 | INDEPENDENT COTSREC PROGRAM REVIEW |
'The goals of the Great Barrier Reef Marine Park Authority's (GBRMPA) crown-of-thorns starfish research program are to understand more fully the causes of crown-of-thorns starfish outbreaks, to provide public forewarning of, and education concerning, outbreaks and to provide advice on appropriate control procedures where required. COTSREC provides independent expert advice to the GBRMPA on the running and directions of the research program.
'The GBRMPA/COTSREC program has operated in a highly efficient and productive manner during 1992-95 within the limits imposed by inadequate and uncertain funding. It has contributed significantly to the knowledge required for the use and enjoyment of the Great Barrier Reef in an ecologically sustainable manner. COTSREC has also significantly improved its communication with the public, the media and the tourism industry as well as its program for controlling COTS outbreaks on priority reefs.
'COTS outbreaks present invaluable research opportunities that are unavailable at other times. They also require expanded communication with the public and the media, as well as starfish control activities on priority reefs. Lags in funding during both previous outbreaks significantly constrained GBRMPA's ability to respond to these challenges and to capitalise on the vital opportunities outbreaks provide for obtaining a better scientific understanding of the phenomenon and its cause(s).'
Seek supplementary funding to enhance the program's abilities to carry out communication and research activities during the current outbreak.
Expand research on the effects of COTS on the population characteristics of massive corals to answer some important and worrisome questions concerning the future of these corals in the event
that outbreaks continue to occur at roughly 15-year intervals.
Initiate studies into pre-settlement factors relating to COTS outbreaks using field applications suitable for studying COTS larvae in the plankton. Studies of this nature may assist to identify outbreaks earlier and link larval dispersion and recruitment with hydrodynamic factors.
Support valuable research that can only be pursued effectively during outbreaks such as studies of predation on small juvenile starfish, movements of adult starfish populations and mechanisms for the ultimate termination of outbreaks.
Make available funds for additional fine-scale monitoring north and south of the Cairns Section in order to track the apparently expanding area of the outbreak.
Seek means of reinstituting multi-year guaranteed budget arrangements, such as those operating during the period of 1989-1992.
Obtain a contingency fund to be able
to respond fully to the scientific opportunities and communication and control responsibilities that new outbreaks create.
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| CAIRNS SECTION REVIEWS |
n examination of the geomorphology and related factors in the Cairns Section of the Great Barrier Reef Marine Park suggests that there are many features which would favour a pattern of outbreaks of crown-of-thorns starfish similar to that recorded. This is a part of the Great Barrier Reef in which mainland influence is probably greatest. The reef is adjacent to a mainland of high relief and high rainfall with the reefs in close proximity to this mainland. These effects would be aggravated by human activities which extend at least half way up the Cairns Section. In this area, there is also a high density of population and extensive agriculture, utilising practices which may lead to accelerated soil erosion and the possibility of nutrient flux from the mainland to the Reef lagoon. Further, the influence of the El Niño-Southern Oscillation (ENSO) phenomenon with periods of low rainfall interspersed with periods of flood with a 10-14 year cycle is likely to create a pulsatory temporal pattern which may also be related to crown-of-thorns starfish outbreaks.
The following features appear to coincide within the area that has been regarded as that from which crown-of-thorns starfish originate:
The southernmost extent of narrow shelf width,
The southernmost extent of the reef being close to the mainland and all its influences,
The southernmost extent of extensive Halimeda banks,
The southernmost extent of domination by crescentic reefs, and
The southernmost extent of ribbon reefs and low wooded islands.
The northernmost extent of dominance by crescentic reefs,
The northernmost extent of high rainfall on the adjacent mainland,
The northernmost extent of coastal ranges exceeding 1000 metres in height,
The northernmost extent of dense and long settled human populations,
The northernmost extent of extensive agricultural areas, and
The northernmost extent of dead, submerged shelf edge reefs.
Recommendations for further investigation
Crescentic reefs appear to be integral to the understanding of crown-of-thorns starfish outbreaks. There is insufficient knowledge about the hydrodynamics related to this reef type, particularly in summer months when the major flow of water may be from north to south. Research into the flow of water over and around crescentic reefs is recommended. The residence time of water due to the constraining influence of the ribbon-reefs also merits further investigation.
Although extensive work over the last twenty years has provided information on the Halimeda banks, the part they play in total nutrient cycling over the continental shelf is not fully known. Incorporation of the banks into the nutrient budgets of the shelf needs to be undertaken.
