
Corals have more capacity to handle other threats when they aren’t facing crown-of-thorns starfish outbreaks.

When implemented with sustained and dedicated effort, crown-of-thorns starfish control has proven to be an effective scalable method for reducing the cumulative pressures of impacts facing reef ecosystems.

A highly collaborative effort, the Program is run in partnership with the Great Barrier Reef Foundation and Reef and Rainforest Research Centre along with supporting government agencies, industry partners and contractors.

Reef managers, researchers, Program contractors, and the tourism industry and operators have worked in partnership over the past decade to deliver crown-of-thorns control operations at increasing spatial scales.

The program coordinates vessels and trained crews dedicated to delivering comprehensive reef surveillance, reef health surveys, manual culling of starfish, and research support.

A targeted approach

With over 3,000 reefs spread across 344,000km2 in the Marine Park, the Control Program uses a combination of data and modeling to prioritise reefs based on their ecological and economical value to the wider Reef. It combines the latest information including real-time and historic reef-level crown-of-thorns populations, larval connectivity modelling, and observations from Program partners, contractors, and reef visitors.

The reef prioritisation process has evolved to identify 500 reefs to focus on protecting coral cover through this program. Each year, the Program, with the assistance of contractors and partners, targets between 200 and 250 of these Reefs to stay on top of the starfish’s population.

Today, the Reef Authority’s Crown-of-thorns Control Program applies the best-available science in its approach to tactical response on the Great Barrier Reef and leads the process to prioritise reefs for crown-of-thorns management. The tactics deployed are responsive and incorporate real-time information. It is supported by the latest evidence and research delivered through the Crown-of-thorns Control Innovation Program.

The Reef Authority’s Crown-of-thorns Starfish Strategic Management Framework outlines the strategic approach to achieving the crown-of-thorns starfish management targets from the Reef 2050 Long-Term Sustainability Plan and the Great Barrier Reef Blueprint for Resilience.

During 2023-24 the Program:
Actioned 192 target reefs
Protected 11,640 hectares of reef habitat through targeted culling
Culled 50,227 crown-of-thorns starfish
Spent 16,657 hours underwater

Long-term monitoring of crown-of-thorns starfish across the Great Barrier Reef, has shown that suppressing the population of these adult starfish has widespread benefits past the immediate reef it they were removed on. Larval distribution of crown-of-thorns starfish can disperse throughout neighbouring reefs and even adjoining sectors thanks to the ocean currents they travel on.

Searching for crown-of-thorns starfish

When a Control Program vessel reaches a target reef, the team undertakes an initial monitoring survey of the health of that reef. Using a manta-tow, a single snorkeler is towed behind a small vessel with a clipboard. The initial monitoring uses Eye on the Reef survey methods to record coral condition including cover, recording any coral disease, evidence of coral predators, and key indicator species. This information is collated into the broader database to help guide management decisions.

Where outbreaks are identified, a team of divers are deployed to undertake finer scale monitoring and intervention. A series of search swims lets divers seek out the starfish hiding amongst corals which may not have been seen from the surface. Using a single injection of household vinegar or ox bile, divers systematically and efficiently cull populations down to sustainable levels.

History of outbreaks and the program

Four contemporary major crown-of-thorns starfish outbreaks have been documented on the Great Barrier Reef — beginning in the 1960s, the late 1970s, the early 1990s and the current outbreak, which was first detected in 2010.

Oral histories and anecdotal accounts also suggest there were crown-of-thorns starfish outbreaks on the Great Barrier Reef prior to the 1960s, although the frequency and severity of these historical outbreaks are not well understood.

The four contemporary major crown-of-thorns starfish outbreaks on the Great Barrier Reef have followed a similar pattern of initiation and spread. The outbreaks begin about every 15 years on reefs between Lizard Island and Green Island, in the northern management region of the Marine Park. This region is generally referred to as the ‘initiation box’.

The outbreaks then spread southward down the length of the Great Barrier Reef over a period of at least 10-12 years.

Crown-of-thorns starfish outbreaks have also been documented periodically in the remote Swain Reefs, located at the far southern end of the Marine Park. These outbreaks are thought to develop separately from the outbreaks that begin in the north.

This means crown-of-thorns starfish outbreaks are impacting the Great Barrier Reef most of the time, although the spatial location of that impact changes over time.

Since the 1980s, the Reef Authority has worked in partnership with research institutions, government agencies, and the tourism industry to understand the dynamics and causes of crown-of-thorns starfish outbreaks and implement management responses.

