Abstract

The spatio-temporal distribution of toxic phytoplankton was investigated in seven designated shellfish growing areas along the southern coast of Korea from April 2021 to March 2022. Vegetative cells of eight toxic phytoplankton species were monitored using the Utermöhl method, and additional environmental DNA analysis and resting cyst surveys were conducted at nine sampling stations in Hansan-Geojeman area (Designated Area No. 1). Results revealed that Pseudo-nitzschia spp. occurred most frequently in all areas, while Alexandrium spp., Dinophysis spp., and Prorocentrum cordatum were identified as the predominant toxic phytoplankton. In Hansan-Geojeman area, vegetative cells of Alexandrium spp. increased during February-March 2022, and environmental DNA analysis identified A. catenella and A. pacificum as the dominant species. A significant correlation was observed between the paralytic shellfish toxin-producing gene sxtA and A. catenella in the environmental DNA analysis, while resting cyst surveys demonstrated high occurrence frequencies at specific stations (stations 1 and 9). This study provides fundamental data for monitoring toxic phytoplankton in shellfish growing areas along the southern coast of Korea, validates the appropriateness of the existing monitoring stations, and suggests the necessity of additional monitoring stations.