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EXECUTIVE SUMMARY
Understanding the causes of crown-of-thorns starfish outbreaks is
critical to the effective management of the Great Barrier Reef Marine
Park. If managers are to control outbreaks on a large scale it can be
only through tackling the causes - not the symptoms. Indeed, knowing the
causes (in particular the role of human activities) will determine whether
or not management intervention is philosophically and ecologically appropriate.
Two main theories to explain crown-of-thorns starfish outbreaks remain popular and, as yet, unresolved. One of these relates to the possible
increase in food for larval starfish resulting from increases in nutrient
levels due to freshwater run-off from adjacent land masses. Logically,
the additional supply of food to starfish larvae would result in greater
survival either directly (if larvae are normally food-limited) or indirectly
by accelerating development rates. Research at the Australian Institute
of Marine Science is investigating these possibilities.
The substantial quantities of nutrients contained in terrestrial run-off
often lead to increases in phytoplankton - the primary food source of
larval crown-of-thorns starfish. While this occurs naturally as a result
of cyclones and torrential rain, modification of catchments and coastal
plains for agriculture and development could enhance the effects.
Crown-of-thorns starfish larvae appear to have alternative sources of
nutrition, in particular dissolved free amino acids (DFAA). Previous research
has shown that crown-of-thorns starfish larvae are rather exceptional
in their ability to take up DFAA. However, concentrations of amino acids
in coral reef waters under normal conditions are generally too low to
make significant contributions to the larval diet (if indeed DFAA is taken
up for nutritional purposes). Whether or not these background concentrations
changed seasonally, particularly in response to terrestrial run-off, was
unknown.
The project by Dr Tenshi Ayukai, Diane Miller and Lynn Swan monitored
the levels of DFAA over the crown-of-thorns starfish spawning period (when
larvae were most likely to be present) in an area of known increasing
populations of the starfish. A cyclone with localised torrential rainfalls
occurred in the area during the study.
The results of the study showed that DFAA concentrations were
not affected by terrestrial run-off. Throughout the starfish's spawning
season amino acid concentrations remained at levels where this potential
food source would not play a significant role in larval nutrition.
Further research into this theory of links between larval nutrition
and starfish outbreaks should concentrate on the dynamics of the primary
food source - phytoplankton.
THIS PUBLICATION IS CITED AS:
Ayukai, T., Miller, D., & Swann, L. (1996)
Dissolved free amino acid concentration: implications for COTS larval
nutrition.
CRC Reef Research Centre Ltd
Technical Report No. 9
Townsville; CRC Reef Research Centre Ltd, 30 pp.
ISBN 1 876054 08 5
A full copy of this report may be obtained from the author(s),
and through the following libraries:
Agency libraries: Great Barrier Reef Marine Park Authority,
Townsville; Australian Institute of Marine Science, Townsville; James
Cook University, Townsville; Queensland Department of Primary Industries and Fisheries
(Brisbane and regional offices); Queensland Department of Environment
and Heritage (Brisbane and regional offices); CSIRO Division of Marine
Research, Tasmania.
Public libraries: Queensland, New South Wales, Tasmania and South
Australia State libraries; National Library, ACT.
Parliamentary libraries: Queensland, New South Wales and South
Australia parliamentary libraries.
For a hard copy (or pdf file) of the report contact CRC Reef on info@crcreef.com.
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