From Large-Bodied Dominance to Small-Bodied Prevalence: Seasonal Shift in Zooplankton Community Structure and Its Environmental Drivers in the Tropical Songtao Reservoir, China

As essential artificial water bodies in the tropics, tropical reservoirs are characterized by high year-round water temperatures and significant seasonal fluctuations in terrestrial inputs driven by rainfall. These unique hydrological rhythms and nutrient dynamics profoundly drive the succession of aquatic biotic communities. Taking the Songtao Reservoir as a case study, this research conducted sampling at 47 sites across the Nanfeng, Fanjia, and Yacha areas during the dry season of 2023 and the rainy season of 2024. The study calculated community alpha-diversity indices and employed Generalized Linear Models (GLM) for analysis. The results indicate that environmental factors exhibit significant seasonal and spatial variations; furthermore, the zooplankton community demonstrates a clear seasonal turnover in body-size structure, where large-bodied groups (such as cladocerans and copepods) dominate during the rainy season, whereas small-bodied groups (including rotifers and nauplii) become dominant during the dry season. Small-bodied groups respond more sensitively to environmental changes and act as key drivers of the shifts in community structure. The study reveals that the zooplankton community in Songtao Reservoir follows a dynamic pattern characterized by "seasonal dominance and spatial modification". These findings uncover the adaptive strategies of zooplankton in tropical reservoirs and provide a scientific basis for reservoir ecological management.