Survival rates of juvenile crown-of-thorns starfish (Acanthaster planci) at Davies Reef, Great Barrier Reef

Predator exclusion experiments, using laboratory reared juvenile crown-of-thorns starfish (Acanthaster planci), were carried out in an area of dead coral rubble on the leeward side of Davies Reef, at depths between 12 and 15 m. One month post settlement starfish were deployed in February 1991, while 4 and 16 month old starfish were deployed in May 1991 and 7 month old starfish were deployed in August 1991. Three different sized plastic boxes with tight fitting lids were prepared for the different age groups of starfish and the lids and sides of the boxes were covered with mesh. After deployment, the mesh on the boxes was cleaned every 1 to 2 days to remove silt and the adequacy of water flow through the mesh was tested periodically.Starfish were placed in boxes with either a natural rubble treatment or a control rubble treatment. The natural rubble treatment consisted of pieces of unconsolidated dead coral rubble, complete with algal and motile epifaunal assemblages, which were collected directly from the seabed at the time of deployment. The control rubble treatment was made up of sun bleached or beach collected coral rubble, which was conditioned in flow-through aquaria for several weeks to allow algal and epifaunal assemblages to develop.Ten boxes of each of the control rubble and natural rubble treatments were used for the 1, 4, and 7 month old starfish, while 5 natural rubble treatments only were used for the 16 month old starfish. In addition, 5 replicate open boxes (natural rubble treatment, without lids) were deployed with 7 month old starfish, allowing free movement of the starfish and predators in and out of the boxes. Open boxes containing 1, 7 and 16 month old starfish were deployed inside larger boxes as escape controls and on recovery the numbers of starfish which had moved to the outer boxes were counted. The number of starfish placed in each box was dependent in the age class of the starfish and the number of starfish available in each age class.The boxes were recovered after 6, 13, 16 and 13 days for the 1, 4, 7 and 16 month old starfish respectively. The contents of each box were washed into bottles and fixed in mixture of buffered 10% formalin in seawater and Rose-Bengal stain. Prior to fixing, any starfish, which could be recovered alive were removed, counted and measured (greatest diameter). The fixed material was sorted by washing the rubble over 6, 1 and 0.1 mm mesh screens and then the rubble was individually washed over the mesh. All starfish were then recovered from the mesh screens and counted and measured. Other epifauna in the 1 mm screen were also counted and categorised with the aid of a dissecting microscope.
This research was undertaken to investigate mortality rates of small crown-of thorns starfish. In these field experiments, the survival of small starfish living in their natural habitat was compared with that of starfish provided with similar food resources and shelter, but in the absence of potential predators or other hazards.

捕食者排除实验采用实验室饲养的幼年长棘海星（Acanthaster planci），在戴维斯礁（Davies Reef）背风侧的死珊瑚碎石区进行，水深介于12至15米之间。1月龄（附着后1个月）的海星于1991年2月投放，4月龄和16月龄的海星于1991年5月投放，7月龄的海星于1991年8月投放。针对不同年龄段的海星，制备了三种不同尺寸且配有紧密盖子的塑料箱，箱盖和箱体侧面均覆盖有网纱。
海星被放置在含有自然碎石处理组或对照碎石处理组的箱子中。自然碎石处理组由未固结的死珊瑚碎石块组成，包含藻类和活动性底栖动物群落，这些碎石块在投放时直接从海床采集。对照碎石处理组由日晒漂白或海滩采集的珊瑚碎石组成，这些碎石在流水水族箱中驯化数周，以促进藻类和底栖动物群落的生长。
对于1月龄、4月龄和7月龄的海星，对照碎石和自然碎石处理组各使用10个箱子；而16月龄的海星仅使用5个自然碎石处理组的箱子。此外，针对7月龄海星设置了5个重复的开放式箱子（自然碎石处理组，无盖），允许海星和捕食者自由进出箱子。装有1月龄、7月龄和16月龄海星的开放式箱子被放置在更大的箱子内作为逃逸对照，回收时统计转移到外部箱子的海星数量。每个箱子中投放的海星数量取决于海星的年龄段以及各年龄段可获得的海星数量。
针对1月龄、4月龄、7月龄和16月龄的海星，分别在投放后6天、13天、16天和13天回收箱子。每个箱子的内容物被冲洗到瓶中，并固定在缓冲的10%福尔马林海水溶液与玫瑰红染色剂的混合液中。固定前，回收所有存活的海星，计数并测量其最大直径。固定后的样本通过在6mm、1mm和0.1mm网筛上冲洗碎石进行分类，然后将碎石分别在网筛上冲洗。随后从网筛中回收所有海星，计数并测量。借助解剖显微镜对1mm网筛中的其他底栖动物进行计数和分类。
本研究旨在调查小型长棘海星的死亡率。在这些野外实验中，比较了生活在自然栖息地的小型海星与在无潜在捕食者或其他危险但食物资源和庇护所相似的环境中的海星的存活率。