Research Department for Limnology, University of Innsbruck, Mondseestr. 9, 5310, Mondsee, Austria.
Department of Biology, Shenzhen MSU-BIT University, 1 International University Park Road, Shenzhen, Guangdong Province, P.R. China.
Sci Rep. 2022 Jun 22;12(1):10501. doi: 10.1038/s41598-022-14301-y.
Planktonic ciliates are major components of pelagic food webs in both marine and freshwaters. Their population dynamics are controlled 'bottom-up' by prey availability and 'top-down' by microcrustacean predators. In oceans, copepods are the main ciliate predators while in lakes cladocerans are the typical predators. The efficacy by which these functionally different predators control ciliate population dynamics is debated. We, therefore, investigated experimentally the grazing of three microcrustacean predators with different feeding modes on five freshwater ciliates. We then performed a meta-analysis to assess if our findings can be generalised for aquatic ecosystems. We hypothesized that top-down control is stronger in lakes than in the ocean. We find that: (i) average ingestion rates of marine and freshwater microcrustaceans do not differ; (ii) clearance rates of freshwater cladocerans decrease with ciliate size but increase with ciliate size in freshwater copepods; (iii) clearance rates of the marine microcrustaceans is unrelated to ciliate cell size. These findings have implications for the functioning of freshwater and marine food webs: (i) the ciliate-microcrustacean link is stronger in lakes than in the ocean, and (ii) globally top-down control of ciliates is unlikely in the ocean.
浮游纤毛虫是海洋和淡水浮游生物食物网的主要组成部分。它们的种群动态受到猎物供应的“底层控制”和小型甲壳类动物捕食者的“顶层控制”。在海洋中，桡足类是纤毛虫的主要捕食者，而在湖泊中，枝角类是典型的捕食者。这些功能不同的捕食者对纤毛虫种群动态的控制效果存在争议。因此，我们通过实验研究了五种淡水纤毛虫的三种具有不同摄食方式的微型甲壳类动物捕食者的摄食情况。然后，我们进行了荟萃分析，以评估我们的发现是否可以推广到水生生态系统。我们假设顶层控制在湖泊中比在海洋中更强。我们发现：（i）海洋和淡水微型甲壳类动物的平均摄食率没有差异；（ii）淡水枝角类的清除率随纤毛虫大小而降低，但在淡水桡足类中则随纤毛虫大小而增加；（iii）海洋微型甲壳类动物的清除率与纤毛虫细胞大小无关。这些发现对淡水和海洋食物网的功能有影响：（i）纤毛虫-微型甲壳类动物的联系在湖泊中比在海洋中更强，（ii）全球范围内海洋中纤毛虫的顶层控制不太可能。
