During the past century, many brackish shallow lakes worldwide have become eutrophic. How the zooplankton have responded to this development is not well elucidated. Here, we analysed the decadal changes (from 1999–2000 to 2017–2018) in zooplankton biomass, body mass, and potential top-down control on phytoplankton during summer in 4 Danish shallow brackish lakes (Lund Fjord, Han Vejle, Selbjerg, and Glombak) subjected to varying degrees of eutrophication. Significant reductions of zooplankton biomass, body mass, the ratio of large-sized cladoceran to total cladoceran biomass, and the ratio of zooplankton to phytoplankton biomass were observed in low to moderately vegetated lakes (Selbjerg and Glombak). However, in the macrophyte-dominated lake (Han Vejle), zooplankton biomass, body mass, and the contribution of large-sized cladocerans (Daphnia spp.) to total cladoceran biomass increased without a corresponding increase in the zooplankton to phytoplankton biomass ratio, which may be attributed to the refuge effect of submerged macrophytes. Using the pooled dataset, multivariate analysis indicated that total phosphorus concentrations and fish abundance were the main drivers of shifts in the zooplankton community and that zooplankton body mass was strongly negatively related to fish abundance. From a lake management perspective, our results suggest that eutrophication, through increased fish predation and reduced submerged vegetation abundance, has major effects on zooplankton communities in temperate coastal brackish shallow lakes, and a reduction in the zooplankton grazing pressure on phytoplankton is predicted if the eutrophication process continues.

在过去的一个世纪中，全世界许多咸淡的湖泊都变得富营养化。浮游动物如何对这种发展做出反应尚不清楚。在这里，我们分析了4个丹麦浅咸湖（隆德峡湾，汉·维伊勒，塞尔比约格和拉脱维亚）在夏季期间浮游动物生物量，体重和浮游植物潜在的自顶向下控制的年代际变化（从1999–2000年至2017–2018年）。 Glombak）遭受了不同程度的富营养化。在低度至中度植被覆盖的湖泊（Selbjerg和Glombak）中观察到了浮游动物生物量，体重，大型枝角藻与总枝角藻生物量的比例以及浮游植物与浮游植物生物量的比例显着降低。然而，在以大型植物为主导的湖泊（汉·维埃勒）中，浮游生物的生物量，体重和大型枝角类鱼类的贡献（水蚤对总枝ado生物量的增加没有使浮游植物与浮游植物生物量之比相应增加，这可能归因于被淹没的大型植物的庇护作用。使用汇总的数据集，多变量分析表明，总磷浓度和鱼的丰度是浮游动物群落变化的主要驱动力，并且浮游动物的体重与鱼的丰度强烈负相关。从湖泊管理的角度来看，我们的结果表明，通过增加鱼类的捕食和减少淹没的植被的丰度，富营养化对温带沿海微咸浅湖中的浮游动物群落具有重大影响，如果预测了富营养化，则预计浮游动物的放牧压力会降低过程继续。