The Crown-of-thorns Starfish Control Program was established in 2012 and delivers the tactical response to outbreaks as part of the Reef Authority’s Crown-of-thorns Starfish Strategic Management Framework.

In 2014, scientific innovation significantly improved the efficiency of culling operations using a single-shot injection of bile salts. Prior to that, injections with sodium bisulphate required 10-25 injections per starfish, making control efforts very slow and labour intensive.

Subsequent research extended the single-shot injection breakthrough by demonstrating that household vinegar could also be used to effectively cull starfish using a refined dosage and injection method.

Beginning in 2015, the National Environmental Science Program’s Integrated Pest Management (IPM) research projects have delivered the science underpinning the Crown-of-thorns Starfish Control Program.

These projects, administered through the Reef and Rainforest Research Centre’s Tropical Water Quality Hub, bring together Australia’s leading scientific experts from research institutions to tackle the crown-of-thorns starfish threat. They deliver practical, applied research that fills critical knowledge gaps to inform effective pest management strategies.

A National Environmental Science Program research project has delivered a decision support framework designed to increase the efficiency and effectiveness of manual, diver-based crown-of-thorns starfish control. This decision support framework provides clear step-by-step pathways to support evidence-based decision-making on the water and guides efficient use of program resources across a vessel fleet.

Integrated Pest Management decision support framework

Since November 2018, the Reef Authority has applied this Integrated Pest Management decision support framework in delivering the Crown-Of-Thorns Starfish Control Program on the Great Barrier Reef.

Applying this science has been a significant step forward in our approach to pest management, making the Crown-of-thorns Starfish Control Program more strategic and effective than previous control programs on the Great Barrier Reef or globally.

In 2018, funding for the Crown-of-thorns Starfish Control Program was increased. This additional funding enabled the program to expand from two to six vessels in 2018-19. The expansion of the program enabled crown-of-thorns starfish control vessels to be deployed in the far north and far south of the Marine Park for the first time.

In 2023, the Crown-of-thorns Starfish Control Program received the Biodiversity category award at the 34th Banksia National Sustainability Awards, one of Australia's oldest and most prestigious sustainability awards.

The Reef Authority will continue to adapt and improve its approach to crown-of-thorns starfish management based on scientific advances. It will look to integrate new pest management methods, tools and technologies into the Crown-of-thorns Starfish Control Program as they become available.

There are over 3,000 reefs spread across 344,400 km2 in the Great Barrier Reef Marine Park that are potentially impacted by starfish outbreaks. It is not possible to protect every reef, given this vast spatial scale and the inherently limited resources available for pest management. Instead, informed decisions must be made about how to prioritise limited resources to achieve the greatest benefits for the health of the Great Barrier Reef ecosystem and the industries it supports. This planning takes into account the expected ecological and economic benefits, risks, costs, and available resources.

The Marine Park Authority uses the best available science and information to strategically target reefs of high ecological and economic value for pest management. A wide range of information is considered when identifying these high value ‘priority’ reefs, including:
Monitoring data on the ‘Outbreak status’ of reefs across the Marine Park
Reports of crown-of-thorns starfish Sightings received from the Eye on the Reef Sightings app
Tourism visitation data
Marine Park Zoning and regulations
Modelling predictions that indicate reefs with higher capacity to support reef recovery
Modelling predictions that indicate reefs with higher capacity to spread outbreaks
Logistical and operational knowledge (for example, depth and exposure profiles of reefs).
This strategic planning takes into consideration identified regions of the Marine Park with concentrated crown-of-thorns starfish impacts (for example, current outbreak front), and also regions that are predicted to have an emerging risk of developing outbreaks. It is intended to focus limited resources on the places where they will have the greatest benefit, while at the same time allowing for agility and adaptive management based on new information.

Three on-water activities that Crown-of-thorns Starfish Control Program vessel crews use to achieve crown-of-thorns starfish numbers are ecologically sustainable for coral growth and recovery across high-value reefs. Together, these activities collect the information required to make effective pest management decisions in accordance with the NESP IPM decision support framework.

