Distribution and abundance of juvenile starfish in the central Great Barrier Reef

The densities of juvenile Acanthaster planci (Crown-of thorns starfish) were sampled at 16 inner mid-shelf reefs of the central Great Barrier Reef during trips in July, September and November 1986 and were resurveyed in November/December 1987. The reefs sampled were: Lodestone, Keeper, Little Broadhurst, Bowden, Mid, Stanley (3 independent surveys), Old, Charity, Hope, Showers, Bait, Ross, Square, Robertson, Credlin and Bushy-Redbill.A destructive sampling technique was chosen due to the small size and cryptic behaviour of the starfish during their first 10-12 months of benthic development. On each reef two replicate 10x1m transects were sampled at each of two arbitrarily chosen sites located within three depth zones (reef base, reef crest and reef flat) and two exposure categories (windward and leeward). Surface features of each transect were mapped with a resolution of 15cm. Loose and detachable pieces of substrate were removed, broken into small pieces and searched underwater for the presence of stafish. While the study was primarily focused on Acanthaster planci, all starfish species were recorded. The position of each starfish encountered was recorded on the substratum map and the specimen retained for subsequent identification and measurement. Sampling of a transect ceased either when it reached bed rock or a depth of 30cm.In order to determine the precision of the sampling method, the reef with the highest densities observed on the first cruise in 1986 (Stanley Reef) was resurveyed twice more during subsequent cruises that year.In both 1986 and 1987, transects at one leeward site on each of four reefs were sampled nocturnally. Twelve 12 transects were marked out and 6 were sampled in the usual way during the day and 6 were searched without destruction after 2100 hours. This research was undertaken to:1. define the juvenile habitat of Acanthaster planci and 2. investigate the spatial and temporal abundance of juveniles and their contribution to the population outbreaks observed in this species.

1986年7月、9月及11月的科考航次中，研究人员于大堡礁（Great Barrier Reef）中部的16个内陆陆架中部礁盘上，对长棘海星（Acanthaster planci，Crown-of-thorns starfish）的幼体密度开展采样，并于1987年11—12月进行了复勘。本次采样涉及的礁盘包括：Lodestone、Keeper、Little Broadhurst、Bowden、Mid、Stanley（共开展3次独立采样）、Old、Charity、Hope、Showers、Bait、Ross、Square、Robertson、Credlin以及Bushy-Redbill。

鉴于该海星在底栖发育的前10—12个月体型微小且具有隐蔽行为，研究选用了破坏性采样技术。在每个礁盘内，于3个深度带（礁底、礁脊与礁坪）以及2个暴露类别（向风岸与背风岸）中各随机选定两个采样点，每个采样点布设两条重复的10×1米样带。每条样带的表面特征以15厘米的分辨率进行测绘。随后移除松散易脱落的基底物，将其破碎为小块后在水下搜寻海星个体。尽管本研究主要聚焦长棘海星，但所有海星物种均被记录在册。每一只被发现的海星的位置均被标注在基底地图上，并留存标本用于后续的物种鉴定与尺寸测量。样带采样将在抵达基岩或深度达到30厘米时终止。

为评估采样方法的精度，研究人员于1986年后续的科考航次中，对首次航次中观测到密度最高的礁盘——斯坦利礁（Stanley Reef），额外开展了两次复勘。

1986年与1987年，研究人员在4个礁盘的各一个背风岸采样点开展夜间采样。本次共布设12条样带，其中6条以常规方式在日间采样，剩余6条则在21:00后进行非破坏性搜寻。

本研究旨在达成两项核心目标：1. 明确长棘海星的幼体栖息地；2. 探究幼体的时空分布丰度及其对该物种种群爆发的贡献。