Space as a resource for predatory gastropods on Heron Island Reef, Great Barrier Reef

Data on worm-eating gastropod microhabitat use and abundance within microhabitats were collected along transects located on the Heron Island Reef crest between November 1975 and June 1978. All transects were placed parallel with the reef edge within the study area, which was 10-40 m wide by about 1,500 m long, bounded by a rim of coral and coralline algae to seaward and inshore by a rubble bank. The study area was approximately 50 cm above MLW, but remained covered at low tide due to runoff from the reef lagoon.A series of transects were sampled over a period of 4-8 weeks on three occasions: November 1975 (25 transects); June 1978 (20 transects); and June 1978 (20 transects). Each 10 x 1 m transect was divided into forty 0.25 m² quadrats, with 20 quadrats on each side of a 10 m chain. The first two samples were made during daylight low tides and the June 1978 sample was taken on night low tides. Within each transect an estimate of the substratum composition was made by recording the microhabitat type under every 10th link in the chain (17 cm between points). Gastropod use of these microhabitat types was recorded by noting the microhabitat type occupied by each snail, in addition to its species and shell length to the nearest 0.1 mm. All predatory gastropods found in and near the transects were collected in order to determine the gastropods' diets by faecal sample analysis. These gastropods were subsequently returned to within 30 m of their collection sites.Microhabitat resource use was quantified by calculating niche breadth and overlap estimates for all species with numbers of individuals not less than five. These estimates were calculated separately for the November 1975, June 1977 and June 1978 samples. This study of a gastropod assemblage was designed to determine if microhabitat space was a limiting resource at habitat level for predatory gastropods on coral reefs.

1975年11月至1978年6月间，研究人员在苍鹭岛（Heron Island）礁脊沿线布设样带，收集了食蠕虫腹足类的微生境利用情况及其在微生境中的丰度数据。所有样带均平行于研究区内的礁缘布设，研究区宽10~40米、长约1500米，其向海侧以珊瑚和珊瑚藻礁岸为界，向陆侧则以碎石滩为界。该研究区域位于平均低潮位（Mean Low Water, MLW）以上约50厘米处，但因礁湖径流补给，退潮时仍会被海水覆盖。
研究人员分三次、每次耗时4~8周对样带进行采样：1975年11月（25条样带）、1978年6月（20条样带）以及1978年6月（20条样带）。每条10×1米的样带被划分为40个0.25平方米的样方，10米长的样链两侧各布设20个样方。前两次采样均在日间退潮时段开展，而1978年6月的采样则于夜间退潮时段进行。
在每条样带中，研究人员通过记录样链上每第10个链节对应点位的微生境类型来估算基底组成，相邻记录点间距为17厘米。腹足类对上述微生境类型的利用情况，则通过记录每只蜗牛所占据的微生境类型，同步记录其物种信息及精确至0.1毫米的壳长来获取。
为通过粪便样本分析确定掠食性腹足类的食性，研究人员收集了样带内及样带附近发现的所有该类腹足类，随后将这些个体放归至其采集点周边30米范围内。
对于个体数量不少于5只的所有物种，研究人员通过计算生态位宽度与生态位重叠度估算值，对其微生境资源利用情况进行量化。上述估算值分别针对1975年11月、1977年6月及1978年6月的采样数据单独计算。
本项针对腹足类群落的研究旨在探明，珊瑚礁生境中的掠食性腹足类是否以微生境空间作为生境水平上的限制性资源。