Plankton dynamics in a tropical floodplain lake: fish, nutrients, and the relative importance of bottom-up and top-down control
Plankton dynamics in a tropical floodplain lake: fish, nutrients, and the relative importance of bottom-up and top-down control
复制标题
DOI：
10.1111/j.1365-2427.2004.01306.x
复制
发表时间：
2005-01-01
影响因子：
2.7
通讯作者：
De Meester, L
中科院分区：
文献类型：
--
作者：
Rejas, D;Declerck, S;De Meester, L
1. 在拉古纳布费奥斯（Laguna Bufeos）进行了两次圈闭实验，这是一个位于伊奇洛河（玻利维亚）洪泛平原的新热带瓦尔泽湖。实验旨在(1)评估自下而上和自上而下控制对浮游生物群落的相对重要性，(2)评估浮游鱼类对浮游动物的直接和间接影响的相对影响，以及(3)试图确定这些影响的机制。在第一个实验中，自下而上的控制似乎主导了浮游食物网。与无鱼围护区相比，有鱼围护区各浮游动物类群的氧浓度、叶绿素a水平和种群密度均有所增加。优势分类单元Moina minuta的出生率在有鱼的情况下明显高于没有鱼的情况，而死亡率在不同处理之间没有差异。这些结果首次表明，鱼类通过影响营养循环和提高初级生产对甲壳类浮游动物的积极影响可以弥补因鱼类相关死亡而造成的损失。在第二个实验中，不同营养水平的控制方向不同：浮游植物似乎是自下而上的控制，而浮游动物主要是自上而下的控制。添加鱼和营养物质均能提高叶绿素a浓度。由于鱼类的存在，大多数浮游动物种类都减少了。大多数枝海动物的出生率在不同处理之间没有差异，而有鱼围场的死亡率高于无鱼围场。在有鱼存在的情况下，波斯米opsis deitersi达到了更高的密度，可能是因为它们从chaoborus的捕食中释放出来。我们令人信服地显示了与基于营养级联的预期的强烈偏差，支持营养级联可能在热带湖泊中较弱的观点。
1. Two enclosure experiments were carried out in Laguna Bufeos, a neotropical varzea lake located in the floodplain of River Ichilo (Bolivia). The experiments aimed (i) to assess the relative importance of bottom-up and top-down control on the plankton community, (ii) to assess the relative impact of direct and indirect effects of planktivorous fish on the zooplankton, and (iii) to attempt to identify the mechanisms responsible for these effects.2. During the first experiment, bottom-up control seemed to dominate the planktonic food web. Compared with fishless enclosures, oxygen concentrations, chlorophyll a levels and the population densities of all cladoceran zooplankton taxa increased in enclosures with fish. Birth rates of Moina minuta, the dominant taxon, were substantially higher in the presence than in the absence of fish, whereas death rates did not differ between treatments. These results are the first to suggest that the positive effects of fish on crustacean zooplankton via effects on nutrient cycling and the enhancement of primary production can compensate for losses because of fish-related mortality.3. During the second experiment, the direction of control appeared to vary between trophic levels: the phytoplankton appeared to be bottom-up controlled whereas the zooplankton was mainly top-down controlled. Chlorophyll a concentrations were enhanced by both fish and nutrient additions. The majority of the zooplankton taxa were reduced by the presence of fish. Birth rates of most cladoceran taxa did not differ between treatments, whereas death rates were higher in the enclosures with fish than in the fishless enclosures. Bosminopsis deitersi reached higher densities in the presence of fish, probably because of a release from predation by Chaoborus.4. We convincingly showed strong deviations from trophic cascade-based expectations, supporting the idea that trophic cascades may be weak in tropical lakes.