Spatiotemporal patterns of cladoceran community responses to water level variation in Haixi Lake, southwest China

Hydrological regulation of lakes has been increasingly practiced around the world, with significant ecological consequences. However, little is known on how lake regulation affects community organization and succession. Crustacean zooplankton play a central role in energy transfer along lake food webs because of their intermediate trophic level. Haixi Lake, a mesotrophic deep-water reservoir in southwest China, was a shallow lake by nature but underwent dam construction and reinforcement in 1957 and 1987–1990, respectively. We applied the sediment records of cladoceran remains in Haixi to uncover the spatial and temporal changes of cladoceran assemblages along a gradient of water depth by combining a spatial survey of 27 surface sediment samples with a temporal survey of a well-dated sediment core covering the last 2 centuries. Lake depth was identified to be a paramount factor in driving the temporal and spatial variation of cladoceran assemblages, which was dominated by planktonic cladocerans such as Bosmina. With increasing water levels, a significant loss of benthic cladocerans and species diversity was noted, as well as a long-term decrease in antennule lengths of bosminids. Specifically, a threshold water depth of ∼8 m was found, possibly linked to lake water thermal stability and littoral habitat coverage. Our results highlight that water level serves as a significant factor in structuring zooplankton species composition and body sizes and should be considered for sustainable water management in regulated inland waters.

全球范围内湖泊水文调控的实践日益增多，由此引发的生态效应亦愈发显著。然而目前学界对湖泊调控如何影响生物群落组织与演替的认知仍较为匮乏。甲壳类浮游动物（Crustacean zooplankton）因处于湖泊食物网的中间营养级，在能量传递过程中发挥核心作用。中国西南的中营养型深水水库海西湖（Haixi Lake）原本为浅湖，分别于1957年及1987—1990年实施了大坝建设与加固工程。本研究结合针对27个表层沉积物样品的空间调查，与对一根可精确定年、覆盖近200年的沉积物岩芯的时间序列分析，依托海西湖沉积物中的枝角类（Cladocera）遗体记录，揭示了枝角类群落沿水深梯度的时空变化规律。研究表明，水深是驱动枝角类群落时空变异的核心因素，该群落以象鼻溞属（Bosmina）等浮游型枝角类为优势类群。随着水位升高，底栖型枝角类的丰度与物种多样性均出现显著下降，同时象鼻溞类的第一触角长度也呈现长期降低趋势。具体而言，研究发现水深约8米存在临界阈值，该阈值或与湖泊水体热稳定性及沿岸生境覆盖度相关。本研究结果表明，水位是调控浮游动物物种组成与个体体型的重要因子，在受调控内陆水体的可持续水资源管理中应予以重视。