Why do we manage crown-of-thorns starfish in the Marine Park?
Crown-of-thorns starfish outbreaks cause significant damage to coral reefs across large spatial scales, and are one of the major causes of coral decline across the Great Barrier Reef over the past 40 years.
The damage from crown-of-thorns starfish outbreaks adds to the damage from other major causes of coral decline — tropical cyclones and coral bleaching events. Out of these three major causes of coral decline, crown-of-thorns starfish outbreaks are the only one that can be mitigated through direct local management.
The Outlook Report identifies crown-of-thorns starfish outbreaks as a significant threat to the long-term health of the Great Barrier Reef ecosystem. The Reef 2050 Long-Term Sustainability Plan and the Great Barrier Reef Blueprint for Resilience outline key management actions that should be taken to reduce threats to the Reef, including management of crown-of-thorns starfish outbreaks.
Minimising the impact of crown-of-thorns starfish outbreaks is considered one of the most scalable and feasible direct management interventions available today to enhance the Great Barrier Reef’s long-term health and resilience in the face of climate change.
By taking direct action to protect coral, crown-of-thorns starfish management complements other initiatives that are under development in the Reef Restoration and Adaptation Program, thus supporting the Great Barrier Reef’s capacity to resist, repair and recover from the impacts of a changing climate.
How do we manage crown-of-thorns starfish in the Marine Park?
Since the 1980s, the Great Barrier Reef Marine Park Authority (the Marine Park 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 Marine Park 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.
- This strategic and adaptive crown-of-thorns starfish management framework includes:
- preventative actions to address factors that may contribute to the initiation and spread of outbreaks
- tactical actions by the Crown-of-thorns Starfish Control Program to reduce the damage caused by outbreaks when they occur
- monitoring to provide an early warning of developing outbreaks and guide tactical action
- research priorities that are most critical to improving crown-of-thorns starfish management.
Our Crown-of-thorns Starfish Strategic Management Framework provides the guiding principles to actively manage crown-of-thorns starfish now while also promoting and supporting research and innovation to improve crown-of-thorns starfish management into the future.
It recognises that effectively addressing the crown-of-thorns starfish threat requires coordination across the state and federal government agencies, research institutions, Reef-based industries, and community action groups. The Crown-of-thorns Starfish Strategic Management Framework seeks to inform, empower and guide these groups to deliver a coordinated approach to crown-of-thorns starfish management in the Great Barrier Reef Marine Park.
Although the Crown-of-thorns Starfish Strategic Management Framework is focused on the Great Barrier Reef Marine Park, the general management principles can be applied in other coral reef areas where crown-of-thorns starfish outbreaks occur, both nationally (for example, the Torres Strait) and internationally.
Reef in Focus: Starfish - The Clone Wars
We take a deep dive into the significant challenge of managing crown-of-thorns starfish, the devastating effects this coral-eating pest has on the Reef and the importance of the Crown-of-thorns Starfish Control Program in protecting coral cover to underpin Reef biodiversity and resilience.
Our guests include Reef Authority Chief Executive Officer Josh Thomas; Reef Authority Director of Reef Interventions Dr Roger Beeden; Reef Authority Assistant Director of Crown-of-thorns Starfish Control Program David Williamson; and Senior Research Scientist from the Australian Institute of Marine Science Dr Mike Emslie.
All the Great Barrier Reef Marine Park users, including community members and industry stakeholders, are encouraged to engage in crown-of-thorns starfish management.
- There are two primary ways you can help:
- Report crown-of-thorns starfish sightings to the Marine Park Authority using the Eye on the Reef Sightings app. This crown-of-thorns starfish sightings information may then be used to guide more in-depth assessments by reef managers, marine parks rangers and/or Crown-of-thorns Starfish Control Program vessel crews.
- Protect your patch by culling crown-of-thorns starfish in your local area. If you choose to do this, please consult the Marine Park Authority’s Crown-of-thorns Starfish Control Guidelines. These guidelines provide important information on how to conduct this activity safely and effectively. Permits are required to conduct culling in some Marine Park Zones. Check requirements here. If required, crown-of-thorns starfish control permit applications have no assessment fee and can be submitted through the Permits Online application portal.
- A few important health and safety tips for those interested in culling crown-of-thorns starfish to protect their local patch:
- Crown-of-thorns starfish have hundreds of long needle-like venomous spines covering their bodies and arms, presenting a health and safety risk to people who interact with them
- Reaction to a crown-of-thorns starfish spike can vary considerably among people, ranging from localised pain and swelling at the puncture site to severe anaphylactic shock
- People undertaking crown-of-thorns starfish culling activities need to take suitable precautions to avoid being spiked (for example, wear personal protective equipment) and should also be confident in the appropriate first aid treatment before doing the activity.
