The Great Barrier Reef Marine Park Authority runs a crown-of-thorns starfish control program to protect a network of priority coral reefs from outbreaks of coral-eating starfish. Controlling crown-of-thorns starfish is a key initiative under our Reef Blueprint, which outlines the top 10 actions to protect the Reef.
Why control crown-of-thorns starfish
The crown-of-thorns starfish, Acanthaster cf. solaris, is native to the Great Barrier Reef. The starfish are a voracious predator of live coral, have a very high reproductive potential, grow 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.
There have been four major recorded outbreaks on the Great Barrier Reef since the 1960s, each lasting approximately 10 years. The most recent outbreak started in 2010 and is currently spread along parts of the Great Barrier Reef.
Outbreaks are one of the major sources of coral mortality across the Great Barrier Reef Marine Park, driving coral decline on a scale comparable to cyclones and severe bleaching events. However, unlike cyclones and bleaching events, crown-of-thorns starfish outbreaks can be predicted and controlled.
Efforts to reduce the impact of crown-of-thorns predation on coral have become increasingly critical given the cumulative impacts to coral cover from other threats, such as climate change, coral bleaching, tropical cyclones and decreased water quality.
The Great Barrier Reef Blueprint for Resilience identified crown-of-thorns starfish control as one of the most feasible actions to reduce coral mortality and improve resilience on the Great Barrier Reef.
The crown-of-thorns starfish control program
The first broad-scale, government-funded crown-of-thorns starfish control program began in 2012. To date the control program has been successful in maintaining starfish densities below ecologically sustainable thresholds for coral growth on 75 per cent of the 57 priority reefs between Port Douglas and Townsville.
Based on this success, in 2017 and 2018 the Great Barrier Reef Authority received additional funding to expand the existing crown-of-thorns starfish control program. The goals of the expanded program are to:
- protect coral cover at reefs that are critical sources of coral larvae to facilitate Reef recovery and resilience
- protect coral cover at reefs of high value for the tourism industry
- reduce the spread of the outbreak by culling at reefs that have greatest risk of spreading crown-of-thorns starfish larvae.
There are over 3000 reefs in the Marine Park across 344,400 square kilometres. Even with the increased resources, the Marine Park Authority needs to be strategic about allocating resources to effectively deliver the control program.
Priority reefs have been identified based on a range of information, including connectivity modelling predictions, tourism visitation data, the current coral cover, crown-of-thorns starfish outbreak status of reefs, and operational capacity to effectively control them.
All these factors were considered to focus program efforts and resources to make the biggest positive impact on the resilience of the Reef and the industries it supports.
Through a competitive tender process commencing in late 2017 the Marine Park Authority expanded the program from two to six vessels in 2018. Delivery of the crown-of-thorns starfish control program will be completed through agreements with:
- Blue Planet Marine
- Pacific Marine Group Pty Ltd
- Reef and Rainforest Research Centre
- Ultra Coral Australia Pty Ltd.
Each vessel has been assigned an area of operation, with a list of priority reefs to target.
Suppliers will complete crown-of-thorns starfish surveillance, culling, reef health surveys and provide support for crown-of-thorns starfish research.
The overarching management goals for the vessels are to cull crown-of-thorns starfish aggregations below scientifically established thresholds to ensure coral growth outpaces their feeding rate, and to achieve a ‘no outbreak’ status across the priority reefs. The management goal is not to eradicate crown-of-thorns starfish on reefs or try and achieve high cull counts.
Crown-of-thorns starfish control guidelines outline control methods, how the project is being implemented and relevant biology and ecology.
The Marine Park Authority recognises that crown-of-thorns starfish management needs to be dynamic and adaptive.
The Marine Park Authority works cooperatively and relies on the National Environmental Science Program (NESP) Integrated Pest Management Program to provide advice to continually improve crown-of-thorns starfish control.
Consistent and repeated culling treatments are essential to keep starfish densities beneath thresholds. Management decisions are informed by analysis and review of the data collected by the culling vessels.