Invasive Pest Control

Advancing Corallivore Mitigation: Evaluating the Potential of ROV Technology for Crown-of-Thorns Starfish (Acanthaster spp.) Control on the Great Barrier Reef

 

 

Introduction and Context

 

The Crown-of-Thorns Starfish (COTS), Acanthaster planci, has represented a significant and recurrent threat to the Great Barrier Reef (GBR) ecosystem since the 1960s. These large corallivores cause extensive and rapid degradation of coral cover, dramatically reducing both coral and general reef biodiversity [1, 2]. According to the Australian Institute of Marine Science (AIMS), COTS outbreaks—where densities exceed 30 starfish per hectare, double the number that can cause severe reef damage—are a leading cause of coral decline [4]. The GBR's immense social, economic, and icon value is estimated in the billions ,[3], making effective mitigation of COTS outbreaks a national and global priority.

Over the past three decades, control programs, largely funded by government grants through bodies like the Great Barrier Reef Marine Park Authority (GBRMPA) and the Reef Trust, have aimed to mitigate these impacts. However, the efficacy, efficiency, and fragmented nature of these programs—as evidenced by the recurrent nature of the outbreaks and observed funding delays—have led to frequent debate regarding the strategies currently employed.

 

Limitations of Current Diver-Based Control Methods

 

Current COTS control primarily relies on manual removal or single-shot lethal injection performed by trained divers. This method, while successful in localised reduction of COTS populations, is inherently challenged by logistical and safety factors:

 

Operational and Safety Constraints

Constraint                                    Impact of Control Efficacy

Diver Health and Safety.            Divers are prone to decompression sickness and are exposed to environmental                                                                 hazards (hostile marine life, poor visibility, strong currents, COTS spines)

"Bottom Time" Limits                 Occupational Health and Safety (OH&S) regulations historically restrict divers to                                                                approximately 40 minutes of bottom time, four times per day}}$ [cited in 11].

Starfish Behaviour                      COTS are cryptic and more active at night, while most culling programs operate                                                                during the day, reducing effectiveness.

Environmental Stressors           Control programs require multiple support vessels, leading to high fuel consumption                                                        and potential localised environmental disturbance.

Economic and Efficiency Inefficiencies

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1. High Cost per Starfish: According to figures cited by Dr. Roger Beeden from the GBRMPA in 2023, 320,000 \text{ starfish were culled over43,000 diver hours at an estimated hourly cost of $953.This equates to only 7 starfish killed per hour, or a staggering $136 per starfish [7].

2. Low Culling Rate: Independent GBRMPA data from 2023–2024 further suggests a culling rate of approximately one starfish every 20 minutes (50,227 COTS culled in 16,657 hours) [12], underscoring the low return on labor investment.

3. Fragmented Efforts: Control often relies on short-term funding cycles, leading to inconsistent efforts, duplication across multiple stakeholders, and the potential for a disincentive to permanent solutions among organizations dependent on the income stream.

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The Potential of Remotely Operated Vehicles (ROV)

 

Technological advancements in underwater robotics offer a clear path to supplement and optimise existing control efforts.

 

Autonomous and Non-Autonomous Robotics

 

Pioneering efforts in ROV development demonstrate the potential for a "game-changer" in COTS management:

• COTSbot / RangerBot (QUT): The Queensland University of Technology (QUT) developed the COTSbot for autonomous COTS detection and injection, later evolving into the RangerBot. This autonomous platform was designed to deliver over 200 lethal shots per 8-hour shift [8] and achieved a 99.4\% \accuracy rate in COTS detection[9]. However, despite these technical successes, widespread deployment and field documentation of autonomous COTS injection has not been publicised since 2018 [9, 10].

 

The Emergence of Cost-Effective, Non-Autonomous Solutions (Down Deep Drones)

 

New solutions leveraging accessible, off-the-shelf robotics offer a more immediate, budget-friendly deployment pathway:

• Proprietary ROV Tooling: Australian firm Down Deep Drones has developed a non-autonomous COTS injector prototype mounted on a highly reliable, off-the-shelf ROV platform (e.g., QYSEA).

• Efficiency Projections: The system aims for a culling rate of one injection every two minutes in high-density areas, representing a significant increase over the current diver rate of one starfish every 20 minutes.

• Operational Advantage:

  • Continuous Operation: Surface-powered ROVs (starting from$12,000 AUD)allow for continuous COTS injections, overcoming diver bottom-time limits.

  • Accessibility: As a simple-to-operate, low-cost system (under $5,000 for the prototype unit and injector), it is easily accessible to researchers, environmental stewards, and citizen scientists after minimal training (1–2 hours).

 

Challenges to Innovation and Future Pathways

 

 

Historical Impediments to ROV Trials

 

The integration of innovative ROV technology into GBRMPA management has been historically problematic.

