Distribution and dynamics of the marine toxic dinoflagellates Karenia mikimotoi and K. papilionacea in Korean coastal waters using the quantitative real-time PCR method

Abstract

Karenia species are marine unarmoured dinoflagellates and some species contain neurotoxic brevetoxins. They have been reported to appear in offshore or coastal areas influenced by oceanic waters. Over the past decades, blooms of Karenia species have developed in many parts of the world, also causing mass animal mortalities, neurotoxic shellfish poisoning and even respiratory problems in humans (Chang 1999; Tester et al. 2000; Yang et al. 2000; Kempton et al. 2002; Botes et al. 2003; de Salas et al. 2004; Naar et al. 2007; Hoagland et al. 2009). Diagnostic characters to identify Karenia species include the extent of the apical groove and the degree of sulcal extension on the ventral epitheca. However, Karenia species are small in size and their cell shapes are easily deformed after fixation, thereby making it difficult to identify species using light microscopy. Karenia papilionacea is reported to produce neurotoxin, namely brevetoxin-2. However, this species showed high similarity with other Karenia species and thereby often misidentified. Recently, K. papilionacea was first recorded to appear in Korean coastal water. In this study, I used real-time polymerase chain reactions to detect and quantify the abundance of K. papilionacea in Korean coastal waters. I designed a set of species-specific primers to amplify the internal transcribed spacer (ITS) region of Karenia papilionacea and developed a real-time quantitative PCR (qPCR) method to investigate the temporal and spatial distribution of Karenia mikimotoi and K. papilionacea in Korean coastal waters. A linear relationship between the Ct and the log of cell number was always demonstrated (R2>0.98) for all standard curves. The efficiency of the reaction (E) calculated by the formula : E=10(1/m)-1 (where m is the slope of the standard curve : -3.295) high. Field samples were collected from a total of 18 sites in Korean coastal waters during the summer of 2017. K. papilionacea was detected in the samples from 8 sites in the South Sea of Korea. By contrast, K. mikimotoi was detected only from 4 sites, but it showed wider distribution than of K. papilionacea. While both K. mikimotoi and K. papilionacea were absent in eight sites, the two species appeared simultaneously in the two sites of Bangjukpo and Magumpo. The two species appeared simultaneously in Bangjukpo and Magumpo. The abundance of K. papilionacea (2553 cells L-1) was higher than that of K. mikimotoi (31 cells L-1) in the Bangjukpo, K. mikimotoi (894 cells L-1) was higher than K. papilionacea (15 cells L-1) in the Magumpo. During the weekly monitoring at the Yongho Bay in Busan from September to December 2017, and June 2018 to April 2019, K. mikimotoi showed relatively low abundance with the highest abundance of 921 cells L-1 on 26 July. By contrast, K. papilionacea showed high abundance with the highest abundance of 9289 cells L-1 on 26 July. This study revealed that the toxic K. papilionacea appeared in all seasons and showed higher abundance than that of K. mikimotoi in Korean coastal waters during the study period. The bloom dynamics and toxicity of K. papilionacea should be determined in further study.