Reef Research: Volume 6 No. 3 September 1996

Udo Engelhardt

COTS in Panama

eef scientists from around the world are breathing a collective sigh of relief. The Olympic Games of Coral Reef Science, or as they are more commonly known, the International Coral Reef Symposium, are again behind us. Some 1400 delegates recently converged on Panama City in Central America to present and discuss the very latest in reef research. Yes, you've guessed it, the crown-of-thorns starfish (COTS) issue was one of the many hotly debated topics. As it turned out, COTS was one of the eleven (!) concurrent sessions on the first day of the symposium. Interestingly, the organisers had lumped it into a mini symposium entitled `Pest Organisms' (I sometimes wish that people were a little bit more open minded!). Anyway, we had some very interesting presentations on COTS, followed by, at times, heated discussion. It was great to see that COTS can still get the adrenalin pumping. To give you a bit of a feel for the variety of research that was reported on, I have listed the available abstracts of all papers that were dealing with COTS. Happy reading.

Food limitation in the growth and development
of crown-of-thorns starfish larvae in the Great Barrier Reef

T. Ayukai ¹, K. Okaji ¹ and J.S. Lucas ²
¹ Australian Institute of Marine Science, PMB No. 3, Townsville MC Qld 4810
² Department of Zoology, James Cook University, Townsville Qld 4811

A carbon budget model was developed based on existing data of metabolic rates and uptake kinetics for phytoplankton (>2 µm), and dissolved free amino acids (DFAA) - two important food sources for the larvae of COTS. The model, in conjunction with three years of data on the ambient concentrations of these food sources in the Great Barrier Reef, suggest that COTS larvae are unable to meet even half their basal metabolic requirements in both reef and inter-reefal waters. Comparison of results from semi-natural rearing experiments with the field data also suggests that the growth and development of COTS larvae are usually food-limited, but the extent is not as severe as the model predicts. In detail, the critical food concentration for COTS larvae to achieve their optimal growth and development was in the range between 0.5 and 0.8 µg chlorophyll L^-1(as an overall measure for ambient food environments). Chlorophyll concentrations of this level do not commonly occur in the Great Barrier Reef.

Crown-of-thorns starfish controls: New techniques and strategies

U. Engelhardt and B.R. Lassig
Great Barrier Reef Marine Park Authority, PO Box 1379, Townsville Qld 4810

Previous research demonstrated that injection of individual COTS with saturated copper sulphate solution was the most cost- effective technique available for local COTS control operations. Concerns over the environmental toxicity of copper sulphate led to trials of alternative chemicals that were effective, cheap, safe to use and environmentally friendly. A commonly available swimming pool chemical (Dry Acid or sodium bisulphate) met all of these criteria and is currently being used in localised COTS control operations on the Great Barrier Reef. Current research is aimed at identifying the most cost-effective strategy for applying this technique.

Crown-of-thorns starfish outbreaks in the northern Great Barrier Reef

U. Engelhardt and B.R. Lassig
Great Barrier Reef Marine Park Authority, PO Box 1379, Townsville Qld 4810

Twice in the last 35 years COTS outbreaks originated in the northern Great Barrier Reef and subsequently spread southwards to affect a significant proportion of the 2900 reefs comprising the Great Barrier Reef. The exact geographical origin, the scale and the mechanisms responsible for the development of the outbreaks are largely unknown. Intensive surveys of 24 reefs in the area were initiated following reports of increasing COTS numbers. In 1994-95 nearly half of the reefs surveyed were classified as having active or incipient outbreaks on reef or local scales. Analysis of the survey results, in combination with population dynamic studies, suggests that the outbreaks developed simultaneously on reefs spread over at least two degrees of latitude as a result of several `good' years of recruitment. More widespread outbreaks appear likely.

Acanthaster plagues: Real or social constructs?

