Daphnia versus copepod impact on summer phytoplankton: functional compensation at both trophic levels
Daphnia versus copepod impact on summer phytoplankton: functional compensation at both trophic levels
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水蚤与桡足类对夏季浮游植物的影响：两个营养级的功能补偿
作者：
U. Sommer;F. Sommer;B. Santer;E. Zöllner;K. Jürgens;C. Jamieson;M. Boersma;K. Gocke
本文报道了一项mesocom研究，比较了微噬和巨噬浮游动物对浮游植物自上而下的影响。我们将来自德国Schöhsee中营养湖的一个物种丰富的夏季浮游植物组合暴露在微噬枝海水蚤hyalina×galeata和巨噬桡足类组合的对数级丰度梯度中。在两个梯度中，浮游植物总生物量、叶绿素a和初级产量对浮游动物密度的响应都很弱，甚至不显著。与体积参数的微弱响应相反，两个浮游动物类群对浮游植物种类组成的影响都很强。桡足类抑制大型浮游植物，而纳米浮游藻类随桡足类密度的增加而增加。水蚤抑制了小型藻类，而大型藻类则以生物量补偿了损失。自养小浮游生物在两个梯度上随浮游动物密度的增加而减少。两种浮游动物官能团都能培养凝胶状的群集藻类，而中等大小（约3000µm3）的非凝胶状藻类则被两种官能团抑制。当水蚤在大约10天后开始入侵并在桡足类中生态系统中生长时，功能混合的浮游动物组合的影响变得明显。与单一官能团的影响相反，两个浮游动物类群的共同影响导致浮游植物总生物量大幅下降。
Here we report on a mesocom study performed to compare the top-down impact of microphagous and macrophagous zooplankton on phytoplankton. We exposed a species-rich, summer phytoplankton assemblage from the mesotrophic Lake Schöhsee (Germany) to logarithmically scaled abundance gradients of the microphagous cladoceran Daphnia hyalina×galeata and of a macrophagous copepod assemblage. Total phytoplankton biomass, chlorophyll a and primary production showed only a weak or even insignificant response to zooplankton density in both gradients. In contrast to the weak responses of bulk parameters, both zooplankton groups exerted a strong and contrasting influence on the phytoplankton species composition. The copepods suppressed large phytoplankton, while nanoplanktonic algae increased with increasing copepod density. Daphnia suppressed small algae, while larger species compensated in terms of biomass for the losses. Autotrophic picoplankton declined with zooplankton density in both gradients. Gelatinous, colonial algae were fostered by both zooplankton functional groups, while medium-sized (ca. 3,000 µm3), non-gelatinous algae were suppressed by both. The impact of a functionally mixed zooplankton assemblage became evident when Daphnia began to invade and grow in copepod mesocosms after ca. 10 days. Contrary to the impact of a single functional group, the combined impact of both zooplankton groups led to a substantial decline in total phytoplankton biomass.