Acanthaster planci - Management Information
Compiled by IUCN SSC Invasive Species Specialist Group (ISSG)
It is important to first determine whether the starfish population is at normal levels or
can be considered to be outbreaking. "Normal" densities of A. planci are considered to
be in the range of between 1 and 15 per hectare, depending on the amount of coral
cover available. It is not recommended that the starfish be controlled when occurring
at this level, as damage to corals can be sustained with no obvious long-term damage
when the starfish occur at low densities (Lassig, 1995). The difference between
"normal" and outbreaking populations should be obvious, often involving up to a 10fold increase in starfish numbers. The policy of the Great Barrier Reef Marine Park
Authority is that control of A. planci should be limited to small-scale measures in
areas important to tourism or science, unless it can be proven that the outbreak was
caused or exacerbated by human activity (Lassig, 1995).
The Great Barrier Reef Marine Protection Authority recommend that any control
programmes be carried out a realistic scale (up to 2-4 ha), have adequate funding, and
be initiated as soon as possible after the outbreak has been detected. Control
programmes are rarely one-off operations, with starfish often moving into the cleared
areas, hence it is necessary for there to be long-term commitment to the programme
(Lassig, 1995).
Control programs in Micronesia and the Great Barrier Reef have involved the killing
of up to 350 000 individual starfish, but in many cases it is believed that the
population of A. planci would have decreased in size anyway without a control
program (Birkeland and Lucus 1990). Approximately 15 million starfish have been
killed in control programs throughout the last 15 years in the Indo-Pacific region
(Moran, 1997). By far the largest of these programs was undertaken in the Ryukyu
Islands (Japan) where almost 13 million starfish were removed from the reefs in that
region (Moran 1997). Despite this intensive Japanese effort (costing approximately
A$6 million) the control program was regarded to have been unsuccessful in either
eradicating the coral-feeding starfish or preventing further coral mortality. One of the
greatest obstacles to any control project for A. planci has been the delay to initiate
control before significant damage to coral ecosystems occurred (Birkeland and Lucus
1990). Arranging volunteers, bad weather and funding availability can all delay
control commencement (Birkeland and Lucus 1990). Research into accurate
predictions of when and where A. planci outbreaks will occur are essential to improve
future control and increase the chances of success (Birkeland and Lucus 1990). For
example, a hydrodynamics study found that due to the interaction of tidal, gravity and
wind flows, some areas within the reef retained higher numbers of larvae than others.
Surveillance of these locations, which may be correlated with initial recruitment of A.
planci, could provide an 'early warning' strategy for monitoring and controlling future
outbreaks of this starfish on reefs (Black and Moran 1991).
In general there is substantial research and information on both ecological and
management-based aspects of the coral-feeding starfish and its control. For example,
since late 1985 the Australian Federal Government has provided about $A2.5 million
for research; the Australian Institute of Marine Science and the Great Barrier Reef
Marine Park Authority also have also supported the effort (Moran 1997). As of 1997,
about 70 scientists throughout Australia were collaborating on about 58 different
projects. Topics of research include: larval dispersal, developing monoclonal
antibodies for A. planci to identify them from other starfish larvae in samples;
determining coral reef and fish recovery rates after outbreaks, use of satellite
photography to investigate the effects of starfish outbreaks, developing mathematical
models to understand starfish outbreaks, determining the efficacy of starfish control,
investigating potential biological control options, undertaking a risk analysis of the
starfish and investigating starfish predation (Moran 1997). The main long term
objective of research in Australia is to determine the cause(s) of outbreaks.
Research is not limited to Australia, however. Recently, scientists from Japan have
identified a feeding attractant for this starfish derived from the viscera of the sea
urchin (Toxopneustes pileolus). Arrachidonic acid and alpha-linolenic acid (both
unsaturated fatty acids) are found to have biological activity and it is anticipated that
these attractants could be used to control A. planci (Teruya et al. 2001).
