Impacts of two introduced suspension feeders in Port Phillip Bay, Australia

This study examined the impacts of 2 of the most common epibenthic suspension feeders, Sabella spallanzanii and Styela clava, in Port Phillip Bay, by transplanting individuals from the surrounding habitat into 2 x 2m experimental plots. Densities in the plots represented naturally occurring densities, ranging from 0.5 to 10 individuals per m-2 for Sabella and from 0.5 to 5 individuals per m-2 for Styela. At the completion of the 10 week experimental period the numbers of alive and dead Sabella and Styela in each plot were counted. The infauna in each plot was sampled by inserting 2 metal cylinders to a depth of 15cm into each plot. The sediment within each cylinder was vacuumed to a depth of 10cm into a 1mm mesh bag using a diver-operated, water-driven suction device. The total area in each plot that was sampled was 0.2m2 (cylinder diameter = 35.5cm). Macrofauna were counted and identified in the laboratory to the lowest possible taxon, which was mostly Family. There were significant effects on individual taxa at Sabella and Styela densities greater than 1-2 individuals per m-2, which are densities greater than those typically recorded in Port Phillip Bay. There was a significant negative relationship between Sabella density and the abundance of lumbrinerid polychaetes and gammarid amphipods, and between Styela density and the abundance of lumbrinerids, tanaids, crustaceans as a group, and the bivalve Laternula rostrata.

本研究以菲利普港（Port Phillip Bay）中两种最为常见的表栖悬浮食性生物（epibenthic suspension feeders）——斯氏帚虫（Sabella spallanzanii）与柄海鞘（Styela clava）为研究对象，将其从周边栖息环境移植至2×2m的实验样地中，探究二者的生态影响。实验样地内的生物密度参照自然种群密度设置：斯氏帚虫的密度范围为0.5~10 个·m⁻²，柄海鞘的密度范围为0.5~5 个·m⁻²。在为期10周的实验周期结束后，统计每个样地内存活与死亡的斯氏帚虫和柄海鞘个体数量。通过在每个样地内插入2个深度达15cm的金属圆筒采集底内动物（infauna）样本：借助潜水员操控的水力抽吸装置，将每个圆筒内的沉积物抽吸至1mm孔径的网袋中，抽吸深度为10cm。每个样地的总采样面积为0.2 m²（圆筒直径为35.5cm）。在实验室中对大型底栖动物（macrofauna）进行计数与分类鉴定，尽可能鉴定至最低分类阶元，多数类群可鉴定至科水平。当斯氏帚虫和柄海鞘的密度高于1~2 个·m⁻²时，会对多个分类类群产生显著影响——该密度高于菲利普港内常规记录的种群密度。研究结果显示，斯氏帚虫密度与吻沙蚕科多毛类（lumbrinerid polychaetes）及钩虾亚目端足类（gammarid amphipods）的丰度呈显著负相关；柄海鞘密度则与吻沙蚕科类群、涟虫类（tanaids）、整体甲壳动物类群以及双壳类喙状鸭嘴蛤（Laternula rostrata）的丰度呈显著负相关。