Surveys to locate juvenile crown-of-thorns starfish (Acanthaster planci) on the Great Barrier Reef

In 1989, reefs in the central GBR were surveyed to locate high density populations of larger (5-15 cm) juvenile crown-of-thorns starfish (Acanthaster planci). Preliminary surveys were undertaken at two inshore reefs (Hayman Island and Reef No. 20-019) in October 1989. During November 1989, searches were carried out at different depths at 45 sites on 12 reefs. The reefs surveyed were 19-123, 19-124, 19-131, 19-138, Bait, Bowden, Davies, Hope, Little, Oublier, Rafter and Stanley.All reefs surveyed were relatively small and had supported large numbers of starfish during the 1970s. At the time of survey they either supported large numbers of adult starfish or were located immediately to the south of the main concentration of reefs with outbreaks. A range of reef types across the continental shelf were surveyed. The perimeter of each reef was surveyed by manta tow to identify sites with relatively high live coral cover and small areas of dead coral then 3 or 6 sites were selected for more intensive SCUBA swim searches.SCUBA searches were undertaken by divers along 4 depth contours at each site: reef crest/flat, 5m, 10m and 15m. Where this was impractical, the divers swam parallel to each other and covered the maximum practical depth range between the crest and the base of the reef slope. The four divers swam slowly along their respective depth contours for a set period of twenty minutes, covering a distance of approximately 100m. Whilst swimming, each diver scanned approximately 1m either side of the swim path looking for any small starfish or evidence of their presence. All small areas of recently dead coral were closely examined and if no starfish were found, then an attempt was made to determine the cause of mortality. The following observations were recorded during each 20 minute swim search: number of adult crown-of-thorns starfish, number and size of juvenile (Additional dives were undertaken at night on Stanley and Bait Reefs, in areas where numerous small coral scars had been recorded during the day. These involved 5 divers who searched for juveniles within an area approximately 100x50m, over a 90 minute period. Surveys were undertaken to locate high density populations of juvenile crown-of-thorns starfish (Acanthaster planci), which could be used in further studies of recruitment, predation and population dynamics of the juvenile stage this starfish. Only 14 juvenile starfish were found in the 1989 survey.Observations have been expanded since 1989 and some aspects have been incorporated into the ongoing AIMS Long Term Monitoring Program - refer to the separate metadata record on 'Agents of coral mortality'.

1989年，研究人员对大堡礁（Great Barrier Reef, GBR）中部的珊瑚礁开展调查，以寻找体型较大（5~15厘米）的幼年长棘海星（Acanthaster planci）的高密度种群。1989年10月，研究人员在两座近岸珊瑚礁（海曼岛礁与20-019号礁）完成了预调查。1989年11月，研究人员在12座珊瑚礁的45个采样点开展了不同水深的搜索工作。本次调查的珊瑚礁包括19-123、19-124、19-131、19-138号礁，以及Bait、Bowden、Davies、Hope、Little、Oublier、Rafter与Stanley礁。所有被调查的珊瑚礁体量均相对较小，且在20世纪70年代曾支撑过大量长棘海星种群。本次调查开展时，这些珊瑚礁要么栖息着大量成年长棘海星，要么紧邻暴发虫害的珊瑚礁主集群以南区域。研究人员对大陆架上的多种类型珊瑚礁进行了勘测：采用蝠鲼拖曳法（manta tow）对每座珊瑚礁的周边区域进行排查，以识别活珊瑚盖度较高、死珊瑚分布面积较小的采样点，随后从中选取3~6个点位开展更为精细的水肺潜水（SCUBA）游泳搜索。潜水员在每个采样点沿4条深度等高线开展水肺潜水搜索，分别为珊瑚礁礁冠/礁坪、5米、10米与15米水深区域；若该方案不可行，则潜水员以平行编队游动，覆盖礁冠至礁坡基部之间的最大可行水深范围。4名潜水员沿各自的深度等高线缓慢游动，设定时长为20分钟，游动距离约为100米。游动过程中，每名潜水员会对泳道两侧各约1米的范围进行扫视，以寻找小型长棘海星或其活动痕迹。研究人员会对所有近期出现死珊瑚的小区域进行细致检查；若未发现长棘海星，则会尝试确定珊瑚死亡的诱因。每次20分钟的游泳搜索过程中，需记录以下观测数据：成年长棘海星的数量、幼年长棘海星的数量与体型。此外，研究人员在Stanley礁与Bait礁的日间调查中发现多处小型珊瑚疤痕区域，随后在夜间开展了额外潜水作业：5名潜水员在约100×50米的区域内开展了90分钟的幼年长棘海星搜索工作。本次调查旨在寻找幼年长棘海星的高密度种群，以便后续开展该物种幼体阶段的补充、捕食与种群动态相关研究。1989年的本次调查仅发现了14只幼年长棘海星。自1989年以来，相关观测数据得到了扩充，部分内容已纳入正在进行的澳大利亚海洋科学研究所（Australian Institute of Marine Science, AIMS）长期监测计划——相关细节可查阅题为《珊瑚死亡诱因》的独立元数据记录。