A crown-of-thorns starfish (Acanthaster planci) control program at Grub Reef, central Great Barrier Reef

Brief description

A crown-of-thorns starfish control program was conducted on Grub Reef, a mid-shelf, lagoonal reef in the central Great Barrier Reef. The control site was located on the leeward, north-western side of the reef, in an area which previous surveys indicated had large numbers of starfish. The site covered an area of 0.64 km² and contained 53 patch reefs interspersed amongst a predominantly sandy substrate of 10-30 m depth. Each patch reef was mapped, marked and numbered for identification during the control exercise. Starfish control was carried out by 15 Royal Australian Navy divers between 3 and 17 July 1986. Each patch reef was searched by a squad of 5 divers, spaced about 5 m apart searching to a depth of 20 m. All starfish observed were injected with 5-10 ml of saturated copper sulphate solution using "Dupont" agricultural injection guns. Once injected, starfish were marked with a cut from a knife to avoid repeated injection. The final 2 days of the control exercise were used to inject starfish on adjacent patch reefs to the north and west of the control site. As a guide to the efficiency of the control exercise, starfish were injected on patch reef No.3 over the last 4 consecutive days of the control.Biological surveys were conducted 2 weeks prior to the start of the program (23-26 June 1986), and 1 month and 6 months after the program had ended (20-23 August 1986 and 20-22 January 1987). Three different methods were used during each of these surveys: (1) The perimeter of Grub Reef, including a group of patch reefs to the west of the main section of the reef, was surveyed using the manta tow technique. Counts of starfish and estimates of coral cover were recorded; (2) Twenty-six of the patch reefs were initially chosen randomly and then searched intensively by SCUBA divers during each of the 3 surveys. Two divers swam around the sides, and across the top of each patch reef, recording the number of starfish observed and estimating the relative cover of live and dead corals using the same categories as manta tow; (3) A 50 m line transect was laid along the crest of each of the 26 patch reefs, to estimate the relative cover of live and dead corals.A detailed record was kept of the cost of undertaking all various aspects of the control program. The total cost of the program was calculated by including the direct outlay recorded plus calculating shadow prices for the services provided by the Government. This study was undertaken to evaluate the effectiveness of a crown-of-thorns starfish (Acanthaster planci) control program at Grub Reef in the central Great Barrier Reef and to assess the biological benefits gained in the light of the costs of the program.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: The manta tow technique:This technique involves towing an observer at about 2 knots behind a small inflatable boat, stopping every 2 minutes to record the number of crown-of-thorns starfish observed and the relative cover of live and dead corals.Six categories were used for estimating coral cover:0 (0%)1 (1-10%)2 (11-30%)3 (31-50%)4 (51-75%)5 (76-100%). The technique is described in more detail in:Moran PJ, Johnson DB, Miller-Smith BA, Mundy CN, Bass DK, Davidson J, Miller IR, Thompson AA (1989) A guide to the AIMS manta tow technique. Australian Institute of Marine Science, Townsville.The method used to estimate relative cover of live and dead corals along 50 m transects is described in: DeVantier LM, Barnes GR, Daniel PA, Johnson DB (1985) Studies in the assessment of coral reef ecosystems: assessment protocol, vol 1. Australian Institute of Marine Science, Townsville.Program cost:As well as financing direct outlays for ship time, some transport and purchases of equipment and consumables required for the project, the Australian Government provided personnel: managers, scientists and Navy divers and air transport for the Navy divers.Actual salary rates and an estimate of overheads were used for the managers and scientists employed by the Australian Government. Shadow prices for diving labour were based on the cost of repeating the exercise utilizing commercial diving services, because it could not be assumed that Navy services will always be available and because Navy salaries would not reflect the full costs to the government of providing diving services. Prices were based on quotes obtained from commercial diving services. The cost of air transport of Navy Divers to the locality has not been included as the divers utilized a scheduled cargo service flight at no extra cost. All data are in 1986 prices.The following reference was used in carrying out the cost-benefit analysis:Mishan EJ (1978) Cost-benefit analysis. Allen and Unwin, London.

Notes

Credit
Johnson, David B, Mr (Principal Investigator)

Credit
Sweatman, Hugh PA, Dr (Custodian)