How do we control crown-of-thorns starfish?

AMPTO diver/s monitoring and eradicating Crown-of-thorns Starfish

AMPTO divers monitoring and controlling 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.

Program growth and funding

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.

The Crown-of-thorns Starfish Control Program has been funded by the Australian Government since 2012. During 2019-20 the Program was partly funded through the Reef Trust Partnership (RTP) between the Great Barrier Reef Foundation (GBRF) and the Department of Agriculture, Water and the Environment (DAWE). For 2020-22 it is fully supported through the RTP by the GBRF and the DAWE. The Program’s manual in-water control component is delivered through a strategic partnership between the GBRF, Great Barrier Reef Marine Park Authority (the Marine Park Authority) and the Reef and Rainforest Research Centre (RRRC).

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 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.

Giant Triton Snail - copyright Great Barrier Reef Marine Park Authority

All hail the mighty giant triton snail!

Research breakthroughs

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.

National Environmental Science Program

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.

Red Crown of Thorn Starfish Great Barrier Reef landscape

Protecting coral on the Great Barrier Reef - crown-of-thorns starfish control program

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.