The feeding ecology of the intertidal limpet, Siphonaria diemenensis at Griffith Point, Victoria.

This study was conducted from December 1979 to December 1981 to determine the diet of Siphonaria diemenensis in the high and low intertidal zone on the rocky shore at Griffith Point, San Remo, Victoria.

Gut contents analysis indicated that in both zones the limpets were feeding primarily on encrusting brown algae (e.g. Ralfsia verrucosa and Scytosiphon lomentaria). In an experimental manipulation, limpets were excluded from 15 x 15cm areas of rock to determine the change in algae cover in the presence and absence of limpets. Two runs of this experiment were conducted in Zone 1 from February to September and from September to December in 1980. The change in algae cover during the experiment was generally greater in the exclusion plots. This supports conclusions from the gut contents analysis, that encrusting brown algae form the major part of the diet of S.diemenensis.

A growth experiment was conducted from 5 September to 15 November 1981 in Zone 1. There were 12 enclosures (15 x 15cm) with 15 limpets in each. Three enclosures were assigned to each of the 4 treatments; Ralfsia, Scytosiphon, scraped or bare. At the end of the experiment, 5 individuals were collected from each enclosure and their shell lengths and dry tissue weights measured. The mean shell length and dry tissue weights were greater in the Ralfsia and Scytosiphon treatments compared to the bare and scraped indicating that the presence of brown algae can be beneficial to this species of limpet.

Algal abundances were monitored throughout this study by analysing photographs of permanently marked quadrats (50 x 50cm) at each of the study sites (3 sites in Zone 1 and 2 sites in Zone 2). Photographs were taken at monthly intervals from December 1979 to December 1981. In Zone 1, there was a clear seasonal trend in algae cover with a minimum cover in summer (January to March) and a maximum in spring (August to December). In Zone 2, there was no seasonal trend but a 100% cover of encrusting brown algae at all times.

Individual adults were marked in both zones in April 1980 (42 in Zone 1 and 43 in Zone 2) and again in January 1981 (104 in Zone 1 and 66 in Zone 2) by cementing a small numbered label to the shell with a clear epoxy resin. The positions of marked individuals were measured regularly over a period of 8 weeks in 1980 and 1981. Over 70% of individuals were observed to home back to their original positions after 8 weeks with the remainder moving to new positions. Limpets were observed to begin to move at least 1 hour before being exposed to air on a receding tide, and to cease movement between 1 and 2 hours after they were uncovered.

本研究于1979年12月至1981年12月开展，旨在探明维多利亚州圣雷莫格里菲斯点岩岸高低潮间带的迪门管笠贝（Siphonaria diemenensis）食性。

肠道内容物分析表明，两个潮间带的帽贝均主要以结皮褐藻（encrusting brown algae，如疣状网地藻（Ralfsia verrucosa）和绳藻（Scytosiphon lomentaria））为食。本研究设置了人工移除实验，将帽贝排除在15×15cm的岩面区域外，以探究帽贝存在与否对藻类盖度变化的影响。该实验于1980年分两阶段开展：2月至9月为第一阶段，9月至12月为第二阶段，均在1区进行。实验期间，排除样地内的藻类盖度变化幅度整体更大，这一结果佐证了肠道内容物分析得出的结论：结皮褐藻构成了迪门管笠贝（S.diemenensis）食性的主要组成部分。

1981年9月5日至11月15日，在1区开展了生长实验。实验共设置12个15×15cm的围隔，每个围隔内放置15只帽贝。4种处理组（分别为疣状网地藻组、绳藻组、刮除组和裸岩组）各分配3个围隔。实验结束时，从每个围隔中采集5只个体，测量其壳长与组织干重。结果显示，疣状网地藻组与绳藻组的平均壳长及组织干重均显著高于裸岩组与刮除组，表明褐藻的存在对该种帽贝的生长具有积极作用。

本研究全程通过分析研究区域内永久标记样方（50×50cm，1区设3个采样点，2区设2个采样点）的照片来监测藻类丰度。照片拍摄周期为每月一次，时间跨度为1979年12月至1981年12月。1区的藻类盖度呈现显著的季节变化趋势：夏季（1-3月）盖度最低，春季（8-12月）盖度最高。2区则无明显季节变化趋势，其岩面始终保持100%的结皮褐藻覆盖。

研究人员分别于1980年4月（1区42只、2区43只）与1981年1月（1区104只、2区66只），通过透明环氧树脂将带编号的小型标签黏贴在成体帽贝的壳上，对两个潮间带区域的成体帽贝进行标记。1980年与1981年，研究人员连续8周定期记录标记个体的位置。观测结果显示，8周后超过70%的个体返回了初始栖息位置，其余个体则迁移至新的区域。此外，帽贝会在退潮暴露于空气中至少1小时前开始移动，并在暴露后1-2小时内停止活动。