Abundance, distribution and trophic potential of cryptofauna at Davies Reef, Great Barrier Reef

The major groups of motile cryptofauna inhabiting dead coral substrata across a transect at Davies Reef were quantified in terms of abundance, biomass and density.Samples of dead corals of similar size were collected by enclosing a piece of protruding dead coral substrate with a plastic bag and detaching a piece with a masonry hammer. Collections were made at 7 locations in November 1985: on the front slope at 10 m depth; on the front crest; on the main flat; where the main flat borders the lagoon at 10 m depth; on the outer back reef on the flat; and on the outer back reef at 10 m depth. Five replicate samples were collected at each of 6 sites (3 inside, 3 outside damselfish territories) where possible, at each location. Stegastes apicalis territories were present in the reef flat and reef crest locations. The front slope location contained Plectroglyphidodon lacrymatus territories. Two locations did not have damselfish territories. Sampling was repeated in August 1986 at 2 locations (reef flat and reef crest), to provide an estimate of seasonal variation in cryptofaunal abundance. Ten replicate samples were collected both within and outside fish territories at each location.Cryptofauna were extracted in the laboratory and any animals too large to be washed through a sieve of 1 cm mesh were excluded from the analysis. Individuals within each of the 5 most common taxonomic groups (amphipods, copepods, other crustaceans, polychaetes and molluscs) were counted. Separate counts of crustaceans were also made to a finer taxonomic level (gammarideans, caprellids, isopods, cumaceans, tanaids, ostracods, decapods). Biomass was measured (ash-free dry weight) for the 5 common taxonomic groups for the November 1985 samples only.Chlorophyll a was used as an index of algal biomass present on the coral rock. Following pigment extraction, the surface areas (SA) of coral blocks were estimated using a latex-coating method. Blocks were photocopied, and their projected surface area (PSA) measured by digitising those images. The ratio of PSA to SA was taken as a measure of surface complexity.The expected food consumption rate of cryptofauna for each sample was calculated using the published allometric relationships between measured ingestion rate, individual body mass and the organic fraction of the food source (epilithic algal community), for a range of small macroinvertebrates representative of the taxa collected in the study. Ingestion rates were converted to cryptofaunal group rates based on the average density of that group for all locations. This research was undertaken to:1. determine if there were variations in density and biomass of major groups of motile cryptofauna across environmental and biotic zones on a coral reef2. determine if there were variations in cryptofauna within and outside damselfish territories3. assess the trophic importance of motile cryptofauna as grazers on coral reefs4. provide preliminary estimates on the grazing rates of reef cryptofauna Cryptofauna refers to small motile invertebrates inhabiting the epilithic algae and crevices on the surface of the coral rock.

本研究对戴维斯礁（Davies Reef）一条样带上栖息于死珊瑚基质中的主要运动型隐生动物群（Cryptofauna）进行了丰度、生物量及密度的定量分析。

研究人员通过塑料袋包裹突出的死珊瑚基质，并使用石工锤敲取的方式，采集了大小相近的死珊瑚样本。1985年11月，研究人员在7个地点开展了样本采集工作，具体包括：深度10米的前坡、前脊、主平坦区、主平坦区与潟湖交界处（10米深）、外礁后平坦区、以及深度10米的外礁后区域。在每个地点，研究人员在6个站点（3个位于雀鲷领地内，3个位于领地外）尽可能采集了5份重复样本。礁平坦区和礁脊区域存在顶斑高身雀鲷（Stegastes apicalis）的领地，前坡区域则有泪突吻鲈（Plectroglyphidodon lacrymatus）的领地，另有两个地点无雀鲷领地分布。

1986年8月，研究人员在两个地点（礁平坦区和礁脊）重复了采样工作，以评估隐生动物群丰度的季节性变化。在每个地点的鱼领地内和领地外，均采集了10份重复样本。

研究人员在实验室中提取隐生动物群，并排除了无法通过1厘米孔径筛网的大型个体。随后，对5个最常见类群（端足类、桡足类、其他甲壳动物、多毛类和软体动物）的个体数量进行了统计；同时，对甲壳动物类群进行了更精细的分类统计（包括钩虾类、麦杆虫类、等足类、涟虫类、异足类、介形类和十足类）。仅针对1985年11月采集的样本，研究人员测量了上述5个常见类群的生物量（无灰干重）。

研究以叶绿素a作为珊瑚岩上藻类生物量的指标。色素提取后，研究人员采用乳胶涂层法估算珊瑚块的表面积（SA）；同时，通过对珊瑚块的影印图像进行数字化处理，测量其投影表面积（PSA）。PSA与SA的比值被用作衡量表面复杂度的指标。

研究人员利用已发表的异速生长关系（涉及实测摄食率、个体体重及食物来源（岩表藻类群落）的有机组分），计算了每个样本中隐生动物群的预期食物消耗率；这些异速生长关系适用于本研究中采集到的代表性小型大型无脊椎动物类群。随后，基于各隐生动物群在所有地点的平均密度，将个体摄食率转换为类群水平的摄食率。

本研究旨在：
1. 探究珊瑚礁不同环境和生物区带中主要运动型隐生动物群的密度及生物量是否存在差异；
2. 分析雀鲷领地内与领地外的隐生动物群是否存在差异；
3. 评估运动型隐生动物群作为珊瑚礁牧食者的营养级重要性；
4. 初步估算珊瑚礁隐生动物群的牧食率。

隐生动物群（Cryptofauna）指栖息于珊瑚岩表面岩表藻类及缝隙中的小型运动型无脊椎动物。