For the sustainable use of lake ecosystem services—water resources, aquatic habitats for biodiversity conservation, and aesthetic values as waterfront space—ecosystem health assessments using biota are implemented as important national environmental monitoring projects. Zooplankton play a key role as an important linkage in the material circulation as secondary producers in lake ecosystems. At the same time, they influence the composition and biomass of other communities through biological interactions. In this review, we summarize useful zooplankton indices for ecosystem health assessment and suggest considerations for their use. Suggestions are provided for the practical application of indirectly measured zooplankton biomass, as well as the potential and limitations of eDNA application, which has recently been actively utilized in biological monitoring.

This study analyzed the relationship between zooplankton communities and water quality characteristics, with a focus on total organic carbon (TOC), in 22 reservoirs within the Geum River basin that share similar climatic conditions but exhibit varying levels of pollution. Across all reservoirs, zooplankton community structures showed the highest correlations with TOC, suspended solids (SS), chlorophyll-a (Chl-a), and Secchi depth (SD), with stronger associations observed for rotifers and cladocerans compared to copepods. The classification of zooplankton community composition patterns, followed by an analysis of their associations with TOC concentrations, revealed relatively distinct differences between high-TOC and low-TOC reservoirs, indicating that TOC functions as a key determinant of community composition. Meanwhile, network analysis based on overall water quality characteristics indicated that patterns of water quality similarity among zooplankton-based communities differed somewhat from those based solely on TOC concentrations, suggesting that TOC may exert an independent influence on zooplankton community structure. In high-TOC reservoirs, typical eutrophic characteristics—such as elevated chlorophyll-a, total phosphorus, and suspended solids, along with reduced water transparency—were observed, accompanied by higher zooplankton abundance and a greater proportion of rotifers within the community. In contrast, low-TOC reservoirs, despite exhibiting no marked differences in other water quality variables, showed higher diversity of cladocerans alongside rotifers, further supporting the independent role of TOC in shaping zooplankton community structures. These findings highlight TOC not only as a general indicator of pollution but also as an ecologically significant factor influencing zooplankton community composition and carbon dynamics in reservoir ecosystems. They suggest that TOC should be considered a key variable in future assessments and management of lentic ecosystems.

Kellicottia bostoniensis is a rotifer species originating from North America, with numerous reports documenting its spread to Europe and South America. Meanwhile, in Asia, the occurrence of this non-native species has been scarcely documented, but its presence was recently reported in Korea in 2020. In Korea, the close geographic proximity of artificial reservoirs within a small area is expected to make the region vulnerable to the spread of K. bostoniensis. Therefore, it is deemed necessary to study the spatio-temporal distribution of K. bostoniensis, which appears to have extensively proliferated across the region, and its relationship with environmental factors. We analyzed the response of K. bostoniensis occurrence to environmental factors and aimed to compare its response patterns with those of potential competitor and predator groups, which were classified based on a functional group approach. This study, conducted on 12 small lakes located under similar climatic conditions, revealed that the response of K. bostoniensis to variables representing the trophic state of the lakes differed from those of the potential competitor and predator groups. The study sites, encompassing a wide range of trophic states from oligotrophic to hypereutrophic, across various lakes and survey periods, were well-suited for examining these relationships. Furthermore, when TSI was calculated to compare the abundance of K. bostoniensis and potential competitors across trophic conditions, the abundance of potential competitors was proportional to TSI. In contrast, K. bostoniensis exhibited higher abundances in mesotrophic and lower eutrophic environments, which distinguished it from its competitors. Our results indicate that the impact of introduced K. bostoniensis on native communities is minimal, while the resistance of native communities through the biological filter based on biological interactions is ineffective against this non-native rotifer species. This provides key evidence for explaining the widespread distribution of K. bostoniensis across continents.