Variability and long-term change in the demography of the sponge Rhopaloeides odorabile, across the central Great Barrier Reef

Demographic surveys of the sponge, Rhopaloeides odorabile, were conducted across the continental shelf in the central Great Barrier Reef during January and February 2005 using SCUBA. The inner-shelf reefs surveyed (within 20 km of the coastline) were fringing reefs at Curacoa Island, Pelorus Island and Dunk Island. The mid-shelf reefs chosen (between 40 and 60 km from the coastline) were Davies Reef, Kelso Reef and Small Kelso Reef. The outer-shelf reefs surveyed (beyond 60 km from the coastline) were Pith Reef, Dip Reef and Fork Reef.Five replicate 25 m x10 m belt transects, randomly laid along the depth continuum, parallel to the reef slope, were placed at each of three sites, separated by 100 to 200m, on the exposed south-east face of each reef, at depths between 3 and 15 m. This habitat was chosen as Rhopaloeides odorabile prefers high energy environments. For each Rhopaloeides odorabile specimen recorded on each transect, the greatest dimensions for length, width and height were measured to the nearest half centimetre, using a ruler, to allow calculation of volume measurements (estimated for an overall hemispherical, rectangular or, occasionally, a prism shape). Volume estimates also correlate well with actual biomass. Sponge individuals were grouped into four size classes: 4300 cm³ (very large). The depth of each sponge was also recorded.
This research was undertaken to determine differences in abundance, size and distribution of the sponge, Rhopaloeides odorabile, across the continental shelf in the central Great Barrier Reef and to relate the results to environmental factors known to vary across the shelf, such as light availability, currents, nutrients and sedimentation.Data was also be compared with the demographic data for this species documented in:Wilkinson CR and Evans EA (1989) Sponge distribution across Davies Reef, Great Barrier Reef, relative to location, depth, and water movement. Coral Reefs 8, 1-7. doi:10.1007/BF00304685 andWilkinson CR and Cheshire AC (1989) Patterns in the distribution of sponge populations across the central Great Barrier Reef. Coral Reefs 8, 127-134. doi:10.1007/BF00338268

2005年1-2月，研究人员借助水肺潜水（SCUBA），在大堡礁中部陆架海域开展了针对香味棒海绵（Rhopaloeides odorabile）的种群生态学调查。本次调查覆盖的内陆架礁体（距海岸20km以内）为库拉索岛、佩洛鲁斯岛与邓克岛周边的岸礁；中陆架礁体（距海岸40~60km）选取了戴维斯礁、凯尔索礁与小凯尔索礁；外陆架礁体（距海岸60km以外）则包含皮思礁、迪普礁与福克礁。
在每座礁体的暴露东南坡面，设置3个间距为100~200m的采样点。每个采样点沿深度梯度随机布设5条25m×10m的重复带状样带，样带平行于礁坡，布设水深范围为3~15m。选择该生境的原因在于香味棒海绵偏好高能量水环境。
针对每条样带上记录的每只香味棒海绵个体，研究人员使用卷尺测量其长度、宽度与高度的最大尺寸，精度精确至0.5cm，以便基于半球形、矩形或偶尔的棱柱形模型估算其体积——体积估算值与海绵实际生物量具有良好的相关性。本研究将海绵个体划分为4个尺寸等级，其中体积≥4300 cm³的个体被归为极大型，同时记录每只海绵的栖息水深。
本研究旨在阐明大堡礁中部陆架海域内香味棒海绵的丰度、尺寸与分布差异，并将研究结果与已知的陆架梯度环境因子（包括光照水平、海流、营养盐与沉积作用）建立关联。
本研究获取的数据还将与该物种已发表的种群生态学数据进行对比，相关文献如下：Wilkinson CR与Evans EA（1989）《大堡礁戴维斯礁的海绵分布：与区位、水深及水流的相关性》，《珊瑚礁》8卷，1-7页。DOI:10.1007/BF00304685；Wilkinson CR与Cheshire AC（1989）《大堡礁中部海域海绵种群的分布格局》，《珊瑚礁》8卷，127-134页。DOI:10.1007/BF00338268