Algal Diet of Small-Bodied Crustacean Zooplankton in a Cyanobacteria-Dominated Eutrophic Lake
Algal Diet of Small-Bodied Crustacean Zooplankton in a Cyanobacteria-Dominated Eutrophic Lake
复制标题
以蓝藻为主的富营养化湖泊中小型甲壳类浮游动物的藻类饮食
作者：
I. Tõnno;H. Agasild;T. Kõiv;R. Freiberg;P. Nõges;T. Nõges
在富营养化水域中，小体枝海动物和环状桡足动物越来越多地占大型甲壳类浮游动物的主导地位，在那里它们经常与蓝藻繁殖共存。然而，人们对它们的藻类饮食偏好知之甚少。通过对爱沙尼亚Võrtsjärv高富营养化浅湖浮游植物标记色素的液相色谱分析，研究了小甲壳类动物（cycloplops leuckarti、Thermocyclops oithonoides、Cyclops kolensis和支大洋类Daphnia cucullata、Chydorus sphaericus、Bosmina spp.）季节性周期的放牧选择性。在寒冷的季节，桡足类动物（主要是C. kolensis）偏好食用隐藻（以肠道内容物中的标记色素异黄质为特征），而在5 - 9月，桡足类动物偏好食用小型非丝状硅藻和绿藻（分别以异黄质和叶黄素为特征）。所有研究的枝海洋物种对群落蓝藻（通过角黄素鉴定）具有最高的选择性。对于通常出现在富营养化湖泊中上层的小球藻来说，群落蓝藻可能是它们的主要食物来源，支持它们与蓝藻华共存。丝状蓝藻和硅藻所特有的色素（分别为玉米黄质和岩藻黄质），在Võrtsjärv中占主导地位的藻类，也存在于食草动物的饮食中，但通常被主导浮游动物组合的甲壳类动物所避免。综上所述，这些结果表明，在一个高度富营养化的湖泊中，共生的小体cyclopoi和枝大洋物种具有明显不同的藻类饮食，枝大洋代表了蓝藻碳向食物网转移的主要营养环节。
Small-bodied cladocerans and cyclopoid copepods are becoming increasingly dominant over large crustacean zooplankton in eutrophic waters where they often coexist with cyanobacterial blooms. However, relatively little is known about their algal diet preferences. We studied grazing selectivity of small crustaceans (the cyclopoid copepods Mesocyclops leuckarti, Thermocyclops oithonoides, Cyclops kolensis, and the cladocerans Daphnia cucullata, Chydorus sphaericus, Bosmina spp.) by liquid chromatographic analyses of phytoplankton marker pigments in the shallow, highly eutrophic Lake Võrtsjärv (Estonia) during a seasonal cycle. Copepods (mainly C. kolensis) preferably consumed cryptophytes (identified by the marker pigment alloxanthin in gut contents) during colder periods, while they preferred small non-filamentous diatoms and green algae (identified mainly by diatoxanthin and lutein, respectively) from May to September. All studied cladoceran species showed highest selectivity towards colonial cyanobacteria (identified by canthaxanthin). For small C. sphaericus, commonly occuring in the pelagic zone of eutrophic lakes, colonial cyanobacteria can be their major food source, supporting their coexistence with cyanobacterial blooms. Pigments characteristic of filamentous cyanobacteria and diatoms (zeaxanthin and fucoxanthin, respectively), algae dominating in Võrtsjärv, were also found in the grazers’ diet but were generally avoided by the crustaceans commonly dominating the zooplankton assemblage. Together these results suggest that the co-occurring small-bodied cyclopoid and cladoceran species have markedly different algal diets and that the cladocera represent the main trophic link transferring cyanobacterial carbon to the food web in a highly eutrophic lake.