Detection of Cochlodinium polykrikoides and Gymnodinium impudicum (Dinophyceae) in sediment samples from Korea using real-time PCR

Recurring blooms of fish killing dinoflagellate Cochlodinium polykrikoides has resulted in large economic losses in fisheries industry in Korea. This species has been monitored in water column samples, but its spatial distribution in sediments is poorly understood. To address this area, geographic distribution of C. polykrikoides and morphologically similar species Gymnodinium impudicum in surface sediments of Korea was investigated using species-specific real-time PCR probes targeting the internal transcribed spacer 2 rRNA gene. PCR-inhibitory substances in sediment samples were removed by dilution of DNA extracts from the field samples for preventing false-negative detection. G. impudicum was widely distributed in sediments from East, South, and Yellow Seas. C. polykrikoides was prevalent in sediments from South Sea whereas it was not detected in sediments from East and Yellow Seas. These results indicate that these dinoflagellates may persist in surface sediment likely in the form of cyst and their “seed beds” may exist in sediments of South Sea where blooms of C. polykrikoides occur annually.