First Record of the Potentially Toxigenic Diatom Pseudo-nitzschia lundholmiae (Bacillariophyceae) from Jeju Island, South Korea

다국어 초록 (Multilingual Abstract)

The marine diatom genus Pseudo-nitzschia includes several species capable of producing the neurotoxin domoic acid (DA), which causes amnesic shellfish poisoning (ASP) and contributes to harmful algal blooms (HABs) worldwide. However, the diversity and toxicity of Pseudo-nitzschia in Korean coastal waters, particularly around Jeju Island, remain poorly understood. In this study, we investigated the morphology, phylogeny, and toxin production of Pseudo-nitzschia isolated from the coastal waters of Jeju Island, South Korea. A monoclonal strain (PLSG02F8) was established from seawater samples collected in April 2022. Morphological observations using light and scanning electron microscopy, together with ITS1–5.8S–ITS2 rDNA phylogenetic analyses, identified the strain as Pseudo-nitzschia lundholmiae, representing the first confirmed record of this species in South Korean waters. The Jeju strain showed morphological features generally consistent with previous descriptions, with slightly greater cell width and cell overlap. Phylogenetic analysis revealed that the Jeju strain clustered with P. lundholmiae strains from Malaysia and China. Toxin analysis using HPLC confirmed DA production, with a maximum intracellular content of 1.89 fg cell⁻¹ during the early logarithmic growth phase. These results demonstrate that P. lundholmiae is a potentially hazardous DA-producing species in Jeju coastal waters and provide essential baseline data for HAB monitoring and risk assessment.