Freshwater unionid bivalves are difficult to monitor due to their cryptic, burrowing behavior and their residence in soft substrates. DNA barcode reference sequences are essential for molecular identification and conservation studies of endangered freshwater unionids. For endangered species, the collection of live individuals is often restricted, which limits the construction of such reference databases. In this study, we evaluated the feasibility of using shell-derived DNA from Cristaria plicata as a source for mitochondrial DNA barcoding. Naturally deposited shells were collected from a freshwater environment, and DNA was extracted from five distinct shell regions under different preservation conditions. Mitochondrial 16S rDNA was targeted using both short (180 bp) and long (450 bp) barcode primers. PCR products were sequenced and compared with GenBank reference sequences, and phylogenetic analyses were conducted to confirm taxonomic identity. DNA yield differed substantially among shell regions and preservation states. Phylogenetic analyses demonstrated that sequences derived from shells clustered with established C. plicata references from South Korea and other East Asian populations. However, degraded shell materials occasionally produced divergent or nonspecific sequences, particularly when longer barcode regions were amplified. These results indicate that shell-derived DNA can serve as a viable, noninvasive source for generating DNA barcode references of endangered unionid bivalves. This approach may facilitate the expansion of reference databases and support molecular monitoring and conservation efforts without requiring the collection of live specimens.

This study assessed the benthic macroinvertebrate community structure and aquatic environmental conditions in the eastern Hallyeohaesang National Park. From April to August 2024, three surveys at eight sites in Tongyeong-Hansan and Geoje- Haegeumgang identified 90 species from 4 phyla, with an average density of 4,743 individuals per square meter (ind.m-2). Trichoptera (23 species) and Ephemeroptera (17 species) were the most diverse orders, while non-insect taxa constituted approximately 30% of the total individuals. Functional analysis revealed clingers (CL) and collecting gatherers (CG) as the dominant habitat and feeding groups, respectively. Community analysis indicated that Site 1 had an unstable structure, characterized by a high Dominance Index (DI) and low Diversity Index (H’), Evenness Index (E), and Richness Index (RI). Conversely, Site 4 exhibited the most stable community. Biological water quality assessments, using the Total Ecological Score of Benthic Macroinvertebrate Community (TESB) and Average Ecological Score of Benthic Macroinvertebrate Community (AESB), largely showed Grade A to B quality across most sites. However, Site 1 received a Grade C for TESB, attributed to artificial bottom substrates. Cluster analysis, employing the Bray-Curtis similarity index based on species composition and abundance, grouped the survey sites into three distinct clusters, reflecting variations in surrounding land use and habitat structure. TESB correlated positively with species diversity, richness, and evenness. AESB showed a positive correlation with dissolved oxygen (DO) and negative correlations with water temperature (WT), pH, and electrical conductivity (EC). These results underscore the high sensitivity of these low-flow aquatic ecosystems to environmental factors, emphasizing the critical need for continuous monitoring to ensure their conservation against climate change and non-point source pollution.

This study quantitatively analyzed the ecological niche breadth (ENB) of 27 freshwater mollusk species (11,406 occurrence records) in Korea based on macroenvironmental gradients, including climate, topography, and land cover. We combined Levins’ index values (B: niche breadth, BA: equitability) with optimum-tolerance analysis (optimum value and tolerance range, t95-t05) to determine species-specific habitat strategies and environmental responses. The analysis revealed a distinct dichotomy in the habitat strategies of Korean freshwater mollusks, separating cold-water, lowdisturbance types in upstream areas from warm-water, disturbance-tolerant types in downstream areas, mainly structured by thermal and land-cover gradients. Species, such as Semisulcospira libertina, Radix auricularia, and the alien species Physa acuta, were identified as generalists, showing high B values but low BA values, suggesting that they are capable of inhabiting diverse environments but concentrate their presence in certain environmental conditions. Conversely, Koreoleptoxis nodifila and Clithon retropictum were classified as specialists with low B values and intermediate to high BA values, indicating stable and equitable distribution within restricted environmental limits. Urbanization appeared to be an influential limiting factor, showing low BA values for most species, whereas agricultural areas showed higher BA values, suggesting a comparatively broader habitat possibility. Notably, K. nodifila, a critically endangered and endemic species, showed optimal habitat conditions of low temperature (10.65°C), low urbanization (4.82%), and high forest cover (57.34%), confirming its status as a cold-water indicator species adapted to forested upstream systems. The study findings provide a quantitative framework to assess the environmental tolerance, vulnerability, and conservation priorities of Korean freshwater mollusks.

Freshwater ecosystems support biodiversity and provide essential ecosystem services. In Korea, the Water Environment Information System monitors these ecosystems using separate biological and physicochemical indicators. Complex interactions occur among diverse biological taxa and physicochemical conditions. Thus, integrating heterogeneous monitoring data is crucial for accurately assessing ecosystem health. However, differences in data characteristics between the indicators present significant integration challenges. Given the scale and heterogeneity of the monitoring data, advanced analytical techniques are necessary to detect interactions among variables. This study aimed to identify key correlations among biological and physicochemical indicators by clustering similar variables and removing noise using the Hierarchical Density-Based Spatial Clustering of Applications with Noise (HDBSCAN) algorithm, followed by Spearman’s rank correlation coefficient and maximal information coefficient (MIC) analyses. HDBSCAN effectively eliminated noise indicators and grouped biological and physicochemical indicators into clusters based on shared characteristics, thereby enhancing the interpretability of the correlation analysis. Spearman analysis showed strong associations among biological indicators, particularly among species with similar ecological traits. MIC analysis further detected nonlinear associations between ecological assessment indices and specific biological species, which also reflected similar ecological characteristics. These findings are significant in that the comprehensive analysis of existing monitoring data revealed relationships within biological and physicochemical indicators while preserving the original purpose and function of each monitoring network. This study is expected to serve as a foundational resource for freshwater environmental monitoring and the development of effective management strategies.

