State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; University of Chinese Academy of Sciences, Beijing 100049, China.
State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Water Res. 2022 Jun 30;218:118483. doi: 10.1016/j.watres.2022.118483. Epub 2022 Apr 21.
Removal of planktivorous fish is used extensively in northern temperate lakes to reduce phytoplankton abundance via enhanced zooplankton grazing. However, whether this method would work also in large subtropical highland lakes to alleviate cyanobacterial blooms is unknown. We conducted a one-year pilot in situ experiment where we removed a substantial biomass of fish in a fenced-in area, followed by a 3-year whole-lake experiment where the dominant fish species (Japanese smelt) was removed in Lake Erhai in southwest China. The fencing experiments showed that between July and November, when the biomass of the removed stock reached 4 g/m, the zooplankton biomass inside the fence increased significantly compared to a control fence. In the full-lake experiment, we found that sustained removal of Japanese smelt led to an increase in the biomass of cladocerans (Daphnia spp. but especially of Bosmina spp.) and a significant decrease in the biomass of Cyanobacteria and Chlorophyta. Additionally, a marked increase in the ratio of zooplankton to phytoplankton biomass, as well as an increase in the body size of cladocerans, emphasising the importance of enhanced top-down control for mitigating cyanobacterial blooms following extensive fish removal. Our results reveal that removal of small fish (here Japanese smelt) can lead to a reduction of the phytoplankton and cyanobacteria biomass through a trophic cascade in highland deep subtropical lakes. Thus fish removal may be a feasible additional restoration tool to external nutrient loading reduction in such lakes.
在北方温带湖泊中，广泛采用去除食浮游动物鱼类的方法，通过增强浮游动物的摄食来减少浮游植物的丰度。然而，这种方法是否也适用于大型亚热带高原湖泊，以缓解蓝藻水华，目前尚不清楚。我们进行了为期一年的现场试验，在围栏内去除了大量的鱼类生物量，随后进行了为期三年的全湖试验，在中国西南部的洱海去除了优势鱼类物种（日本七鳃鳗）。围栏试验表明，在 7 月至 11 月期间，当去除种群的生物量达到 4g/m 时，围栏内的浮游动物生物量与对照围栏相比显著增加。在全湖试验中，我们发现持续去除日本七鳃鳗导致枝角类（特别是 Daphnia 属和 Bosmina 属）生物量增加，蓝藻和绿藻生物量显著减少。此外，浮游动物与浮游植物生物量的比值明显增加，枝角类的体型也增加，这强调了在广泛去除鱼类后，通过营养级联加强自上而下的控制对缓解蓝藻水华的重要性。我们的结果表明，去除小型鱼类（此处为日本七鳃鳗）可通过在高山深亚热带湖泊中的营养级联减少浮游植物和蓝藻的生物量。因此，鱼类去除可能是这些湖泊除减少外部营养负荷之外的一种可行的额外恢复工具。
