Alexandrium catenella (Group I) and A. pacificum (Group IV) cyst germination, distribution, and toxicity in Jinhae-Masan Bay, Korea.

To better understand the outbreaks of paralytic shellfish poisoning and bloom dynamics caused by Alexandrium species in Jinhae-Masan Bay, Korea, the germination and distributions of ellipsoidal Alexandrium cysts were investigated, and paralytic shellfish toxins (PSTs) profiles and contents were determined using strains established from germling cells. The phylogeny and morphological observations revealed that the germinated vegetative cells from ellipsoidal cysts collected from the surface sediments in Jinhae-Masan Bay belong to Alexandrium catenella (Group I) and A. pacificum (Group IV) nested within A. tamarense species complex. Cyst germinations of A. catenella (Group I) were observed at only 10 °C, whereas cysts of A. pacificum (Group IV) could germinate at temperature ranges of 10 to 25 °C. Maximum germination success (85%) for isolated cysts occurred at 15 °C, and the germling cells were A. pacificum (Group IV). The results indicate that the variation in water temperature in Jinhae-Masan Bay can control the seasonal variations in germination of cysts of A. catenella (Group I) and A. pacificum (Group IV). The germination rates of ellipsoidal Alexandrium cysts were different among sampling sites in Jinhae-Masan Bay, probably because of differences in distribution and abundance of A. catenella (Group I) and A. pacificum (Group IV) in the sediments. The ellipsoidal Alexandrium cyst concentrations were much higher in February than in August, however the distributions were similar. Gonyautoxins 3 and 4 (GTX-3 and GTX-4) contributed a large proportion (>90%) of the toxins produced by strains A. catenella (Group I) and A. pacificum (Group IV) established from germling cells, and the total cellular contents were higher in A. catenella (Group I) than in A. pacificum (Group IV).