J. Sapp
Department of Science Studies, Atkinson College,
York University, 4700 Keele Street, North York,
Ontario, M3J 1P3, Canada

The history of the controversy surrounding Acanthaster planci outbreaks illustrates the difficulties of distinguishing between anthropogenic disturbance and natural fluctuations. The view that the outbreaks were new and therefore anthropogenically-caused competed with a view that large aggregations were natural phenomena and that their discovery as a 'plague' was merely a socio- technical construct due to the rise of environmentalism and the use of a new technology: SCUBA. Divergent ecological concepts regarding the stability and fragility of coral reef communities also underlay divergent views about the cause and cure for the outbreaks. The political nature of the debates further helped to polarize positions into two extremes: anthropogenic cause and necessary control measures versus natural cycles and no controls.

Commercial fishes as predators of adult Acanthaster planci

H. Sweatman
Department of Marine Biology, James Cook University Qld 4811
(now at Australian Institute of Marine Science, PMB No. 3, Townsville MC Qld 4810)

One theory of the causes of recent Acanthaster planci outbreaks is that human activity has reduced predation pressure on the starfish; in particular, that intense fishing has reduced the population levels of fishes that prey on A. planci. While small juvenile starfish are logically more vulnerable, the only documented cases of predation by commercially exploited fishes involve adult starfish. I examined the gut contents of 98 Lethrinus spp. caught within 500 m of high densities of adult A. planci in the southern Great Barrier Reef. None contained any A. planci remains but the size of the sample means that significant rates of predation cannot be excluded on statistical grounds.
COTSWATCH
Here, as usual, are the latest vital statistics for the COTSWATCH Reef-user scheme for the period from 1 May to 12 August 1996. Well, these valuable sighting reports just keep coming in at a nice steady rate. For the above period, the COTS program received 167 completed survey forms presenting information on 242 individual sites on some 93 different reefs from throughout the Marine Park. According to these reports, the main focus of both starfish activity and COTSWATCH reporting remains in the Cairns Section, with most records coming from some of the more heavily frequented mid-shelf reefs between Cooktown and Innisfail.

Many thanks to all the new and/or regular COTSWATCHERS out there for continuing to supply important and valuable updates on recent COTS developments in 'their' parts of the Reef.

Valued contributors for the period from May to August 1996:
A Hollis / DoE Heron Island; A Van Welderen / Cairns; C Purdon / QDoE Townsville; C Schonberg / AIMS, Townsville; C Williams / QDoE Cairns; Anonymous staff on Coral Princess Cruises; D Robb / Dingo Beach; D Wang / Baltimore USA; D Wiseman / Brinsmead; DA & BA Breen / Townsville; F Chapman / QDoE Pallarenda; G LaPraik / QDoE Cairns; G Wetstead / Cairns; H Malcolm / QDoE Pallarenda; I Stapleton / Nimrod, Cairns; IR Fleetwood / Gladstone; J Purcell, B Jewel, D Blackshaw, J Wells, O Schapendonk, R Aiello, R Schutte, R Westaway & S Woodford (all Great Adventures Cruises / Cairns); J Wright / Culburra; Jim Thompson / Airlie Beach; Kai Hoppe / Kiel GERMANY; M Abela / Pure Pleasure Cruises; M Allen / F.V. Seafari Cairns; M Burnham / QDoE Lucinda; M Ford / QDoE Lucinda; M Short / QDoE Cairns; M Smith / Moonlighting II Cruises, Trinity Beach; M Wilson / Whitsunday All Over, Airlie Beach; P Heatherwick / Port Douglas; R Tan / SINGAPORE; R Toff / Cairns; S Goodhew / Cairns; S Moon / Ocean Spirit Cruises, Cairns; S Richards / Captain Cook Cruises, Cairns; W Legg / Rockhampton; W Mahon / Clifton Beach.

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Great Barrier Reef Marine Park Authority
PO Box 1379 TOWNSVILLE QLD 4810. Phone: (077) 500 700, Fax: (077) 726 093
E-mail: registry@gbrmpa.gov.au