The best general management policy according to the Palau Conservation Society
(1999) is not to interfere with outbreaks unless the areas are small and of special value
such as a tourist or heritage site. Visual searches for starfish infestations using speed
boats are a useful tool for locating A. planci aggregations (Crown of thorns starfish
clean-up 2002). Hand-harvesting is the only widespread method used to date and is
only feasible for protecting small areas - large scale control is not known (Birkeland
and Lucus 1990). An estimated 1% of starfish will regenerate from fragments, which
means cutting the starfish and dumping them back on the reef is a viable control
option (Birkeland and Lucus 1990). This method is better than using chemicals,
which foul the reef and are potentially harmful to humans (Birkeland and Lucus
1990). Alternatively the starfish may be removed from the reed and disposed of by
dumping on land; however, this removes nutrients from the reef ecosystem and
increases soil salinity at dumping sites (Birkeland and Lucus 1990). Chemical
treatment of starfish with lethal compounds eliminates the disposal problem and is
more efficient, with 100+ starfish injected per person per hour (Birkeland and Lucus
1990). The following toxins have been used successfully for killing the coral-feeding
starfish: sodium bisulphate (Palau Conservation Society 1999), 25ml concentrated
formalin, 15ml concentrated ammonia, 10ml 16% hydrochloric acid (HCl) and 10ml
saturated copper sulphate (CuSO4) (Birkeland and Lucus 1990). Copper sulfate is the
cheapest option, however, it is known to be toxic to some marine animals and there is
concern about its unwanted effects on the coral-reef ecosystem (Birkeland and Lucus
1990). Harriott et al. (2003) and Lassig (1995) recommend sodium bisulfate as the
safest and most effective toxin, although it is extremely costly.
Control teams may consist of bounty collectors, volunteers and/or employed control
teams. As the spines of this starfish are poisonous care should be taken when reef
walking (Moran 1997). Bounties are usually at the rate of $US.10 to $.20 per starfish,
while the costs for employing a control team is significantly higher (Birkeland and
Lucus 1990). For example, the bounty system was used in the Ryukyus, Japan, and
cost 0.18 per starfish, whereas a control team used at Shikoku, Japan, cost $US16.29
per starfish (Birkeland and Lucus 1990). Bounty systems have also been used with
success in American Samoa and Palau, but have failed in Guam, Saipan, Tinian and
Rota - probably due to the inaccessibility of the areas of starfish infestation (Birkeland
and Lucus 1990). Starfish need to be accessible to snorkellers and waders and there
needs to be easy access to the site by car if the bounty system is to work (Birkeland
and Lucus 1990). Sites that need to be accessed by scuba diving or other specialised
means will not be suitable (Birkeland and Lucus 1990). Another limitation of the
bounty method is that bounty hunters tend to focus on making a profit rather than
controlling the starfish so they move from one dense aggregation to another leaving
behind them a thin dispersal of starfish released from the competitive pressures of
other starfish (Birkeland and Lucus 1990). A possible solution to this would be to
combine the efforts of both bounty hunters with a control team whose job it would be
to scour the area afterwards picking up the individual starfish which the bounty
hunters had missed. An alternative option would be to educate the hunters on the
importance of collecting, if possible, every last individual from a site in order to
reduce future damage to coral colonies. Thirdly, the initial bounty price could be
increased for the few remaining individuals at a site to encourage bounty hunters to
collect them.
Lastly, the effect of increased run-off from human terrestrial systems into rivers and
then into the sea and associated reef ecosystems has been implicated with
eutrophication (algal growth) (Brodie et al. 2005; Bell 1992). This could well be a
principal causative factor of coral-feeding starfish outbreaks (Bell 1992). Therefore,
in areas of the Great Barrier Reef where elevated levels of nutrients and algal growth
exist, special precautions need to be exercised in the control of sewage effluents and
run-off in the vicinity of coral reefs (Bell 1992). Such management policies should be
applied elsewhere in the world where fragile coral systems exist.
Harriott et al. (2003) discuss three current theories as to what causes A. planci
outbreaks. They are: (1) Population fluctuations are a natural phenomenon, (2)
Removal of natural predators of the starfish has allowed populations to expand, and
(3) Human factors such as increased nutrient run-off (mentioned above) have caused
an increase in the planktonic food available to the starfish larvae, hence increased
numbers of adult starfish. Fraser et al. (2000) provide a guide to best management
practices in the control of A. planci.