Developing national-level policies related to climate change induced expansions of invasive species requires predictive modelling at a regional scale level. This study aimed to predict future changes in the habitat distributions of two major invasive alien fish species, Micropterus salmoides and Lepomis macrochirus, in South Korea. An ensemble system with multiple species distribution models was used for the prediction, and gridded water portion data from the linear-structure information on river channels inputted as habitat characteristics of freshwater ecosystem into the models. Bioclimatic variables at 20-year intervals from 2001 to 2100 were generated from predicted temperature and precipitation data under the representative concentration pathway 4.5 and 8.5 scenarios. The overall distribution probabilities of the potential habitats increased with time in both climate change scenarios, and the potential habitats were predicted to expand to upstream areas. Combined with regional ecological value information, such as biodiversity in freshwater ecosystems, these results can be an important basis for deriving regional priority information for managing alien species in climate change. Additionally, the modelling approach is highly applicable to various national-level policies for ecosystem conservation since it is not greatly restricted by spatial scales.

The Chinese striped-necked turtle Mauremys sinensis, introduced into South Korea presumably in 2012, is considered an invasive alien species owing to its devastating impact, including hybridization with the native protected species Reeves’ turtle M. reevesii. Recently, the presence of M. sinensis has been confirmed throughout the country, and several sympatric areas with M. reevesii have been reported. Thus, field surveys were conducted at 47 sites across M. sinensis and M. reevesii habitats in South Korea to determine the extent of hybridization. Five sympatric sites were confirmed, and hybrid individuals were identified at four sites. Genetic analyses (COI and R35) of two individuals from Jeju Island confirmed maternal M. reevesii and paternal M. sinensis lineages. Hybridization presumably does not occur under natural conditions, and the hybrids likely originated from captive breeding. This study identifies for the first time the habitats of M. sinensis and its hybrids in the wild of South Korea. The management measures proposed in the current study could be of value for the conservation of the native species; however, our study did not include reproductive monitoring, and there is a need for such surveys as well as for systematic management of non-native turtles introduced into South Korea.

Salmo trutta, commonly known as brown trout, is an invasive species that has established itself in various regions, including South Korea, where it poses ecological risks to native freshwater fish populations. To enable natural habitat restoration, S. trutta needs to be monitored, but traditional monitoring techniques are associated with several limitations. Therefore, in this study, we aimed to apply a sensitive and specific real-time PCR (qPCR) assay using a set of primers and a hydrolysis probe specific to the mitochondrial cytochrome b gene of S. trutta. Environmental DNA (eDNA) was extracted from river-water samples collected downstream of the Soyang Reservoir and around the Uiam Reservoir between January and March 2023. The qPCR assays successfully detected S. trutta eDNA in 11 of the 24 samples, with high concentrations found upstream and downstream of the Soyang River. Our results demonstrate the effectiveness of qPCR assay for the S. trutta detection in aquatic environments and highlight its potential for monitoring the spread of this species, especially in areas that are difficult to survey using traditional methods. This molecular approach offers a more efficient tool for S. trutta population management, mitigating its impact on native biodiversity.

The largemouth bass (Micropterus salmoides), a food resource in Korea, is a highly voracious predator, designated as an invasive species. It is both diurnal and nocturnal, with high adaptability and reproducibility. Since the predation characteristics are associated with sensitive dynamic visual acuity, we examined the ocular structure of the largemouth bass to investigate the association between photoreceptor cells and feeding behavior. Furthermore, the comparison of the prey-tracking ability of M. salmoides with that of other predatory fish (Coreoperca herzi and Lepomis macrochirus) with similar ecological characteristics revealed the structure and arrangement of photoreceptor cells, typical of a predatory fish in M. salmoides. The double and single cone cells in the retina were present in the regular mosaic patterns of the quadrilateral units, with four double cone cells surrounding a single cone cell. The photoreceptor cells, i.e., the rod, single, and double cone cells of M. salmoides, were smaller (2.3 ± 0.2, 3.82 ± 0.2, and 7.5 ± 0.2 μm, respectively) than those of other species (3.1 ± 0.24, 6.6 ± 0.5, and 11.3 ± 0.4 μm in diameter, respectively, in C. herzi). A smaller diameter of cone cells allows for a high-density arrangement of visual cells, possibly affecting the dynamic visual acuity for prey tracking.

The Korean Demilitarized Zone (DMZ) was established in 1953 during the cessation of the Korean War, which divided the Korean Peninsula into North and South Korea. The DMZ is a representative biodiversity resource because it limits human activities. The current status of faunal diversity in adjacent areas of the DMZ was investigated in five regions at 91 sites from 2015 to 2019. A total of 19,562 individuals were collected and identified, including 81 species, 19 families, and 11 orders. Zacco koreanus was the most abundant fish species (relative abundance of 21.9%), while other key species were Zacco platypus (18.2%), Rhynchocypris oxycephalus (5.2%), Rhynchocypris steindachneri (4.9%), and Pungtungia herzi (3.7%). Notably, twenty-nige endemic and seven Red Data Book species were recorded, and three exotic species, Carassius cuvieri, Micropterus salmoides, and Lepomis macrochirus were found at five sites. Human activities and disturbances were found at 34.0% of all sampling sites, and the highest disturbance factors were river dredging and agricultural use (seven sites), sewage (five sites), and fisheries and development (two sites). We recommend that the governments of South and North Korea collaboratively manage the DMZ to protect ecological diversity and maintain its status as a symbol of peace.