 ell, the third year of sampling of the CRC Reef Research Centre / Great Barrier Reef Marine Park Authority / Department of Environment Cairns fine-scale survey program has now been finalised, with 27 mid-shelf reefs having been surveyed this summer season. Unfortunately, every single sampling trip early this year was to some degree affected by cyclones and very strong winds. Needless to say we missed out on surveying a number of exposed reef fronts. Strangely, I could not convince any members of my dive teams to give it a go. I guess the 30+ knot winds and 2-3 metre waves breaking at the reef fronts could have had something to do with it.
As predicted following last year's fine-scale surveys, both the number of reefs affected and the intensity of local outbreaks in this section have increased. Active reef-wide and/or spot outbreaks of crown-of-thorns starfish (COTS) were found throughout the survey area (see figure 1). Localised COTS densities of between 3 and 40 times sustainable levels (= 30 COTS per hectare) were detected. As expected, the proportion of mature starfish in outbreaking populations has also increased significantly since last year. Seven (25.9%) of the 27 reefs surveyed were classified as Active reef-wide Outbreaks (AO), with a further 13 reefs (48.2%) supporting Active Spot Outbreaks (ASO). Seven reefs (25.9%) were classified as non-outbreaking. Recently observed population trends in this area are summarised in table 1.
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As reported last year, the great majority of outbreaking populations of COTS are made up of several year classes, with at least 2-3 strong cohorts making up the bulk of the populations. Size-frequency distributions recorded throughout the survey area provide a clear description of the widespread nature of these multiple, intensive recruitment events that have led to the current outbreaks. The COTS population observed at Coates Reef (17-011) (see figure 2) illustrates the typical size distribution seen on many reefs in this area. Starfish ranging from 2 to 62 cm in diameter were recorded on this reef. Ageing analysis will no doubt confirm the existence of several year classes in this population. Following the completion of other types of analyses, further updates on the outcomes of the surveys will be presented in future issues of COTS COMMS. So stay tuned for more. This intensive sampling program could not have been completed without the invaluable assistance provided by a dedicated bunch of field assistants who toughed it out during last summer's cyclone-affected surveys. My sincere thanks to: Mickaela Bergenius, Jens Bjelvenmark, Jim Cruise, Noreen and Dave Downs, Doris Engelhardt, Michael Hartcher, David Haynes, Selma Klanten, Marie Puotinen, Martin Russell, Marie-Lise Schlaeppy, Niklaus Taylor, Steve Wilkinson.
A special thanks goes to the staff of the Far Northern Region of the Queensland Department of Environment, and in particular Mike Short, Frazer Muir and their field staff who have now been supporting the fine-scale surveys for three years running. Their efforts have greatly assisted in getting a far more comprehensive understanding of recent developments on reefs in the Cairns Section, a task that would have been significantly more difficult without their commitment and support. Again, many thanks to everyone involved.
As usual, my sincere thanks to all contributors for continuing to support this valuable scheme.
What is particularly interesting about these reports is that they coincide with the latest outbreak event in the central parts of the Great Barrier Reef (see above). The apparent synchrony and geographically widespread nature of these latest outbreaks is intriguing in that they suggest that a truly large-scale phenomenon (?) may be affecting reefs in two of the world's great oceans at roughly the same time. Given that these somewhat disturbing trends now being reported from widely separated reefs worldwide, the time has come to step up our efforts aimed at understanding why the outbreaks are happening over such a large area and what the long-term effects on Indo-Pacific reefs really are. As a first step, I would like to ask divers, dive industry staff, other scientists and anyone with an interest in coral reefs to support the new 'COTSWATCH - International' reef monitoring scheme. Identifying currently unaffected as well as outbreaking areas alike has to be a priority at this stage. Furthermore, if new and developing outbreaks can be detected early, appropriate local response measures may be initiated. The editor of 'Asian Diver', a popular dive magazine published in Singapore and distributed throughout most of the Indo-Pacific region has kindly agreed to publish a short 'promotional' article on the proposed 'COTSWATCH - International' monitoring scheme in the next issue of the magazine. Initially, the scheme will use the original `COTSWATCH' form in circulation here in Queensland. However, depending on the success (or failure!) of the launch, a modified, international version may soon be created.