• Oakford Offshore (2016 Trial): An early field test of a modified ROV injection system was arguably compromised by operational conflicts of interest: the low funding received by Oakford offshore necessitated the use of the vessel and personnel of a diving contractor (Venus II used by AMPTO). The trial area provided had minimal COTS, suggesting the test may have functioned as a monitoring check on a previous cull rather than an impartial assessment of the ROV's culling capacity [10A, 10B].

• Down Deep Drones (2018/2024 Outreach): Direct offers to GBRMPA and affiliated research institutions to donate and demonstrate a cost-effective ROV injector prototype were met with no substantive response, highlighting a systemic difficulty in integrating unsolicited, potentially disruptive technology.

 

Conclusion and Call for International Validation

 

The resource scarcity currently limiting COTS control—"the scale of COTS outbreaks on reefs across the GBR far exceeds the resources that are available" [11]—demands the adoption of supplementary, high-efficiency tools.

The advantages of ROV-enabled control are clear: lower operational cost, freedom from human physiological and safety limits, and high-fidelity 4K data collection (e.g., via towed surveys and real-time streaming).

The continued bureaucratic reluctance to sanction controlled, impartial field trials on the GBR necessitates a strategic pivot. By seeking validation in collaborative jurisdictions, such as Thailand's highly receptive marine conservation community, new ROV technology can demonstrate its potential to provide a scalable and sustainable solution to this persistent environmental challenge, ultimately contributing valuable data and methodologies back to the global reef management community.

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References

[1] DCCEEW (Department of Climate Change, Energy, the Environment and Water). (n.d.). Crown-of-thorns starfish control program: Great Barrier Reef. Retrieved from https://www.dcceew.gov.au/parks-heritage/great-barrier-reef/case-studies/crown-of-thorns/

[2] AIMS (Australian Institute of Marine Science). (n.d.). Causes of crown-of-thorns starfish outbreaks. Retrieved from https://www.aims.gov.au/research-topics/environmental-issues/crown-thorns-starfish/causes-crown-thorns-starfish-outbreaks

[3] Great Barrier Reef Foundation. (n.d.). The value of the Great Barrier Reef. Retrieved from https://www.barrierreef.org/the-reef/the-value

[4] The Nature Conservancy. (2003). Crown-of-thorns starfish (COTS) management. Retrieved from https://www.reefresilience.org/pdf/COTS_Nov2003.pdf

[5] Grimm, V., & Berger, U. (2023). Analyzing and Modeling the Dynamic Response of Marine Ecosystems to Environmental Change. Environmental Modelling & Software, 166, 105429. Retrieved from https://www.sciencedirect.com/science/article/pii/S0304380023001746

[6] Pratchett, M. S., Caballes, C. F., Rivera-Posada, J. A., & Sweatman, H. P. A. (2014). Limits to understanding and managing outbreaks of crown-of-thorns starfish (Acanthaster spp.). Oceanography and Marine Biology, 52, 133-200. doi:10.1201/b17143-4

[7] Readfearn, G. (2022, February 13). Australia is spending billions on the Great Barrier Reef – will it do any good? The Guardian. Retrieved from https://www.theguardian.com/environment/2022/feb/13/australia-is-spending-billions-on-the-great-barrier-reef-will-it-do-any-good

[8] “RangerBot: An Autonomous Underwater Robot for COTS Control.” Queensland University of Technology. https://research.qut.edu.au/qcr/Projects/cotsbot-eliminating-invasive-reef-species/ , accessed 23 July, 2024. QUT.

[9] Queensland University of Technology. (n.d.). RangerBot: Environmental monitoring using robot vision. Retrieved from https://research.qut.edu.au/qcr/Projects/rangerbot

[10] Queensland University of Technology. (n.d.). COTSbot: Eliminating invasive reef species. Retrieved from https://research.qut.edu.au/qcr/Projects/cotsbot-eliminating-invasive-reef-species/

[10A] COTS Culling ROV Field Test. (2014). Atlas of Living Australia. https://fieldcapture.ala.org.au/project/index/d9a27e47-9277-4609-8c11-ce95803373ed

[11] Fletcher C. S., Bonin M. C, Westcott D. A. (2020). An ecologically-based operational strategy for COTS Control. Reef and Rainforest Research Centre Limited NESP Tropical Water Quality Hub. Retrieved from https://nesptropical.edu.au/wp-content/uploads/2020/04/NESP-TWQ-Project-3.1.1-Technical-Report-2.pdf

[12] Great Barrier Reef Marine Park Authority. (n.d.). Crown-of-thorns starfish control program. Retrieved from https://www2.gbrmpa.gov.au/our-work/programs-and-projects/crown-thorns-starfish/Crown-of-thorns-starfish-control-program

[13] Biopixel. (n.d.). COTSbot: Robo reef protector to save the reef from the crown-of-thorns starfish. Retrieved from https://biopixel.tv/cotsbot-robo-reef-protector-to-save-the-reef-from-the-crown-of-thorns-starfish/

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