Introduction

Invasive alien species pose a serious threat to biodiversity, ecosystem services, and socioeconomic stability worldwide (Early et al., 2016; IPBES, 2019). Freshwater ecosystems are particularly vulnerable to biological invasions (Kiruba-Sankar et al., 2018), and experience significant disruptions through habitat destruction, competition between invasive and native species, predation, and disease transmission (Britton, 2023). Procambarus clarkii, commonly known as the red swamp crayfish, is a globally recognized invasive species owing to its exceptional environmental adaptability, rapid dispersal capability, and high fecundity (Souty-Grosset et al., 2016). A single female P. clarkii can lay approximately 200-500 eggs in a single spawning event, and this species is known to outcompete native crayfish, predate on aquatic organisms, and act as a vector for crayfish plague (Aphanomyces astaci) (Diéguez-Uribeondo & Söderhäll, 1993; Holdich et al., 2009; Jung et al., 2023). In response to these ecological threats, the species was officially designated as an “ecosystem-disturbing species” in South Korea in 2019 and has since been under strict regulatory control (Korea Law Information Center, 2019).

Media coverage plays a critical role in shaping public perceptions and influencing policy decisions regarding invasive species management. However, misidentifications, the use of incorrect species imagery, and lack of scientific verification in media reports can lead to unwarranted public anxiety and erosion of trust in government interventions (Ballari & Barrios-García, 2022). In particular, when incidents of invasive species are exaggerated or misrepresented in the press, discrepancies may arise between the actual ecological risks and policy responses, undermining effective management strategies.

Reports of P. clarkii in the Byeongcheon Stream were published in both 2023 and 2025, raising public concern regarding the possible reestablishment of this invasive species in the region. The 2023 case involved a single specimen that was later presumed to be an abandoned pet owing to the absence of additional findings (NIE, 2023). In 2025, a similar incident occurred when a local non-governmental organization (NGO) collected a crayfish specimen near the Eunseokgyo Bridge and reported it as P. clarkii to the media without expert validation. This led to widespread media coverage and increased public anxiety. Subsequent investigations, however, confirmed that the specimen was actually Cambaroides similis, a native crayfish species. This study scientifically investigated the incidence of invasive species through field surveys, environmental DNA (eDNA) analysis, and morphological and molecular identification, aiming to reassess the accuracy of the initial report and emphasizing the necessity of expert verification and scientific evidence in invasive species management.

Case Report

On April 28, 2025, a joint field survey was conducted by the National Institute of Ecology (NIE), Geum River Basin Environmental Office, and a local NGO. The survey targeted a section of the Byeongcheon Stream approximately 11.6 km in length, encompassing the area where P. clarkii was previously reported in 2023. Five sites were selected within this segment based on habitat characteristics favorable to P. clarkii, such as slow water flow, abundant aquatic vegetation, and wetland-type features. At each site, three fyke nets were deployed for over 12 hours to capture crayfish specimens (Fig. 1). To address the temporal limitations of conducting a single field survey, this study was complemented with eDNA analysis, which provided an indirect but robust means of verifying the potential presence of P. clarkii, thereby strengthening the overall reliability of the findings (Chucholl et al., 2021; Mauvisseau et al., 2018; Riascos et al., 2018).

Surface water samples (2 L each) were collected from four sites: one upstream, two midstream, and one downstream (Fig. 1). Samples were stored in sterile bottles and transported to the laboratory on ice. Water was filtered through 0.45 µm-glass fiber filters, which were stored in sterile tubes at –20°C until DNA extraction. eDNA was extracted using a DNeasy Blood & Tissue Kit (Qiagen, Hilden, Germany) following the manufacturer’s protocol. P. clarkii-specific cytochrome c oxidase subunit I (COI) fragments were amplified using the Pcl-CO1-0409f and Pcl-CO1-0597r primers (Knudsen et al., 2019; NIE, 2023). The polymerase chain reaction (PCR) conditions consisted of an initial denaturation at 94°C for 10 minutes, followed by 30 cycles of 94°C for 30 seconds, 60°C for 30 seconds, and 72°C for 30 seconds, and a final elongation at 72°C for 10 minutes. The amplification results were confirmed by electrophoresis on a 2.0% agarose gel. Sterile water served as the negative control, and P. clarkii genomic DNA was used as the positive control.

Three additional crayfish specimens collected near the Eunseokgyo Bridge by the NGO were transferred to the NIE for species identification. Morphological features, including branchiostegal suture shape, chela tuberculation, and rostrum morphology, were examined for taxonomic differentiation (Table 1, Fig. 2). For molecular analysis, the COI gene was amplified using the universal primers LCO1490 and HCO2198. The resulting sequences were compared with reference sequences in GenBank to confirm species identity.

Discussion