CRC REEF RESEARCH CENTRE TECHNICAL REPORT No. 25

Development Of Cost-Effective Control Strategies For Crown-Of-Thorns Starfish.

David A. Fisk, Reef Research & Information Services
Mary C. Power, Queensland Department of Environment & Heritage

FOREWORD

Control of Crown-of-thorns starfish has been an important issue for reef managers for over 30 years. There are no methods which can be applied to intense starfish populations affecting large areas of reefs but tactical controls to retain corals at sites important for tourism and recreation are feasible and often recommended.

Control programs involve a substantial commitment of trained effort over a long period. This report documents practical research which enables managers and planners of control programs to appreciate the scope, commitment and limitations of effective field operations. It is an important and practical management support document applicable to coral reef environments throughout the Indian and Pacific Oceans.

Richard Kenchington
Executive Director
Great Barrier Reef Marine Park Authority

EXECUTIVE SUMMARY

Crown of thorns (COTS) eradication effort was carried out by injection of Dry Acid (Sodium Bisulphate solution). Three injection regimes were tested at two different reefs (Lizard Island and Green Island) for their effectiveness in reducing COTS densities on small patch reefs. The effect on coral community structure of altering COTS densities was also investigated.

Key Results

1. Over a 10-month period at Lizard Island, two injection regimes (high frequency-low intensity, and low frequency-high intensity effort) significantly reduced COTS densities.

2. At Lizard Island, high frequency/low intensity effort was more effective over the longer term at reducing coral impacts than a low frequency/high intensity treatment. However, hard coral cover decreased at a steady rate in both treated and untreated sites. This was postulated to be due to the continual influx of COTS immigrants from elsewhere. In contrast, a standardised index of the amount of coral damage (complete and partial mortality), significantly increased in the untreated sites compared to the treated sites, indicating that the treatments were halting the expected decline in coral cover at these sites.

3. At Green Island, a similar high frequency/low intensity treatment regime and an additional high intensity treatment regime did not significantly reduce COTS densities. Unexpected factors prevented the analysis of impacts on the coral community as proposed. However, valuable descriptive assessments of impacts are presented in the appendices.

4. Migration of COTS into both Lizard and Green Island study sites was postulated to be negating the effect of protective measures over longer periods. Consequently, eradication procedures appeared to be stemming the rate of decline but not the net decline in coral cover.

5. Diver experience was also found to be an important factor in the effectiveness of a control program. Greater diver experience both with diving in general, and with finding cryptic COTS in particular, resulted in higher numbers of COTS injected per unit time.

Recommendations for Control Programs for Industry

Note: The following recommendations are based on results contained in this report and additional observations made during the study.

1. Successful control programs require : (1) constant eradication effort over relatively long periods of time; (2) maintenance of the focus on the target area and avoidance of the inclination to apply effort on higher concentrations of COTS outside the target area; (3) treating COTS concentrations in off-site areas in a strategic manner if there is potential for migration into the target area; (4) maintenance of medium term vigilance of the local situation (in terms of years), until the threat is passed; and, (5) ensuring that the ability to alter the intensity of eradication efforts at short notice is retained.

2. It is essential to have knowledge of the COTS outbreak situation beyond the boundaries of the desired area of protection because migration of COTS from adjacent areas will dictate the type and amount of eradication effort.

3. The interval between eradication visits at any site should be determined on a case by case basis. The required degree of eradication effort is a function of the unique situation associated with each area of reef requiring protection, and no single strategy will be applicable in all outbreak situations or reefs, or at all phases of an outbreak on one reef.

4. However, as a starting point, it is recommended that an intensive eradication effort in the initial phases of a control program be followed by frequent less intensive effort and that only well trained competent divers are used.

In trials of eradication programs with different levels of intensity using Dry Acid (sodium bisulfate solution), the study found that at one site, high frequency/low intensity efforts were more effective than low frequency/high intensity efforts at reducing the effects of starfish on coral cover. However, eradication efforts at two sites could not halt a decline in coral cover, mainly because large numbers of starfish moved into the control sites from the large populations on other parts of the reef.

THIS PUBLICATION IS CITED AS:
Fisk, D.A. & Power, M.C. (1999)
Development of Cost-Effective Control Strategies for Crown-of-thorns starfish.
CRC Reef Research Centre Ltd
Technical Report No. 25
Townsville; CRC Reef Research Centre Ltd, 61 pp.

ISBN 1 876054 99 9

A full copy of this report may be obtained from the author(s), and through the following libraries: