Toxic dinoflagellate Centrodinium punctatum (Cleve) F.J.R. Taylor: An examination on the responses in growth and toxin contents to drastic changes of temperature and salinity.

To understand environmental effects affecting paralytic shellfish toxin production of Centrodinium punctatum, this study examined the growth responses, and toxin contents and profiles of a C. punctatum culture exposed to drastic changes of temperature (5-30 °C) and salinity (15-40). C. punctatum grew over a temperature range of 15-25 °C, with an optimum of 20 °C., and over a salinity range of 25-40, with optimum salinities of 30-35. This suggests that C. punctatum prefers relatively warm waters and an oceanic habitat for its growth and can adapt to significant changes of salinity levels. When C. punctatum was cultivated at different temperature and salinity levels, the PST profile included four major analogs (STX, neoSTX, GTX1 and GTX4, constituted >80 % of the profile), while low amounts of doSTX and traces of dc-STX and dc-GTX2 were also observed. Interestingly, though overall toxin contents did not change significantly with temperature, increases in the proportion of STX, and decreases in proportions in GTX1 and GTX4 were observed with higher temperatures. Salinity did not affect either toxin contents or profile from 25 to 35. However, the total toxin content dropped to approximately half at salinity 40, suggesting this salinity may induce metabolic changes in C. punctatum.

Bloom development of toxic dinoflagellate Alexandrium catenella (Group I) in Jinhae-Masan Bay, Korea: Germination strategy of resting cysts in relation to temperature and salinity.

To better understand the role of resting cysts in the outbreak of paralytic shellfish poisoning and bloom dynamics in Jinhae-Masan Bay, Korea, this study investigated the germination features of ellipsoidal Alexandrium cysts isolated from sediments collected in winter and summer under different combinations of temperature and salinity. Morphology and phylogeny of germling cells revealed that the ellipsoidal Alexandrium cysts belong to Alexandrium catenella (Group I). The cysts could germinate across a wide range of temperature (5-25 °C) with germination success within 5 days, indicating that continuous seeding for the maintenance of vegetative cells in the water column may occur through the year without an endogenous clock to regulate germination timing. In addition, the cyst germination of A. catenella (Group I) was not controlled by seasonal salinity changes. Based on the results, this study provides a schematic scenario of the bloom development of A. catenella (Group I) in Jinhae-Masan Bay, Korea.

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).