Manta tow Surveillance – Snorkel surveys that collect information on the number of crown-of-thorns starfish, crown-of-thorns starfish feeding activity, and coral cover across high-value reefs. In the context of the Crown-of-thorns Starfish Control Program, these surveys are used to decide where to deploy cull divers and also to assess progress in achieving management goals.
Reef Health and Impact Surveys (RHIS) – Snorkel or scuba dive surveys that collect information on coral cover and factors that may impact coral cover on high-value reefs, including crown-of-thorns starfish, coral bleaching, coral disease, and physical damage. In the context of the Crown-of-thorns Starfish Control Program, these surveys estimate coral cover and inform culling efforts.
Culling – Snorkel or scuba dives that involve systematic searches of a defined area on a high-value reef, with a lethal injection of all crown-of-thorns starfish found. Cull divers record information on the number and size of starfish culled and the number of minutes spent searching. This information is used to calculate a catch-per-unit effort (CPUE). In the context of the Crown-of-thorns Starfish Control Program, culling is used to reduce crown-of-thorns starfish numbers down to threshold levels that promote coral growth and recovery. These ecologically sustainable numbers of crown-of-thorns starfish vary depending on coral cover, because reefs with lower coral cover can support fewer crown-of-thorns starfish compared to reefs with higher coral cover.

If the average coral cover on a high-value reef is >40%, then culling should aim to achieve a CPUE below 0.08 crown-of-thorns starfish culled per minute or 3 crown-of-thorns starfish per 40 minutes spent searching.

If the average coral cover on a high-value reef is <40%, then culling should aim to achieve a CPUE below 0.04 crown-of-thorns starfish culled per minute, or 1 crown-of-thorns starfish per 40 minutes spent searching.

The Crown-of-thorns Starfish Control Program tracks the number of performance metrics across high-value reefs to measure progress in reducing and maintaining crown-of-thorns starfish numbers at levels where their impact on coral is minimised.

Outbreak Status (reef level metric):
This metric tracks broad-scale changes in crown-of-thorns starfish numbers across an entire reef before, during and after the pest management process.
Crown-of-thorns starfish numbers are highly variable amongst reefs when first visited for pest management, with some reefs already having severe infestations. In contrast, other reefs may have relatively low numbers.
Manta tow surveillance provides a baseline assessment of crown-of-thorns starfish numbers across a reef to assess its initial ‘Outbreak Status’ before pest management.
This ‘Outbreak status’ assessment is repeated roughly every 3-6 months to track changes in crown-of-thorns starfish numbers during and after the pest management process.
For reefs initially assessed as having ‘No Outbreak, ’ proactive control is undertaken wherever crown-of-thorns starfish and/or crown-of-thorns starfish scars are observed to maintain their ‘No Outbreak’ status.
For reefs that are initially assessed as having ‘Potential’, ‘Established’ or ‘Severe’ outbreaks, intensive control is undertaken to reduce crown-of-thorns starfish numbers to achieve ‘No Outbreak’ status.

Catch-per-unit effort (CPUE, site level metric):
This metric track crown-of-thorns starfish numbers at a site level during the pest management process as dive teams work to achieve sustainable numbers for coral.
Crown-of-thorns starfish tend to aggregate together in groups, and these groups move around on a reef over time as the starfish search for new feeding grounds.
Each cull site on a reef is approximately 10 hectares in size and is systematically searched by dive teams for the presence of the cryptic starfish, and all starfish located are culled.
Cull divers aim to achieve a CPUE that is ecologically sustainable for coral growth and recovery (i.e. 0.04 or 0.08 crown-of-thorns starfish culled per minute, depending on the coral cover).
When cull sites are heavily infested with a large density of starfish, it may take several repeated voyages to achieve the ecologically sustainable CPUE target at a site.
Pest management aims to achieve this CPUE target at every cull site on a reef where crown-of-thorns starfish activity is detected.
Only when all cull sites across a reef have achieved this CPUE will the reef be considered to have crown-of-thorns starfish numbers that are sustainable for coral.

These two metrics are used in combination to assess progress in achieving and maintaining crown-of-thorns starfish numbers at ecologically sustainable levels for coral growth and recovery.

All data collected through the Crown-of-thorns Starfish Control Program is available for sharing under Creative Commons license.

The Marine Park Authority routinely prepares and shares datasets with research partners and other interested stakeholders. If you would like to access Crown-of-Thorns Starfish Control Program data please contact the Marine Park Authority and we will prepare datasets to suit your needs.

Important information for crown-of-thorns starfish control

The Great Barrier Reef Marine Park Regulations 2019 came into effect on 1 April 2019, providing more flexibility in crown-of-thorns starfish control.

