The ecology and impacts of the introduced basket clam, Corbula gibba in Port Phillip Bay, Australia

This thesis describes the ecology and impact of the introduced European basket clam, Corbula gibba (Olivi, 1792), in Port Phillip Bay, Victoria. A bay-wide survey conducted in 1998 found C. gibba throughout the bay but it was significantly more abundant in deeper, muddier sites. Life history studies carried out at three sites found that two sites were dominated by a single cohort of large adults while the third site had one cohort of adults and one of juveniles. This juvenile cohort grew at a rate of about 4 mm2 per month but experienced high mortality, with only 0.5% surviving a six month period. Longer term abundance patterns available at St. Leonards, and supplemented by this study, found that, between 1969 and 1999, adult density varied between 0 and 106 individuals per m2 while juveniles were found in varying densities in 5 of 6 years sampled. The effect of anthropogenic disturbance on resident populations and subsequent invasion by C. gibba into disturbed sites was assessed experimentally using scallop dredging. Scallop dredging did not affect resident populations but the impact on subsequent invasion by C. gibba could not be determined as recruitment failed to occur over the study period and adult migration was not observed. The effect of ambient densities of C. gibba on endemic species such as the commercial scallop, Pecten fumatus, was investigated experimentally in the field. These experiments found that C. gibba significantly reduced the size and growth of juvenile P. fumatus to a greater extent than an equivalent number of conspecific scallops. Competition for shared food resources did not appear to be the mechanism underlying this impact, however, as dietary studies found that C. gibba was not a superior competitor. Additional studies found that C. gibba did not affect the recruitment of the native bivalves, Mytilus edulis and Electroma Georgiana, but significantly reduced conspecific recruitment. This effect is likely to have implications for the structure of C.gibba populations in the bay.

本论文阐述了外来引入种欧洲篮蛤（Corbula gibba, Olivi, 1792）在维多利亚州菲利普港湾的生态学特征与生态影响。1998年开展的全港湾调查显示，该物种在港湾全域均有分布，但在更深的泥质生境中其丰度显著更高。在三个采样点开展的生活史研究表明，其中两个采样点的种群仅由单一龄组的大型成体构成，而第三个采样点则同时存在成体龄组与幼体龄组。该幼体龄组的月生长速率约为4平方毫米，但死亡率极高，仅0.5%的个体可存活6个月。圣伦纳德兹站点已有的长期丰度数据结合本研究补充的数据后显示，1969年至1999年间，成体密度介于0至106个/平方米之间；而在6个采样年份中，幼体仅在5个年份中被检出，且其密度存在波动。本研究通过扇贝拖网捕捞实验，评估了人为扰动对本地种群的影响，以及欧洲篮蛤向扰动生境的后续入侵效应。实验结果显示，扇贝拖网捕捞并未对本地种群造成影响，但由于研究期间未发生种群补充招募，且未观察到成体迁移现象，因此无法确定欧洲篮蛤对扰动生境入侵的影响程度。本研究还通过野外实验，探究了欧洲篮蛤的环境密度对特有物种的影响，其中包括商业捕捞物种澳洲栉扇贝（Pecten fumatus）。实验结果表明，相较于同等数量的同种澳洲栉扇贝，欧洲篮蛤对澳洲栉扇贝幼体的个体大小与生长速率的抑制作用更为显著。然而，食物资源竞争并非该抑制效应的潜在作用机制，膳食分析结果显示欧洲篮蛤并非更具竞争优势的物种。补充研究表明，欧洲篮蛤并未对本土双壳类（如紫贻贝（Mytilus edulis）和乔治亚隐壳蛤（Electroma georgiana））的种群补充造成影响，但却显著抑制了同种个体的种群补充。该效应可能会对菲利普港湾内欧洲篮蛤的种群结构产生影响。