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You are at - Home | Research | Monitoring ________________________________________________________________________ Survey report Report on surveys of reefs in the Capricorn-Bunker
Dates:
18th
November–
4th
December
2008
Summary Four reefs in the Capricorn-Bunker sector and seven reefs in the Swain sector of the Great Barrier Reef were surveyed using manta tows. Detailed SCUBA surveys for benthic organisms, reef fishes and agents of coral mortality (SCUBA searches) were completed on all reefs. Preliminary results of the manta tow surveys and SCUBA searches are presented in this report. COTS were recorded at Lady Musgrave Island in the Capricorn-Bunker sector during SCUBA searches and at Chinaman Reef in the Swain sector during manta tows. In both cases COTS were in low numbers. No Active Outbreaks have been recorded in the Capricorn-Bunker sector since surveys began in 1985 or in the Swain sector since 2006. However, four of the seven Swain reefs remain listed as Recovering from past outbreaks. Hard coral cover was moderate (10-30%) on all reefs in the Capricorn-Bunker sector and had remained stable on two reefs and decreased on the other two reefs since last surveyed one to two years previous. Major storm damage (as evidenced by overturned corals and rubble banks) had occurred on the exposed reef fronts on all four reefs in the Capricorn-Bunker sector. Hard coral cover in the Swain sector varied from very low (0-5%) to very high (>50%) but in all cases cover had remained stable since surveyed one to two years previous. The Swain reefs where hard coral cover was lowest were those recovering from COTS outbreaks that had persisted for up to 14 years prior to the mid 2000’s. SCUBA searches found relatively high incidences of "white syndrome" (a disease-like necrosis found particularly on tabulate Acropora spp.) on four reefs in the Swain sector. Incidences of "skeletal eroding band" coral disease had also increased on a few reefs in the Swain sector and one reef in the Capricorn-Bunker sector. Incidences of "brown band" coral disease and numbers of Drupella spp. (coral feeding snails) had increased on one reef in the Capricorn-Bunker sector since 2006. A summary of the results is presented in Tables 1 and 2. A full list of survey reefs appears in the Long-term Monitoring Status Report Number 8. Details of the monitoring program design, the sampling methods and a full explanation of the COTS outbreak terminology used in this report can be found on the AIMS reef monitoring website.
Capricorn-Bunker Sector Four reefs were surveyed by both manta tow (Table 1) and SCUBA (Table 2). No COTS were recorded during manta tows and all reefs remain classified NO Outbreak. No active outbreaks have been recorded on these reefs since surveys began in the mid 1980’s. Four adult COTS were recorded during intensive SCUBA searches at Lady Musgrave Reef, but low numbers of COTS have been observed at this reef on a number of occasions since surveys began. Median reef-wide live coral cover on the four reefs was moderate (10-30%) based on manta tow surveys (Table 1). Coral cover had remained stable at One Tree Reef and Wreck Island Reef since last surveyed one to two years previous but had fallen considerably at Broomfield Reef (40-50% to 10-20%) and Lady Musgrave Island Reef (50-60% to 20-30%). These declines in coral cover are largely due to the effects of major storms (at all reefs, areas exposed to prevailing south-east swells were littered with overturned and broken corals). Based on the extent of algal overgrowth, observations from staff at One Tree Island Research Station and the fact that storm damage was not evident at Broomfield Reef when last manta towed in November 2007, we estimate that major storm swells damaged these coral communities sometime between December 2007 and June 2008. A similar event occurred in this sector in the late 1980’s. Such cycles of disturbance and recovery are likely to be the norm on exposed reef faces in this sector as coral communities are dominated by relatively fragile plating and branching Acropora species making them particularly vulnerable to storm damage.
Table 1. Summary of manta tow survey results for the Capricorn-Bunker sector.
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