Community Structure of Flagellates and Dynamics of Resting Cysts in Kamak Bay, Korea

Flagellates and their resting cysts were monitored monthly to investigate community structure and dynamics of red-tide causative organisms in Kamak Bay of Korea from May 1997 to June 1998. A total of 58 flagellate species were identified including 56 spp. of Dinophyceae and 2 spp. of Raphidophyceae. Standing crops of dinoflagellates were a maximum of 193,642 cells·l^(-1) in June 1997. Dominant species comprised Prorocentrum dentatum Stein in June 1997, and Prorocentrum minimum (Pavillard) Schiller and Ceratium furca (Ehrenberg) Clapare｀de & Lachmann from May to June 1998. A few species of Raphidophyceae appeared with very low standing crop only in the summer season in comparison with dinoflagellates.Resting cysts included 31 taxa of dinoflagellate cysts and one Chattonella cyst of Raphidophyceae. Cyst abundance varied extensively with spatial and temporal distribution; total cysts ranging from 457 to 1,048 cysts·㎝^(-3), and living cysts from 144 to 564 cysts·㎝^(-3). Living cysts constituted 25.0%-55.9% of total abundance and increased in the winter. The abundance of the living cysts showed a significant relationship to water temperature (r=-0.66, p=0.02) as well as to the seasonal variation of planktonic abundance in the water column. The vertical distribution of dinoflagellate cysts explained the process of eutrophication in this bay which has been accelerating for 40 years. Seventeen heterotrophic dinoflagellate cysts included 54.8% of total number of cyst species and their abundances comprised 50.4%-54.6% of total cyst abundance in inshore more than 29.0%-36.0% in offshore. This means that the composition ratio of the heterotrophic dinoflagellate cysts might be closely related to the eutrophication degree in such frequently red-tide occurring area. Seasonal dynamics of the Chattonella cyst seemed related to water temperature in view of the occurrence period of living cysts and empty cysts.