How do we control crown-of-thorns starfish?
The Crown-of-thorns Starfish Control Program was established in 2012 and delivers the tactical response to outbreaks, as part of the Marine Park Authority’s Crown-of-thorns Starfish Strategic Management Framework.
The program uses dedicated vessels with professionally-trained crews to manually cull starfish using lethal injection of either bile salts or household vinegar. Strategic surveillance and monitoring activities are also conducted as part of the Crown-of-thorns Starfish Control Program. This ensures culling efforts are targeted to locations with the greatest benefit, progress is measured, and pest management outcomes are maintained once they are achieved.
Supporting the environment and Reef communities
In addition to delivering environmental benefits for the health of the Great Barrier Reef, the Crown-of-thorns Starfish Control Program also delivers social and economic benefits for Australians. Since its inception, the program has been delivered in partnership with the Reef tourism industry through the Association of Marine Park Tourism Operators (AMPTO). Targeted crown-of-thorns starfish control keeps the reef healthy at sites where local tourism businesses bring their national and international guests to see the Great Barrier Reef. The program also trains and employs more than 100 people, primarily from Queensland.
Initially, the program had one or two dedicated vessels. However, over time the outbreak that began in 2010 in the northern management region spread south. 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.
As of 2019-20, five crown-of-thorns starfish control vessels are deployed in the northern, central and southern management regions of the Marine Park. Within each management region, control efforts are strategically targeted to focus on reefs of high ecological and economic value.
What is the goal of the Crown-of-thorns Starfish Control Program?
The Crown-of-thorns Starfish Control Program was established in 2012, several years after the initiation of the major outbreak that began in 2010 in the northern management region. As a result, the opportunity to take action to prevent or suppress the initiation of the current outbreak had already passed.
Consequently, the current goal of the Crown-of-thorns Starfish Control Program is to PROTECT coral in the Marine Park from crown-of-thorns starfish damage by reducing and maintaining crown-of-thorns starfish numbers at levels where their impact on coral is minimised.
This goal is directly aligned to the Australian and Queensland Government’s Reef 2050 Long-Term Sustainability Plan, which provides a clear target to address the crown-of-thorns starfish threat to ecosystem health:
Implement an integrated crown-of-thorns starfish management framework within the Marine Parks to guide and coordinate efforts by all partners to reduce coral predation and maximise live coral cover on identified reefs.
Minimising impact to coral cover
It is important to note that the goal of the Crown-of-thorns Starfish Control Program is focused on achieving crown-of-thorns starfish numbers that minimise their impact on coral cover, rather than using explicit coral cover targets. This is because coral cover itself is highly variable across reefs and regions in the Marine Park (there is no single coral cover target that would suit all locations), and also because changes in coral cover are influenced by many other factors in addition to crown-of-thorns starfish impacts.
Other drivers of change in coral cover include natural cycles of disturbance and recovery in coral communities, as well as major impacts from mass bleaching events and tropical cyclones. Therefore, the Crown-of-thorns Starfish Control Program is focused on managing crown-of-thorns starfish numbers to achieve levels that are ecologically sustainable for coral growth and recovery. The intervention program can have direct influence over this.
The goal of the Crown-of-thorns Starfish Control Program is not to cull large numbers of starfish (achieve high cull counts), nor is it to eradicate crown-of-thorns starfish from the Marine Park.
What science informs the delivery of the Crown-of-thorns Starfish Control Program?
The Crown-of-thorns Starfish Control Program applies the best-available science in its approach to tactical crown-of-thorns starfish response on the Great Barrier Reef, and has a track-record of ongoing adaptive management and improvement through its collaboration with research partners.
In 2014, scientific innovation delivered a significant improvement in 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 (NESP) Integrated Pest Management (IPM) research projects have delivered the science underpinning the Crown-of-thorns Starfish Control Program. These projects, which are administered through the Reef and Rainforest Research Centre’s Tropical Water Quality Hub, bring together Australia’s leading scientific experts from research institutions across the country to tackle the crown-of-thorns starfish threat. They deliver practical and applied research that fills critical knowledge gaps to inform effective pest management strategies.
Most recently, a NESP IPM 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. The ultimate goal of the decision support framework is to ensure that crown-of-thorns starfish are effectively controlled to ecologically sustainable levels that promote coral growth and recovery, and that those outcomes are maintained once they are achieved.
IPM decision support framework
Since November 2018, the Marine Park Authority has applied this IPM decision support framework in delivering the Crown-Of-Thorns Starfish Control Program on the Great Barrier Reef. The application of this science has been a major 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.
The Marine Park Authority will continue to adapt and improve its approach to crown-of-thorns starfish management based on scientific advances, and will look to integrate new pest management methods, tools and technologies into the Crown-of-thorns Starfish Control Program as they become available.
How do we decide which reefs to control?
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.
What pest management actions do we take at high value reefs?
There are three on-water activities that Crown-of-thorns Starfish Control Program vessel crews use to achieve crown-of-thorns starfish numbers that 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 are used to estimate coral cover to inform culling efforts.
- Culling – snorkel or scuba dives that involve systematic searches of a defined area on a high value reef, with 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 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 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.
What performance metrics do we track?
The Crown-of-thorns Starfish Control Program tracks a number of performance metrics across high value reefs in order 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 is used to track 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 they are first visited for pest management, with some reefs already having severe infestations while other reefs may have relatively low numbers.
- Manta tow surveillance provides a baseline assessment of crown-of-thorns starfish numbers across a reef, in order to assess its initial ‘Outbreak Status’ prior to pest management.
- This ‘Outbreak status’ assessment is then repeated roughly every 3-6 months to track changes in crown-of-thorns starfish numbers during and after the pest management process.
- For reefs that are initially assessed as having ‘No Outbreak’ proactive control is undertaken wherever crown-of-thorns starfish and/or crown-of-thorns starfish scars are observed in order 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 achieve ‘No Outbreak’ status.
Catch-per-unit effort (CPUE, site level metric)
- This metric is used to track changes in crown-of-thorns starfish numbers at a site level during the pest management process, as dive teams work to achieve numbers that are sustainable for coral.
- Crown-of-thorns starfish have a tendency to aggregate together in groups, and these groups move around on a reef over time as the starfish search for new feeding ground.
- 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 coral cover).
- When cull sites are heavily infested with a large density of starfish, it may take a number of repeated voyages to achieve the ecologically sustainable CPUE target at a site.
- The goal of pest management is 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 as a whole 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 levels that are ecologically sustainable for coral growth and recovery.
The ‘Outbreak Status’ metric provides a broad scale assessment of crown-of-thorns starfish numbers across an entire reef, whereas the CPUE metric provides more detailed information on crown-of-thorns starfish numbers at a site level.
The CPUE metric is more sensitive than the ‘Outbreak status’ metric, because cull divers are able to search for cryptic crown-of-thorns starfish during cull dives. As a result, a reef may have achieved ‘No Outbreak’ status but still have a few cull sites where crown-of-thorns starfish numbers are above the ecological threshold. It is only when both ‘No Outbreak’ status and CPUE targets are achieved at all cull sites that a reef is considered effectively managed.
How do I access data from the Crown-of-thorns Starfish Control Program?
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.