- A few important tips to ensure that your crown-of-thorns starfish culling efforts are effective:
- The recommended method for crown-of-thorns starfish culling involves injecting starfish at the base of an arm with approved solutions (for example, bile salts or household vinegar)
- If the dosage and injection technique is delivered correctly, these solutions can be highly effective at killing crown-of-thorns starfish in under 48 hours
- Culling through lethal injection is safer than collection and burial onshore because it does not require handling this venomous starfish
- Do not attempt to kill crown-of-thorns starfish by cutting them into pieces because pieces of a single starfish can regenerate into multiple starfish and make the problem worse
- It takes some skill and practice to cull effectively using the injection technique, please refer to the Crown-of-thorns Starfish Control Guidelines for more tips.
- Crown-of-thorns Starfish Strategic Management Framework
- Crown-of-thorns Starfish Control Guidelines
The Pacific crown-of-thorns starfish (COTS), Acanthaster cf. solaris, is a marine invertebrate that is native to the Great Barrier Reef. These starfish also naturally occur on coral reefs throughout the Indo-Pacific region, and closely related starfish species also occur across reefs in the Indian Ocean and the Red Sea.
These starfish feed exclusively on live coral as adults can grow rapidly to reach maturity and produce large numbers of offspring once they mature. Because of these life history characteristics, populations of these starfish can grow to reach ‘outbreak’ numbers where they become a pest and cause significant damage to coral reefs.
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. The southern spread of these outbreaks happens mainly through the transport of crown-of-thorns starfish larvae on ocean currents.
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.
Further information on patterns of outbreaks over time across the Great Barrier Reef is available through the Australian Institute of Marine Science Long-term Monitoring Program.
This question has long been researched and debated in the scientific community. Through this research, it has become increasingly clear that there is unlikely to be one single factor that causes outbreaks to start.
- Instead, it is likely to be a combination of factors that together provide the conditions for outbreak initiation, including:
- The biological traits of the starfish themselves, enable crown-of-thorns starfish populations to grow and reproduce rapidly in the right conditions
- reductions in the abundance of natural predators of crown-of-thorns starfish, which may enhance the ability of crown-of-thorns starfish populations to grow and reach outbreak numbers
- excess nutrients from run-off or natural up-welling that provides extra food for crown-of-thorns starfish larvae to survive and multiply
- patterns of ocean currents that spread crown-of-thorns starfish larvae in such a way that promotes the development of outbreaks
- the availability of sufficient live coral as a food source supports outbreak numbers.
Crown-of-thorns starfish usually occur on coral reefs in low numbers (for example, a few starfish per hectare of reef habitat). When in low numbers, starfish feeding causes mortality of individual coral colonies on a local scale but is unlikely to cause a decline in coral cover across an entire reef.
Outbreaks occur when starfish numbers become unsustainable for coral growth and recovery. This means that starfish numbers increase to levels where the impact of their feeding is expected to cause a decline in coral cover across an entire reef.
Individual reefs across the Marine Park experience varying severity of crown-of-thorns starfish outbreaks, with some reefs becoming severely infested, some reefs mildly infested, and some reefs not impacted by an outbreak.
This variability in crown-of-thorns starfish impact amongst reefs poses a challenge to managers, particularly given the immense spatial scale of the Great Barrier Reef Marine Park (~3,000 reefs across 344,440 km2). Consequently, it is impossible to know the 'Outbreak Status' of every individual reef in the Marine Park at any time.
Regular monitoring of crown-of-thorns starfish numbers helps managers understand a reef's current 'Outbreak Status' and identify when crown-of-thorns starfish numbers are beginning to increase to unsustainable levels. The two main survey techniques used to monitor crown-of-thorns starfish numbers across reefs in the Marine Park are manta tow surveys and Reef Health and Impact Surveys.
The 'Outbreak Status' thresholds used by the Marine Park Authority are derived from scientific research. They are tailored to the particular survey technique used to estimate the number of crown-of-thorns starfish on a reef.
These thresholds indicate the average number of crown-of-thorns starfish on a reef that is unsustainable for coral.
|Outbreak Status of a reef||Impact on coral at that reef||The average number of crown-of-thorns starfish per manta tow survey||The average number of crown-of-thorns starfish per RHIS|
|No outbreak||Crown-of-thorns starfish numbers are sustainable for coral||≤ 0.1||≤ 0.024|
|Potential||Crown-of-thorns starfish numbers may cause a coral decline||> 0.1||> 0.024|
|Established||Crown-of-thorns starfish numbers will cause a coral decline||> 0.22||> 0.05|
|Severe||Crown-of-thorns starfish numbers will cause severe coral decline||> 1.0||> 0.24|