The Korean or hard-shelled mussel, Mytilus unguiculatus, previously known as Mytilus coruscus, is one of the most economically and ecologically important bivalves in South Korea. However, the population size of this species has drastically reduced owing to overharvesting and habitat shrinkage. Because its genetic information is poorly documented, we contributed, in this study, the genetic diversity and structural analyses of 246 adult samples of M. unguiculatus from seven populations along the coastal areas of the mainland and islands of South Korea using a microsatellite multiplex assay. Genetic diversity analyzed from eleven polymorphic microsatellite loci was consistently moderate (0.50–0.57) in all populations. No recent bottleneck was found, indicating that the number of the studied populations did not decrease to an extent that resulted in a reduction of genetic diversity. Additional tests did not reveal any genetic structure across them, possibly resulting from constant gene flow, strong dispersal of planktonic larvae, and genetic admixture between wild populations. These results suggest that M. unguiculatus populations along the coastal areas of South Korea should be managed as a single unit. Our study provides crucial information for future genetic monitoring, conservation management, and population restoration plan in preparation for the rapid decline in bivalve resources.

A liver fluke, Clonorchis sinensis is a representative fish-borne parasite infecting humans, and sensitive detection in fish hosts or aquatic environments is important for monitoring infection sources in endemic areas. Conventional diagnostic methods based on microscopy or conventional PCR often show limited sensitivity, particularly under low-parasite conditions. In this study, we developed a high-sensitive and species-specific molecular marker and established a real-time PCR (qPCR)-based diagnostic method targeting metacercariae isolated from freshwater fish, representing the transmission stage of C. sinensis. Primers and a hydrolysis probe targeting the mitochondrially encoded cytochrome c oxidase 1 (COI) gene were designed, and all primer combinations produced stable amplifications with single melt curves in C. sinensis-positive samples. Among them, one combination was finally selected as the optimal marker due to its high specificity, including validation against mixed trematode samples to confirm species-specific detection. The qPCR assay showed excellent linearity (R² = 0.998), with a detection limit of 10¹ copies per reaction and a quantification limit of 10² copies per reaction. In addition, the assay successfully detected C. sinensis DNA in environmental water samples spiked with metacercariae, demonstrating its applicability to aquatic samples for environmental surveillance purposes. Compared with conventional PCR, the developed qPCR method in this study exhibited markedly improved sensitivity in fish-derived samples. Overall, this qPCR assay provides a robust diagnostic tool for laboratory analysis and has potential utility for environmental DNA-based monitoring of clonorchiasis risk areas within a One Health framework.

Leiocassis longirostris, a large benthic catfish, has been classified as Regionally Extinct (RE) in South Korea since the 1970s. Assessing the success of ongoing restocking efforts in the Geum River is challenging due to limitations in traditional capture-based monitoring methods. We developed a highly sensitive, species-specific quantitative real-time PCR (qPCR) assay targeting the mitochondrial cytochrome b gene (mt-cyb) for this restocked fish. Assay validation confirmed high specificity against a panel of 25 co-occurring fish species, including 8 related siluriforms, and an excellent limit of detection of 10 copies per reaction. We applied this assay to environmental DNA (eDNA) extracted from paired water and sediment samples collected from 13 stations across the Geum River Basin. eDNA was detected at three water and five sediment stations. Notably, detection rates and average concentrations were consistently higher in a sediment sample (peaking at 1609.93 copies L⁻¹), an observation consistent with the species’ benthic ecology. These findings provide the first molecular evidence that restocked L. longirostris may disperse and persist in the mid to lower reaches of the Geum River. This validated eDNA qPCR tool is essential for guiding the integrated monitoring and adaptive management strategies required to support the long-term recovery of this ecologically important species. This study is the first species-specific qPCR of the bagrid catfish in South Korea.

Graesiella emersonii is a green microalga, belonging to the phylum Chlorophyta, with ecological and industrial significance. However, its phylogenetic position and mitogenome structure remain largely unexplored. We analyzed the complete mitogenome of G. emersonii GEGS21. This genome was 35,893 bp in length and contained 43 genes that comprised 13 protein-coding, six ribosomal RNA, and 24 transfer RNA genes. Phylogenetic analysis based on six protein-coding genes placed G. emersonii GEGS21 in a strongly supported clade with Pectinodesmus pectinatus, confirming its affiliation within the order Sphaeropleales. This study will provide valuable insights into the mitogenome architecture of G. emersonii, thereby contributing to further elucidation of green algal phylogeny and organelle genomic evolution.

Paralytic shellfish toxins (PSTs) are produced by several toxic species of the dinoflagellate genera Alexandrium and Gymnodinium, and they pose significant threats to marine ecosystems and public health. Rapid and accurate detection of harmful algal blooms (HABs) is essential for effective management. In this study, we developed a multiplex quantitative real-time PCR (qPCR) assay targeting the 28S ribosomal DNA region to simultaneously detect three PST-producing dinoflagellates, Alexandrium catenella, A. pacificum, and Gymnodinium catenatum, in the East China Sea off southern Korea. Species-specific primers and hydrolysis probes labeled with distinct fluorophores were validated for simultaneous detection. The standard curves showed strong linearity (R² > 0.99) and high amplification efficiencies (95.268–99.325%). No cross-reactivity was observed among the 20 non-target microalgal species. Field application of the assay using environmental DNA (eDNA) samples collected during spring successfully detected A. catenella and A. pacificum, whereas G. catenatum was not detected during the survey period. This multiplex qPCR assay provides a rapid and reliable molecular tool for early detection and spatial monitoring of potentially PST-producing dinoflagellates, supporting sustainable HAB management in East Asian coastal ecosystems.