Implementation of the Crown-of-thorns research strategy: regional strategies

Dave Westcott
Led by: Dr David Westcott, CSIRO


Project Summary

Crown-of-thorns starfish (COTS) management requires decisions be made about where to invest control effort in order to achieve regional scale objectives, e.g. to modify COTS spread or to facilitate coral recovery. However, no objective basis for choosing sites exists, beyond their economic importance, meaning that achieving these important goals is largely left to chance. This project will leverage past and current research to develop a decision support framework to assist in prioritizing reefs for control and for assessing alternative strategies by integrating the full range of ecological and management information available. Field and desktop research will also be conducted to fill critical knowledge gaps and to assess the prospects of new control technologies.

Problem Statements


Decisions about where to invest control effort must be made at two distinct spatial scales. Large scale outcomes, e.g. preventing COTS spread, require decisions about where within a region investing in control will produce the desired outcomes. Then at those local areas decisions on where and when to control must be made. Currently managers have little to guide them in terms of how best to distribute their management effort at either of these scales and no means of assessing the likely outcomes of the alternative options available to them. Consequently, investment choices, beyond the protection of economically important sites, have not been optimal.

How Research Addresses Problem

The work outlined in this proposal will provide managers with a framework for assessing how and where to invest in COTS control at the regional scale. This will be achieved by integrating research on patterns of connectivity between reefs on the GBR, data on the ecology and dispersal of COTS and corals, and an understanding of the capacity and constraints under which the control program operates. This framework will be designed to guide decisions at the regional scale but will be integrated with the local-area decision support tools being developed in NESP2.1.1. This combination will provide managers with a robust system for planning COTS control activities and for assessing and refining the strategies and objectives of the approaches they employ. The work required to achieve this goal includes desktop reviews, modelling, field ecology and laboratory studies that will be funded from NESP3. The work will be supported by external proposals on COTS dispersal and recruitment to be submitted under the auspices of the COTS Working Group (formed in NESP1.1.1).

In NESP 3 we will develop a Regional Scale Decision Support Framework to assist in choosing where within a region (i.e. in which local area) to invest in control. The work will build on the connectivity models developed under a series of previous projects. In this work these static, physical models will be refined to improve their spatial resolution and to make them dynamic (i.e. able to reflect seasonal and annual variation). They will then be integrated with population models to provide updatable ecological realism. Finally, they will be packaged into a user friendly format to allow for their use in designing and assessing management strategies.

These models will be complimented by a range of field and desktop studies intended to inform the decision support tools and to assess future control technologies. These include:

1. Assessment of deepwater habitat for COTS

Limitations on dive time and depth mean that the COTS control is concerned with the top 15m of reef. However, we know that: i) COTS occur to depths as great as 50m, ii) there are anecdotal reports that COTS move into controlled areas from deeper habitat, and iii) reports from elsewhere indicate that controlling COTS below 20m is critical for lasting control. If deep habitat is significant, as this information suggests, then identifying this will be critical to designing successful programs and will require significant changes to current management practice. This work will identify the extent of deep water habitat in the control program area, its use by COTS and the implications of this for the design of the control program.

2. CoTS movement on longer timescales

How COTS move over long timeframes is a key determinant of model parameterization and at both local and regional scales. However, techniques for tracking COTS over appropriate timescales have not been available due to the lack of a tagging technique. Research in NESP 2.1.1 has overcome this problem allowing us to follow COTS potentially for periods of months and over the greater distances needed for parameter estimation. In NESP 3 these new techniques will be combined with acoustic telemetry to provide this key data.

3. Predators

A variety of analyses have now identified a link between zoning and COTS. These include green zones being less likely to experience outbreaks, green zones recovering more rapidly from COTS outbreaks, and green zones having fewer and smaller COTS (results from NESP 2.1.1). This suggests that predation pressure is greater in green zones because there are more, or more diverse predators, present. These effects could be brought about through direct effects on the predator communities or indirectly through effects on habitat structure. This work would test this by documenting COTS predation in the field using eDNA analysis on likely predators, and comparing the abundance of confirmed predators of different types on paired green and blue reefs.

4. BioControl and Genetic Modification

In the long-term COTS control must move beyond manual control to be viable. Currently the only broad-scale options on the horizon are the use of some form of biocontrol or the development of genetic technologies to moderate population dynamics during outbreaks. In this work we will review developments in biocontrol and the application of gene technologies to the management of pest species to provide managers with up-to-date information on the potential of these technologies for control, ensuring they are properly positioned to make decisions on their relevance to COTS management.

Alignment with NESP Research Priorities

Research Plan v1 Priority 1.1: Further development of a systematic approach to Crown-of-Thorns eradication. Identify and trial risk abatement, and prioritisation strategies in response to Crown of Thorns outbreaks, extreme events and biosecurity threats. Develop and implement a plan to reduce Crown-of-Thorn numbers by two million.

Project Keywords

Crown-of-thorns starfish; COTS; Integrated pest management; Great Barrier Reef; GBR; Resilience; Coral cover.

Project Funding

This project is jointly funded through CSIRO, JCU, UQ, GBRF, AIMS, QUT, USyd and the Australian Government’s National Environmental Science Programme.

Project Publications







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