Environmental DNA (eDNA) analysis has emerged as a powerful tool for biodiversity monitoring due to its efficiency, standardization potential, and cost-effectiveness. We evaluated the applicability of eDNAbased zooplankton monitoring in Korean lakes by comparing three DNA methods-eDNA, iDNA, and eiDNA-with traditional microscopy. Sampling was conducted in six lakes with varying conditions. eDNA was obtained from lake water, iDNA from unpreserved zooplankton incubated in water, and eiDNA from zooplankton incubated in ethanol. DNA metabarcoding detected more taxa than microscopy, but dominant taxa overlapped, mainly Daphnia. While DNA methods showed higher richness, Simpson and Shannon indices were higher in microscopy, reflecting differences in quantification methods. These discrepancies reflect methodological differences in how taxa are quantified and suggest that DNA-based approaches may overrepresent certain groups in richness estimates. In addition, false negatives were observed for several common rotifer species (e.g., Keratella, Polyarthra), likely due to incomplete reference databases and high intraspecific genetic diversity. Conversely, some taxa detected only by DNA-particularly small-bodied or rare crustaceans-may represent false positives relative to microscopy. These findings emphasize the importance of improving reference libraries and interpreting DNA results with caution, while also supporting the utility of DNA-based methods as complementary tools in zooplankton monitoring and national biodiversity assessments.

This study analyzed and presented zooplankton species occurrence, diversity distribution, and community composition in ninety lakes across South Korea using samples collected through the “Survey of Lake Aquatic Ecosystem Status and Health Assessment.” When comparing our results with the National Species Checklist, we identified factors within each of the three taxa that warrant improvement due to their influence on diversity assessments. To bridge the gap between the ongoing lake ecosystem surveys and the continually updated National Species Checklist-and to enhance the accuracy of diversity evaluations-we conclude that (1) greater taxonomic rigor must be reflected in the national checklist, and (2) the limitations of morphology-based identification (α-taxonomy) must be addressed. Because the National Species Checklist does not distinguish among species, subspecies, and morphospecies, it can give rise to taxonomic oversplitting and taxonomic inflation, leading to ambiguous diversity-index results. Moreover, the low resolution of morphological identification for zooplankton (at the genus, family, or class level) can introduce errors when comparing communities across habitats or detecting non-native introductions. Although alternatives such as environmental DNA and functional diversity exist, they require further refinement before being adopted in policy; therefore, they should be implemented alongside and in comparison with current aquatic ecosystem health assessment methods.

Recently, Korean government has incorporated the assessment and restoration of river continuity as a key component of its integrated water management policy. While, methodologies for evaluating discontinuities and degradation, as well as the procedures for assessment and restoration, have been developed and proposed, there is a need for further improvement. Therefore, further research is required to establish a conceptual framework for continuity specific to domestic river ecosystems and to formulate appropriate assessment methods and restoration strategies. In this study we conduct a comparative analysis of the concepts, restoration approaches, and comprehensive evaluation methods for river continuity as proposed by Japan, the United States, and the European Union (EU), all of which have long-standing frameworks for river continuity assessment and restoration projects. Each country demonstrates distinct objectives and guidelines: Japan emphasizes habitat continuity within the context of river and watershed continuity, the United States integrates continuity as a tool for watershed management, and the EU prioritizes biodiversity conservation by advocating for the removal of artificial barriers and promoting the restoration of free-flowing rivers (FFR). By investigating these international examples, this study provides insights that can guide the development of long-term strategies and evaluation criteria for securing aquatic ecosystem continuity in Korea.

Zooplankton biomass is essential for understanding the quantitative structure of lake food webs and for the functional assessment of biotic interactions. In this study, we aimed to propose a biomass (dry weight) estimation method using the body length of cyclopoid copepods. These copepods play an important role as omnivores in lake zooplankton communities and contribute significantly to biomass. We validated several previously proposed estimation equations against direct measurements and compared the suitability of prosomal length versus total length of copepods to suggest a more appropriate estimation equation. After comparing the regression analysis results of various candidate equations with the actual values measured on a microbalance-using the coefficient of variation, mean absolute error, and coefficient of determination-it was determined that the Total Length-DW exponential regression equation [W=0.7775×e2.0183L; W (μg), L (mm)] could be used to calculate biomass with higher accuracy. However, considering practical issues such as the morphological similarity between species and genera of copepods and the limitations of classifying copepodid stages, we derived a general regression equation for the pooled copepod community rather than a species-specific regression equation.

In ecosystems within limited resources, interspecific competition is inevitable, often leading to the competitive exclusion of inferior species. This study aims to provide foundational information for the conservation and restoration management of Microphysogobio rapidus by evaluating species’ ecological response to biological factors within its habitat. To understand this relationship, we collected food web organisms from site where M. rapidus coexist with Microphysogobio yaluensis, a specie ecologically similar to M. rapidus, and evaluated the trophic levels (TL), isotopic niche space (INS), and the overlap of INS among fishes within the habitat using stable isotope analysis. Our analysis revealed that the M. rapidus exhibited a higher TL than M. yaluensis, with TL of 2.6 and 2.4, respectively. M. yaluensis exhibited a broad INS, significantly influencing the feeding characteristics of most fish. Conversely, M. rapidus showed a narrow INS and asymmetric feeding relationships with other species, in habitats with high competition levels. This feeding characteristics of M. rapidus indicate that the increase in competitors sharing the similar resources lead to a decrease in available resources and, consequently, is expected to result in a decrease in their density.

Recently, Korean government has introduced Multi Metric Indices (MMI) using various biocommunity information for aquatic ecosystem monitoring and ecosystem health assessment at the national level. MMI is a key tool in national ecosystem health assessment programs. The MMI consists of indices that respond to different target environmental factors, including environmental disturbance (e.g. nutrients, hydrological and hydraulic situation of site etc.). We used zooplankton community information collected from Korean lakes to estimate the availability of candidate zooplankton MMI indices that can be used to assess lake ecosystem health. First, we modified the candidate indices proposed by the U.S. EPA to suit Korean conditions. The modified indices were subjected to individual index suitability analysis, correlation analysis with environmental variables, and redundancy analysis among indices, and 19 indices were finally selected. Taxonomic diversity was suggested to be an important indicator for all three taxonomic groups (cladoceran, copepod, rotifer), on the other hand, the indices using biomass for large cladocerans and copepods, while the indices using abundance were suggested for small cladocerans and rotifers.