ABSTRACT

Sea level rise threatens ecosystem function in coastal lakes by increasing salinity and altering community composition. As mobile generalists, fish have considerable influence on the stability of a system by impacting trophic network structure. Understanding their diet across abiotic gradients, including salinity, can show key characteristics of their ecological role, and predator diet shifts may serve as warning signs of food web restructuring. Stomach contents analysis was used to look at the diet of Retropinna retropinna (common smelt) across shallow coastal lakes on Rēkohu (Chatham Island). Smelt diets from 10 lakes (seven freshwater; three salt-influenced) were analysed. Comparisons of salt-influenced and freshwater lakes showed shifts in composition. Smelt in freshwater lakes predominantly consumed herbivorous, omnivorous, or predatory insect larvae while diet in salt-influenced lakes was dominanted by crustacean shredders. Population diet varied somewhat less among salt-influenced lakes than among freshwater lakes, suggesting homogenisation of smelt diet with salinity. Differences in composition and heterogeneity did not translate to consistent differences in total niche width or individual specialisation between freshwater and salt-influenced lakes. Further development of knowledge on biological structure across salinity gradients is essential to understand ecosystem function under future climate scenarios.

摘要

海平面上升会增加盐度并改变群落组成，从而威胁沿海湖泊的生态系统功能。作为移动的多面手，鱼类通过影响营养网络结构对系统的稳定性产生相当大的影响。了解它们在非生物梯度（包括盐度）中的饮食可以显示其生态作用的关键特征，而捕食者饮食的转变可能是食物网重组的警告信号。胃内容物分析用于观察Retropinna Retropinna的饮食（常见胡瓜鱼）穿越 Rēkohu（查塔姆岛）的沿海浅湖。对 10 个湖泊（七个淡水湖；三个受盐湖影响）的胡瓜鱼饮食进行了分析。受盐湖和淡水湖的比较显示了成分的变化。淡水湖泊中的胡胡瓜鱼主要捕食草食性、杂食性或掠食性昆虫幼虫，而受盐湖影响的胡瓜鱼主要以甲壳类碎肉动物为食。与淡水湖泊相比，受盐影响的湖泊中的人口饮食变化稍小，这表明胡瓜鱼的饮食随盐度的变化而趋于同质化。组成和异质性的差异并没有转化为淡水湖和受盐湖影响的总生态位宽度或个体专业化的一致差异。