Oceanic influx is known to affect the distribution of Halimeda banks. It is also related to ENSO events. Further investigations are required as to the scale of oceanic influence on the outer edge of the shelf and the extent to which it extends across the shelf.
Terrigenous influence on this sector of the Great Barrier Reef is clearly indicated and has been illustrated by numerous, though isolated studies. A study needs to be undertaken to determine the zone affected by mainland runoff and whether or not this has changed in historical times. A suggested strategy would be to carry out a systematic shallow coral core program which could establish the pattern and extent of terrigenous influence through the application of numerous techniques e.g. fluorescence, geochemistry etc.
Relationships between ENSO and crown-of-thorns starfish outbreaks have been suggested. Further work is required on shelf hydrodynamics during contrasting El Niño and anti-El Niño (La Niña) phases.
his report surveys the physical oceanography of the Cairns Section of the Great Barrier Reef Marine Park, against a background of the potential influences of the current regime on the crown-of-thorns starfish phenomenon. The various field studies which have been carried out on the shelf, as well as relevant work in the adjacent Coral Sea, are discussed and evaluated. Also treated are a number of theoretical and numerical modelling studies of the current regime.
The ongoing COTS surveys point to a recent but continuing upsurge in the numbers of starfish in the northern portion of the Cairns Section. This raises the question of whether such populations are a likely precursor to further COTS outbreak episodes. The last outbreak stimulated considerable research on the COTS phenomenon, a novel aspect of which was the combined role played by physical oceanographic field studies and numerical modelling.
The models of Dight and co-workers at that time linked larval transport processes with the currents on the continental shelf. This demonstrated the general south-ward trend of starfish activity. Further modelling work by Black and Burrage has revealed the variability in the extent of larval transport, due largely to the influences of the East Australian Current on continental shelf circulation.
Improvements in computational facilities now allow these early models to be upgraded in a number of ways, through increased spatial resolution, improved model physics and particle release strategies, and the assimilation of real data into the process of model forcing. Such advances need to be accompanied by the acquisition of improved data sets, so that the models can be more comprehensively verified against physical reality. However, the disappearance of large COTS numbers throughout the Great Barrier Reef has been mirrored by a reduction in research support, which now needs to be redressed. The only available long-term current observations come from the Transport of the East Australian Current System (TEACS) current mooring array. This has provided invaluable information about oceanic influences on the continental shelf edge and slope, near the northern and southern extremities of the Cairns Section. Apart from several current measuring programs discussed in the report, which were set up independently of TEACS, no correspondingly long-term data on currents have been collected from the inner and middle shelf. Such data are crucial for a proper quantitative evaluation, calibration, and further refinement of the various numerical models. This would enhance their use in COTS larval transport modelling and in related studies, and thereby develop their potential use for management decision making in the Great Barrier Reef Marine Park.
A key feature influencing low frequency ('mean') currents in the Great Barrier Reef Region is the position at the shelf edge of the bifurcation point for the inflowing South Equatorial Current, where it separates into the East Australian Current and the northward flowing Hiri Current. This generally tends to be located in the northern part of the Cairns Section, but its position also exhibits considerable variability. The relationship between the bifurcation and other physical factors (e.g. winds, oceanic current regime, and other influences such as ENSO), quite apart from the possible effects on shelf currents and larval transport processes, is essentially unknown. The situation in the Cairns Section contrasts with that in both the neighbouring Sections, Central and Far Northern, where much more relevant research has been effected. An improved understanding of the region's circulation will require a more concerted effort than has been made to date, not only in data collection and analysis, but also in various types of numerical modelling.
xisting biological, oceanographic, water quality and environmental data for the Cairns-Cooktown region (14°30'S to 16°55'S) have been reviewed with regard to the contribution of regional features, processes and dynamics to the preferential development of primary crown-of-thorns starfish outbreaks in this region.
In terms of its regional and time-averaged water quality characteristics, the Cairns-Cooktown region does not differ greatly from the Great Barrier Reef shelf as a whole. Taking due regard for systematic differences between data sets, an examination of extant water quality and nutrient data sets shows no clear evidence for widespread eutrophication in the region from natural or anthropogenic sources. Time and spatially-averaged, depth-weighted chlorophyll concentrations are on the order of 0.4 to 0.5 µg L-1 , close to the larval development/starvation threshold suggested by Lucas (1982). Under low-rainfall, low-runoff conditions, chlorophyll concentrations in lagoon waters may only be half this value. A significant proportion (40-80 per cent) of this phytoplankton biomass is in the form of picoplankton (> 2 µm size fraction) which are not optimal food for Acanthaster larvae. Higher persistent chlorophyll concentrations (as an indicator of phytoplankton standing crop) are found elsewhere in the southern Great Barrier Reef (Pompey Reefs 20°S). Resident phytoplankton populations have real primary production rates similar to the Great Barrier Reef as a whole and are characterised by relatively high in-situ growth rates. While blooms of Trichodesmium are regularly observed in the region, Trichodesmium is unlikely to be a significant food source for Acanthaster larvae.