Benzie, J.A.H. and Wakeford, M. 1997,
The present study provides detailed information for the first time on the genetic structure of populations close to the beginning of an outbreak phase, sampling several populations from the presumed region of outbreak origin. The principal objective of the study was to determine sources of recruits to A. planci populations in an attempt to better define the nature of the origin of outbreak populations in the region of 14-16°S. This was to be achieved through interpretation of the genetic structure of those populations by specifically addressing the following questions: 1) Are recruits to those A. planci populations showing a recent increase in population size different in genetic composition, and hence derived from different sources? 2) Is the genetic composition of the present `outbreaks' the same as those described from the 1980s, implying both present and past outbreaks were derived from the same source area? 3) Are there differences in the genetic constitution of different age classes in the same population suggesting temporal variation in the source of recruits, and is this variation the same order of magnitude as any spatial variation observed? Six populations of the crown-of-thorns starfish, A. planci, showing large increases in population size in 1994-95 were examined using 100-300 individuals collected from each population in Nov. 1995 - Feb. 1996. Nine allozyme loci used previously to determine population structure in the 1980s outbreak populations were analysed. The results showed: 1) no significant genetic differentiation among the recent outbreak populations for any age class (2-6 years old), consistent with the recruits to each population being derived from the same source in each year, 2) the 1996 samples clustered with the eight 1986 outbreak populations in a small part of the genetic space spanned by the 1986 non-outbreak populations, suggesting that the outbreak populations were derived from the same source in both 1986 and 1996 and, 3) no significant variation between age classes in each of the six populations suggesting that no change in the source of recruits to these reefs has occurred over the last 5-6 years. The data showed no significant genetic differences between populations and indicated that all populations have derived their recruits from the same gene pool for the last five years. This does not necessarily mean that all populations arose from larvae from one source reef. In combination with data showing simultaneous increases in population size at several reefs (Engelhardt and Lassig in press) and hydrodynamic models indicating much of the region between 14°S and 16°S is highly connected, the genetic data indicate that A. planci found on several reefs in the region act as one panmictic population. The data are consistent with any one or more of a number of reef populations in this region contributing to the production of a pool of recruits that might build up over time until they contribute significantly to colonisation of reefs downstream and give rise to outbreaks in the central and southern Great Barrier Reef. The considerable similarity in the genetic constitution of the 1986 and 1996 sets of outbreak populations is consistent with both being derived from the same source area. Reference: Engelhardt, U. and Lassig, B.R. in press, Crown-of-thorns starfish (Acanthaster planci) outbreaks in the northern Great Barrier Reef, Proc. 8th Int. Coral Reef Symp., Panama City, Panama.
Fisk, D.A., Vail, L. and Hoggett, A. in press,
Two injection regimes using dry acid (sodium bisulphate) were trialled over a 10-month period and both significantly reduced the densities and mean size of COTS on isolated patch reefs. The frequent injection regime (approximately 2 person hours effort per week) was more effective at reducing COTS numbers than the infrequent regime of 15-20 person hours intensive effort every 4 months. A visit interval of 2-3 days was tested in the latter study period and was found to be most effective at maintaining the relatively lowest numbers of COTS on two of the reefs. However, migration of individuals into the treated reefs was probably occurring at a rate that quickly offset the effect of protective measures. COTS numbers increased at a rate which was related to the interval between injection visits. Both regimes of injection effort reduced the mean size of COTS on a patch reef as well. Initial COTS density was probably the most important factor affecting the efficiency of control measures in the short term. Diver experience was also found to be very important. Efficient search methods should include a diver adopting an oblique observation position and a circular swimming motion around a feeding scar. Overhangs and cavities are favoured resting places for COTS, and these require inspections at a number of different angles to detect the starfish. It is recommended that an intensive eradication effort in the initial phases of a control program should be followed by frequent less intensive effort. This is particularly the case where COTS are already on a site and are deemed to be causing noticeable damage to coral. Feeding observations of populations of COTS on the study reefs indicate that few species or growth forms of corals are immune from some damage due to starfish feeding behaviour, especially when a number of COTS size classes are present. This also is the case when a reef is at an infestation stage and there is high coral cover of Acropora available, which is the preferred food of COTS. Over the eight-month and ten-month study periods, most of the coral community parameters thought to be sensitive to the impact of COTS aggregations showed no significant change when compared to sites where no COTS injections took place. Indices included live and dead coral cover as well as an index of mortality, fragmentation rates, and relative abundance of coral species. Hard coral cover generally decreased over the first eight months but there was no difference between any of the treatments in this trend. The cover of Acropora spp. decreased over the eight months but this decrease was lower in the untreated sites compared to all the treated sites. As the numbers of COTS did not decrease at the non-manipulated sites, the likely explanation for this result is the relatively higher initial cover of Acropora spp. at these sites. A significant increase in the mortality index (ratio of dead to live coral cover) at the unmanipulated sites compared to the treated sites occurred at the same time as a significant decrease over time in the mean index value. This may indicate that the period of the injection regimes was not sufficient to significantly alter the expected changes in community structure under the prevailing circumstances of COTS densities and migration rates. Also, it is most likely that the differences between treatment sites in coral cover (particularly Acropora spp.) was too large for an effect of treatment regimes to be detected over the period of the study. Alternatively, the period prior to the commencement of the study when COTS were present in large numbers may have been too long as they may have changed prior to the start of this study. |
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