The crown-of-thorns starfish (COTS), Acanthaster cf. solaris, is native to the Great Barrier Reef. The starfish is a voracious predator of live coral, have a very high reproductive potential, grows rapidly to reach maturity, and can reach ‘outbreak’ densities causing significant damage to coral reefs.

The frequency and severity of outbreaks are influenced by multiple factors, including major flooding events resulting in excess nutrients running off the land and a reduction in natural predators of the starfish.

If choosing to participate in crown-of-thorns starfish control, there are a number of very important sources of information you must familiarise yourself with:

Check zoning!

Zoning helps to manage and protect the values of the Marine Park that people enjoy. Each zone has different rules for the activities that are allowed, the activities that are prohibited, and the activities that require a permit.

Zones may also place restrictions on how some activities are conducted. Check the zoning map for the area you intend on visiting.

Do I need a permit?

The following table outlines which zones require a permit for crown-of-thorns starfish control.

Great Barrier Reef Marine Park Zone Permit requirements
General Use Zone No permit required - refer to Crown-of-thorns Starfish Control Guidelines
Habitat Protection Zone No permit required - refer to Crown-of-thorns Starfish Control Guidelines
Conservation Park Zone No permit required - refer to Crown-of-thorns Starfish Control Guidelines
Buffer Zone Permit required
Scientific Research Zone Permit required
Marine National Park Zone Permit required
Preservation Zone Permit required

Crown-of-thorns Starfish Control Guidelines

Please refer to the Crown-of-thorns Starfish Control Guidelines.

It is critically important to only use the control methods outlined in the Crown-of-thorns Starfish Control Guidelines (pages 2 – 7). Other methods, such as cutting up starfish, can make the problem worse.
Health and safety: COTS have hundreds of long needle-like toxic spines covering their bodies and arms, presenting a health threat to people who interact with them. Individuals undertaking COTS control activities need to take suitable precautions to avoid being spiked and should be confident in the appropriate first aid treatment before doing the activity.

Report what you see and your achievements

Eye on the Reef is a reef monitoring and assessment program that enables anyone who visits the Great Barrier Reef to contribute to its long-term protection by collecting valuable information about reef health, marine animals and incidents.

If you participate in crown-of-thorns starfish control, please take photos of what you are seeing and load your information into the Great Barrier Reef Marine Park Authority’s Sightings Network. Please include the number of Crown-of-thorns removed.

We appreciate your information sharing as we can combine it with the knowledge of the program’s control efforts to offer the best management outcomes possible to protect the Reef.

Crown-of-thorns starfish control program

The goal of the Marine Park Authority’s crown-of-thorns starfish control program is to protect coral from starfish predation on high-value reefs in the Marine Park. This is achieved by culling starfish to bring their numbers down to ecologically sustainable levels for coral growth and recovery.

The management objectives of the control program progress through different stages (prevention, suppression, containment and protection) as the dynamics of the outbreak progress over time (See below Figure).

In 2018, the secondary outbreaks that began in 2010 were well underway, and the control program continued to focus on the protection of coral at high-value sites in the Marine Park.

Recent research has shown the crown-of-thorns starfish control program to be effective in reducing starfish numbers and improving hard coral cover at sites where culling is regularly carried out.

Culling vessel operations are guided by science and scouting surveys undertaken by cull vessels and the Reef Joint Field Management Program.

Outcomes are measured by comparing coral cover and starfish densities at high-value target reefs before culling begins, and then monitoring over time to ensure culling efforts do not cease until starfish densities fall below a threshold needed to support coral recovery.

John Brewer Reef, one of the high value sites prioritised for culling, located 70 kilometres offshore from Townsville, is an important reef for recreational fishing and diving. During the first survey in November 2018, the reef was experiencing a severe outbreak with an average of 3.5 starfish counted per survey (See below Figure).

Intensive culling operations at this reef began following the initial survey, and over several months a team of trained diversculled more than 20,000 starfish to bring starfish numbers down to levels that minimise their impact on corals.

In March 2019, another round of surveys revealed that culling had reduced the severity of the outbreak, with an average of 0.35 starfish counted per survey (Figure 7.5).

Hard coral cover was maintained at an average of 31–42 per cent throughout intensive culling operations. This high-value reef will continue to be visited by the control program vessels to further reduce starfish numbers and protect coral.

A targeted approach

Searching for crown-of-thorns starfish

History of outbreaks and the program

Integrated Pest Management decision support framework