Crown-of-thorns starfish: surveillance and life history

Dave Westcott
Led by: Dr David Westcott, CSIRO


Project Summary

This project supports the implementation of the NESP Crown-of-Thorns Starfish Integrated Pest Management Project’s management and research strategy by i) describing ecological parameters key to parameterizing the tools underpinning the management strategy, ii) analysing existing data sets to assess management performance and describe the interaction between CoTS and bleaching, and, iii) scoping new technologies and surveillance strategies for detecting and monitoring primary and secondary outbreaks. The work will involve a combination of field ecological research, statistical analysis of existing data, technology and strategy development (the latter through workshops) and inform decision making through incorporation into decision support tools and recommendations.

Project Description

This project will address a number of knowledge or technological gaps that are central to the development of strategies and tools for management of CoTS on the GBR.

The first of these gaps is that the cost and logistical difficulties associated with conducting field work on CoTS at the scales appropriate for many of the research questions that are fundamental to successful management vastly outstrips the funding available. These questions include i) documenting the interaction between CoTS, bleaching, and management, ii) documenting the relationship between the distribution of coral condition, coral communities, and CoTS, and, iii) assessment of the performance of the control program and the factors that influence this.  Questions such as these can, however, be addressed through analysis of the existing datasets produced as part of current field operations, including both the CoTS Control Program and the Field Management Program. While both these data sets were established, and have been contributed to since 2012, they have not previously been accessible or curated for researchers.

In this work we will clean and prepare the Control and Field Management Program data sets for research use. We will seek access to additional datasets from our partner institutions, eg. 2016 and 2017 coral bleaching data data (AIMS/GBRMPA/JCU), to address the questions identified above. As the work progresses, additional questions will be identified and these will be addressed where resources permit.

The second knowledge gap relates to two areas of CoTS ecology where the information cannot be gleaned from existing sources. First, we have only limited information on aspects of CoTS ecology that are central to i) parameterizing the models that underpin the decision support tools that underpin the implementation of the CoTS Integrated Pest Management strategy, and, ii) to designing management that responds to the distribution of CoTS outbreaks. Specifically, information on the key life history parameters such, e.g. age specific recruitment rates, is required to parameterise the population growth models which are fundamental to both the local and regional decision support tools. Second, predation remains one of the most likely hypothesised influences on CoTS population dynamics and this is supported by data from the LTMP (Sweatman 2008; Vanhatalo, Hosack & Sweatman 2016) and FMP and control programs (Westcott, in prep). Manipulation of predation is also one of the few broad-scale management levers currently available.

Filling these gaps requires field work. To describe population parameters we will use repeat surveys of individual sites, and if feasible mark-capture-recapture methods, across years at Blue and Green zone sites to document population structure and individual life-stage transition probabilities. To describe the suite of predators feeding on CoTS we will implement faecal DNA sampling methods developed in NESP RvP3 to survey the fish community at reefs in the current outbreak zone.

The third gap is a technological gap.  We currently have no means of detecting new (or 1°) outbreaks, or of efficiently monitoring the movement of existing (or 2°) outbreaks, beyond ad hoc observations and the limited surveying conducted under GBRMPA’s Field Management Program.  This is a major issue as it means that a timely response to new outbreaks is subject to chance reporting, greatly reducing the probability of successful and early control being achieved and leaving us in the current situation where outbreaks are already well established and wide-spread before we are aware of their existence. Similarly, our ability to delimit existing outbreaks, and to most effectively focus our management effort, is severely compromised. Ultimately, any CoTS control program will require the capability to i) predict and detect new (or 1°) outbreaks, and, ii) monitor the spread of existing (or 2°) outbreaks if it is to be efficient and successful. The question is, what tools should be used and how should these tools be deployed?

It is currently unclear what drivers cause 1° outbreaks which makes identification of appropriate drivers to monitor difficult. Current hypotheses point to a suite of potential drivers (e.g., including sea temperature, flood events, current strengths, nutrients, algae densities, and predator loss). Some of these are amenable to either remote or automated monitoring while others require dedicated field monitoring. In the absence of certainty about which drivers are responsible a logical approach is to monitor as many of the candidate drivers as possible while simultaneously monitoring larval production and to do so on a regular basis across the hypothesised initiation box. This approach allows i) detection of hypothesised outbreak conditions, ii) timely detection of and response to 1° outbreaks, iii) testing and development of hypotheses for outbreaks. In contrast, responding appropriately to 2° outbreaks requires documenting the distribution and pattern of spread of CoTS and their larvae. We currently rely on divers for this information, which limits the coverage and responsiveness of the surveillance.

We envisage that a cost-effective approach to both 1° and 2° monitoring might be based on a combination of remote sensing data and (semi-) automated water sampling conducted on-board during research, management and tourism activities on the reef to provide real-time, spatial sampling of outbreaks and outbreak pre-conditions. This could include CoTS detection using the eDNA technologies developed by Uthicke and Doyle (AIMS) and being refined as part of NESP RPv3. In this work we would:

i) Scope and design a monitoring program based on hypotheses for outbreaks, operational constraints and system ecology in an expert workshop.
ii) Outline a pathway for the implementation of monitoring.
iii) Refine detection technologies and identify the pathway to operationalising these.

The final knowledge gap relates to identifying and describing the distribution and health of coral communities. This is an important step as it allows us to identify and prioritise the assets we seek to protect.  In this work we will contribute capacity to support Mumby et al.’s Project 4.5. By linking these two projects we will be able to contribute information and resources to mutual benefit. With spatially explicit information of this kind it becomes possible to include coral health, e.g. bleaching status or overall resilience, in the estimation of control strategies. In this component of the work, we will collaborate with Mumby et al. to ensure that their Resilience Based Management Guidance tool and the Regional Decision Support Tool are complementary and able to swap data and outputs.

The results of each of these sub-projects will be communicated in variety of means. First, data products will be incorporated into the decision support tools that are currently being trialled with managers. As these tools mature and are refined they will be guiding policy and operational decisions made by managers and the control program. Results will also be shared directly with managers and the control program during the Project’s CoTS Working Group Meetings and the CoTS Advisory Team meetings. Results will be communicated more broadly during public and scientific presentations, reports and papers.

NESP 2017 Research Priority Alignment

NESP Priority Theme 1.1 – Further development of a systematic approach to crown of thorns control.

Project Keywords

Crown-of-thorns starfish; CoTS; Predation; Life-history; Surveillance.

Project Funding

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

Project Publications






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