WAMSI Node 4.3.1b - Trophic interactions in selected south-western Australian estuaries - PhD

This study is aimed at identifying the key primary producers, which support abundant fish species with different feeding modes, in a permanently-open (Swan-Canning) and a seasonally-closed (Wilson Inlet) estuary in south-western Australia. The species studied were the sparid Acanthopagrus butcheri (omnivore), the atherinid Leptatherina wallacei (pelagic feeder) and the gobiid Pseudogobius olorum (benthivore). Three complementary, quantitative approaches were used:1) Stomach content analyses to determine the dietary compositions of the above three species and how they vary with body-size and season;2) Stable isotope ratios of C13/C12 and N15/N14 for fish and their prey; and3) Fatty acid biomarkers in fish and dietary items. Stomach content data demonstrated that size-related changes in diet were evident and that dietary compositions of each species differed among estuaries. Stable isotope ratios of N15/N14 showed that the food web in each estuary contained three trophic levels, while the C13/C12 ratio enabled differentiation of the food chains based on detrital material and plankton. Fatty acid data revealed trophic markers for dinoflagellates in A. butcheri and L. wallacei and for diatoms in P. olorum. These findings suggest that:1) the food resources are partitioned within and among species, 2) the dietary compositions differ between estuaries and 3) different sources of organic material support pelagic and benthic food chains

本研究旨在识别澳大利亚西南部两处河口的关键初级生产者——这两处河口分别为常年开放的天鹅-坎宁河口（Swan-Canning Estuary）和季节性封闭的威尔逊湾（Wilson Inlet），它们支撑着多种具有不同摄食模式的鱼类类群。本次研究选取的物种包括鲷科鱼类黑棘鲷（Acanthopagrus butcheri，杂食性）、银汉鱼科的莱氏细银汉鱼（Leptatherina wallacei，浮游食性）以及鰕虎鱼科的伪鰕虎（Pseudogobius olorum，底栖食性）。本研究采用三种互补的定量研究方法：1）胃含物分析：明确上述三种鱼类的饮食组成，及其随体长和季节的变化规律；2）稳定同位素比值（stable isotope ratios）分析：针对鱼类及其猎物，检测碳13/碳12（C13/C12）与氮15/氮14（N15/N14）的同位素比值；3）脂肪酸生物标志物（fatty acid biomarkers）分析：检测鱼类及食物来源中的脂肪酸特征。胃含物数据显示，鱼类的饮食存在显著的体长相关变化，且各物种的饮食组成在不同河口间存在差异。氮同位素（N15/N14）比值分析表明，两处河口的食物网均包含三个营养级；而碳同位素（C13/C12）比值则可区分基于碎屑物质与浮游生物的食物链。脂肪酸数据显示，黑棘鲷与莱氏细银汉鱼体内检测到甲藻（dinoflagellates）的营养标志物，而伪鰕虎体内则存在硅藻（diatoms）的营养标志物。本研究结果表明：1）食物资源在物种内部及物种间存在生态位分化；2）不同河口的鱼类饮食组成存在显著差异；3）不同的有机物质来源分别支撑了浮游食物链与底栖食物链。