Distribution Of Dinoflagellate Cysts In Chinese Typical Coastal Areas And Its Relationships With Eutrophication And Algal Bloom

Distribution of dinoflagellate cysts in surface sediments from Chinese coastal waters was inverstigated, and 61 cyst types were detected during the survey, in which 14 morphotypes were first reported from the China sea. Cysts of toxic dinoflagellates, Alexandrium spp. and Gymnodinium catenation distributed widely but in low concentrations in most stations. A collection of illustrative plates of common cyst types in sediments collected from Chinese coastal sea areas were established by taxonomy study and characteristic description.Vertical distributions of cysts were studied in Daya Bay, Shenzhen Bay and Zhelin Bay, the South China Sea. The cyst assemblages recorded in about 20 cm sediment cores revealed the envirenmental changes and HAB records in the recent twenty years. Results indicated that the eutrophication was more severe resently, and the trophic levels from higher to lower were: fish cage areas, shellfish aquacultural areas, inshore areas and offshore areas, respecitively.Composition and seasonal distribution of cysts were studied from 2002 to 2003 and in spring of 2004 during a huge bloom of Prorocentrum donghaiense accompanied by Alexandrium sp. in Changjiang Estuary. Both cyst species richness and concentrations were higher in regions with higher longitude and lower latitude, where is more far away the river mouth. Low concentrations of Alexandrium cyst were analyzed in surface sediments during and after Alexandrium blooms, which suggested that cysts formed during the bloom did not settled and accumulated in the bloom area. It is supposed that these cysts of Alexandrium might move northward with diluted water of Changjiang River, and settled in the central area of the Yellow Sea.Scrippsiella trochoidea, the common HAB species of Daya Bay, had high efficiency to produce cyst. Moderate nitrogen depletion was favorable for its cyst formation. The germination rates were from 75% to 82%, and decreased obviously after stored under high temperature (25℃) and in long duration (over 30d). The dormancy period for S. trochoidea cysts was 15-25d. The results suggest that massive cyst formations results in a considerable loss of S. trochoidea population in the water column, which contribute to the collapse of algal blooms, whereas, the cysts supply rich "seed bed" for the occurrence of next bloom. Meanwhile the high germination rate and short dormancy period provide this species the ability to germinate and form blooms repeatedly in all seasons of the year in coastal areas of Guangdong Province. The PSP contents in shellfish were generally below the limit level suggested by FAO of UN (4 MU/g _tissue) in most samples, however an obvious peak value occurred in winter, and maximum of 72.2 MU/g _tissue was analyzed, just after the peak abundance of Aexandrium vegetative cells and cysts. The maximum cell density and cyst flux of Alexandrium were 603cells/mL and 4.56×10⁴ cysts/m² d, respectively. The toxins mainly accumulated in peptic of the shellfish, the maximum toxin content in peptic was high up to 350.4 MU/g _tissue. There were significant positive relationships between toxin level and vegetative cell density and cyst flux. From the results, it could be suggested that abundance of vegetative cells and cysts of Alxandrium influenced the toxin content directly and therefore resulted in the high winter level of PSP toxin in this area.