Habitat point records from 1983 Smith Isles of Scilly littoral fauna survey

This report covers work done under contract to the NCC which was part only of a larger survey of the Isles of Scilly and is therefore far from comprehensive. The remit was limited to descriptions of selected stations and lists of Mollusca found and these data alone are inadequate for the drawing of conclusions regarding the conservation importance of the area, but should be used in conjunction with the results of other surveys. Seventeen stations were surveyed, all habitats investigated, standard samples of Fucus serratus and small algae taken for laboratory analysis of their associated fauna. Mollusca, Polychaeta, Pycnogonida and other fauna were recorded. Most stations investigated were moderately sheltered. The rock of the Scillies is mostly granite, which weathers into angularly jointed rock with gullies and fissures. There were few habitats suitable for species associated with softer rock and/or crevices. Large areas are boulder beds. When covered with algae these support an extensive fauna, but others are somewhat barren. The sandflats are composed of rather mobile granite sand with a small carbonate fraction and scouring of adjacent rock and boulder areas occurs. A few small patches of Zostera were examined. The discussion notes that about 90 species of Mollusca were found. Reasons for this paucity of Mollusca were suggested as follows: Lack of variety of habitat. Large amounts of coarse, unstable sand with lowered infaunal populations and sand scouring and choking of adjacent rocky areas. Lack of carbonate in the sand and absence of finer sediments. Absence of some species due to isolation - larvae in the plankton from mainland coastal areas not reaching the Isles of Scilly. Currents come chiefly from the Atlantic or south-west Ireland and, as well as water movement, the time spent in the plankton may be a barrier to larvae. Past species lists of Mollusca are noted as being very long; it is suggested that the fall-off in Mollusca populations might be due to the considerable reduction in the amount of Zostera in the 1930's with subsequent increase in mobility of the sand. A comparison of Mollusca found during this survey was made with other island areas. Where there was little variety of habitat, the molluscan fauna was broadly comparable, but where stable sediments were present the numbers of species on the shore were much higher. However, comparison of data from all those areas for Mollusca associated with small algae does not indicate marked differences. It is concluded that the nature and variety of habitat, both on the large and small scale, is the most important, and on present knowledge the most easily understood factor governing the diversity of Mollusca in an area. Rich sites were identified - the richest stations were characterised by boulders upon, but not embedded in stable gravel, with shallow pools and running water in moderate exposure. Of the sediment areas, the most sheltered were the richest. Three areas surveyed during this investigation have been the subject of previous reports, and the findings of these reports were briefly discussed. Records currently considered sensitive have been removed from this dataset.

本报告涵盖了根据NCC合同完成的工作，这仅是针对塞文群岛的更大规模调查的一部分，因此远非全面。研究范围仅限于对选定站点的描述以及所发现的软体动物名录。这些数据本身不足以就该地区的保护重要性得出结论，但应与其他调查结果结合使用。共调查了十七个站点，调查了所有栖息地，并采集了标准样品的锯齿状海藻和小型藻类，以供实验室对其相关生物群进行分析。记录了软体动物、多毛类、星虫类及其他生物群。大多数调查站点具有适度的遮蔽。塞文群岛的岩石主要是花岗岩，风化成具有沟壑和裂缝的角状节理岩。适合与较软岩石及裂缝相关物种的栖息地很少。大面积为砾石层。当覆盖着藻类时，这些区域支持广泛的生物群，但其他区域则相对贫瘠。沙滩由较易移动的花岗岩沙和少量的碳酸盐组成，且相邻的岩石和砾石区域发生了侵蚀。考察了几小块海莴苣。讨论中指出，发现了大约90种软体动物。造成软体动物数量稀少的原因如下：栖息地多样性不足。大量粗粒、不稳定的沙子导致底栖生物种群减少，以及相邻岩石区域的沙子侵蚀和堵塞。沙子中缺乏碳酸盐和细粒沉积物。一些物种因隔离而缺失——来自大陆沿海地区的浮游幼虫无法到达塞文群岛。主要水流来自大西洋或西南爱尔兰，除了水流运动外，幼虫在浮游生物中的时间也可能是障碍。记录显示，过去软体动物的物种列表非常长；有人提出，软体动物种群数量的下降可能归因于20世纪30年代海莴苣数量的显著减少以及随后的沙子流动性增加。本调查中发现的软体动物与其他岛屿地区的比较表明，在栖息地多样性较少的地区，软体动物群落总体相似，但在存在稳定沉积物的地区，岸边的物种数量要高得多。然而，对与小型藻类相关的软体动物的所有这些地区的数据进行比较，并未显示出明显的差异。结论认为，无论是从大尺度还是小尺度来看，栖息地的性质和多样性是决定该地区软体动物多样性的最重要因素，并且根据现有知识，这是最容易理解的因素。识别了丰富的地点——最丰富的站点特点是位于稳定的砾石之上的砾石，而不是嵌入其中，并有浅水池和流动水，位于适中的暴露环境中。在沉积物区域中，最遮蔽的区域最为丰富。调查中的三个区域此前已有报告，并对这些报告的发现进行了简要讨论。目前被认为敏感的记录已从本数据集中移除。