Significant, shelf-scale, but episodic upwelling occurs in the Cairns region and can contribute significantly to shelf nutrient stocks. No large-scale upwelling events have been observed in the Cooktown region to date. Shelfbreak upwelling in the Cooktown region is constrained by the local reef topography and direct effects are most likely limited to the outer shelf.
There is circumstantial evidence supportive of the terrestrial runoff hypothesis for the generation of past primary crown-of-thorns starfish outbreaks in the region. Both the mid-1980s and current (incipient) outbreak were preceded 3-4 years by significant inputs of freshwater to the Cairns-Cooktown shelf from river runoff and rainfall. This freshwater input is presumed to contain substantial dissolved and particulate nutrients. The largest river floods in the region since the late 1950s occurred in 1979 after several 'wet' years (1974, 1977). The major floods of 1981 also appear to have affected the region. Low salinity waters were observed in the Cairns-Cooktown region and it is likely they persisted for several weeks during the likely time for Acanthaster larval development. Widespread distribution of low salinity water and elevated nutrient and chlorophyll levels, which also were likely to have persisted for more than one month, were noted during a prolonged (December-March) monsoonal rain depression which followed cyclone Joy in 1991. Post-cyclone Joy chlorophyll concentrations (ca. 0.5 µg L-1) were above the threshold for successful larval development.
The importance of terrestrial nutrient inputs is likely to be strongly influenced by the retention time of water, nutrients and plankton within the semi-enclosed section of shelf between the Howick Islands (14°30'S) and Cape Tribulation (16°05'S). It is likely that the dense structure of shelfbreak and cross-shelf reefs in the Cooktown region inhibit lateral exchange of shelf waters. However, there is no data or other information regarding water residence times in this region. A program of hydrodynamic modelling is needed to examine flushing in this region and its relation to other environmental forcing factors (e.g. wind stress, tides, floods).
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| FINE-SCALE SURVEYS 1995-96 - Summary Report and Current Status |
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* Note that outbreaking densities on reef numbers 10-12 were restricted to a single habitat only. Hence they were classified as active spot outbreaks (ASO). # Includes reef numbers 10-12. |
The observed trends indicate that by summer 1996-97 many mid-shelf reefs in the survey area will have between 10 to 15 times the number of mature COTS that could really be sustained by the coral community. It appears that the situation is still getting worse with significant local losses in coral cover to be expected over the next few years. Ongoing surveys will continue to monitor the situation and attempt to detect possible new outbreaks at the earliest possible time.
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| COTSWATCH - REEF-USER SURVEY SCHEME |
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| COTSWATCHERS (FEBRUARY-MAY 1996) |
| R Aiello / Great Adventures, Cairns; M Allen / Cairns; D Blackshaw / Great Adventures, Cairns; R Braley / 'Aquasearch'; C Briggs / Great Adventures, Cairns; A Brown / Cairns; F Chapman / QDEH Cardwell; Coral Princess Cruises / Townsville; G Elliott / Borneo Sea Adventures, Malaysia; I Fleetwood / Gladstone; T Geddes / Port Douglas; S Goodhew / Cairns; K Hoppe / Kiel, Germany; P Heatherwick / Port Douglas; C Honchin / Townsville; W Legg / Rockhampton; H Malcolm / QDEH Pallarenda; R Mau / Lismore; S Martin / QDEH Cairns; P Mc Ginnity / Townsvile; S Mordes / Cairns; J Moxham / Port Douglas; J Purcell / Great Adventures, Cairns; C Purdon / QDEH Townsville; S Richards / Cairns; O Schapendonk / Great Adventures, Cairns; R Schutte / Great Adventures, Cairns; S Simpson / Port Douglas; E Suzuki / Vatulele Island Resort, Fiji; K Thomas / Cairns; J Wells / Great Adventures, Cairns; C Williams / Queensland Department of Environment Cairns; M Short / Queensland Department of Environment Cairns; M Wilson / Airlie Beach; D Wiseman / Brinsmead. |
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