From 2017 to 2024, we surveyed 43 diverse aquatic habitats in South Korea, leading to the identification of 18 cyanobacterial taxa that are newly recorded for the country, found across eight sites (about 18% of the surveyed locations). These taxa exhibit a wide range of morphological forms, including unicellular, colonial, filamentous, and heterocytous types, and belong to various orders such as Chroococcales, Synechococcales, Nostocales, and Stigonematales. Notably, this study provides a provisional record of Gomphosphaeria aponina in Korea, correcting its previous misidentification as G. natans. We also documented Dolichospermum compactum, a species that has been genetically reclassified. Additionally, we identified species with the potential to cause harmful algal blooms (HABs), such as Microcystis botrys and Gloeotrichia aurantiaca, which are crucial for domestic water quality monitoring. Currently, only 414 cyanobacterial taxa are recorded in Korea, representing less than 8% of the estimated global total of approximately 5,300 species. This significant gap underscores the considerable unrecorded diversity within Korean aquatic ecosystems. These findings substantially enhance the national cyanobacterial checklist and underscore the need for ongoing monitoring in understudied aquatic environments. They also highlight the importance of integrating classical morphological and ecological observations with advanced molecular methods. This polyphasic approach can accurately detect cryptic diversity and support robust ecological assessments. Overall, this comprehensive floristic expansion offers valuable baseline data for biodiversity inventories, ecological monitoring, and the development of microbial resources within Korean aquatic environments.

This study investigated the effects of elevated salinity on the growth, morphology, and biochemical composition of two freshwater microalgae species: Chlorella thermophila (a green alga) and Anabaena variabilis (a cyanobacterium). The goal was to understand their adaptive mechanisms under saline stress and evaluate their potential for biofuel production. These species were chosen for their ecological significance and contrasting cellular structures (unicellular versus filamentous), which provide complementary insights into salinity tolerance among freshwater microalgae. Cultures were maintained in both standard BG11 medium and artificial seawater medium (SWM) under controlled light intensity (200 μmol photons m-2 s-1) and pH (7.5). Over a cultivation period of 10-20 days, we quantified key parameters, including cell size, volume, chlorophyll a, protein, lipid content, and fatty acid profiles, using microscopy (ImageJ), spectrophotometry, FTIR, and GC-MS analysis. Both species showed increased cell volume and lipid accumulation in SWM, with C. thermophila experiencing a dramatic volume increase from 5.83 μm3 to 54.76 μm3) and a 6.8% rise in lipid productivity. Fatty acid profiling identified distinct fatty acids, such as palmitoleic and pantetheic acids, in C. thermophila cultivated in SWM. These specific fatty acids may indicate adaptive strategies for osmoregulation or metabolic shifts toward energy storage under salinity-induced stress. These findings highlight the potential of salinity-driven modulation of microalgal metabolism to enhance biofuel precursors, offering a sustainable approach for biomass production in saline environments with reduced reliance on freshwater.

The genus Pleurastrum is a coccoid green alga comprising 10 species worldwide. Pleurastrum exhibits simple morphology and high polymorphism, which complicates the understanding of its diversity. We examined the morphological and ultrastructural characteristics of Pleurastrum using light, confocal, and transmission electron microscopy. Additionally, we performed phylogenetic analysis based on multigene sequences (nuclear SSU rDNA, 5.8S, internal transcribed spacer (ITS2) region, and plastid rbcL and tufA genes) from Pleurastrum strains to report two previously unrecorded freshwater species (Pleurastrum insigne and Pleurastrum microstigmatum) in Korea. The vegetative cells were predominantly spherical, with a few being ellipsoidal, and each cell contained a chloroplast with one pyrenoid. The sporangia produced several daughter cells, while the biflagellate zoospores were ellipsoidal and motile. Phylogenetic analysis confirmed that P. insigne and P. microstigmatum form well-supported monophyletic clades. Analysis of ITS2 secondary structures revealed similar patterns, with several differences in nucleotide sequences and insertions between the two species. The findings of this study expand the known distribution of Pleurastrum and enhance our understanding of its species diversity in Korea.

Freshwater bivalves contribute to key ecological functions in lake ecosystems, yet their cryptic and benthic lifestyles often hinder detection through conventional surveys. In this study, we applied environmental DNA (eDNA) metabarcoding to assess the diversity and distribution of unionid bivalves in six lakes across Republic of Korea. Water samples were collected from three sampling strategies-Center Surface, Center Mix, and Waterside Surface-and processed using 16S rDNA-targeted primers followed by high-throughput sequencing. A total of four unionid species (Cristaria plicata, Sinanodonta lauta, Unio (Nodularia) douglasiae, and Anodonta woodiana) were detected across 18 sampling points. Notably, eDNA successfully identified unionid presence in all lakes, even where conventional surveys failed to observe individuals. Among the sampling strategies, Center Mix exhibited the highest values for Shannon and Simpson indices as well as ASV richness. Waterside Surface samples generally showed lower diversity and detection frequency. A Venn diagram of ASV occurrences revealed three ASVs shared across all sampling strategies and one unique ASV found only in Center Mix. These results indicate that sampling location significantly affects detection sensitivity and diversity representation in eDNA-based bivalve monitoring. Combined application of Center Mix and Center Surface strategies may enhance both detection efficiency and species diversity coverage in lentic environments.