Seasonal Changes In The Dinoflagellate Cyst Flux And PSP Toxicity In Daya Bay, South China Sea

Sediment trap were set at the shellfish and fish cultural areas of Dapeng'ao area in Daya Bay, Southern China Seas from March 2005 to April 2006 to investigate the flux of dinoflagellate cysts. At the same time an investigation in PSP toxicity of these sea areas was carried on. The purpose was to understand the relationship between cyst flux of Alexandrium, abundance of its vegetative cells and PSP contents in shellfish tissues. This work revealed the resource of PSP toxin in this area, and helped to prevent PSP incident in the inshore aquaculture areas in Guangdong province.A total of 14 genera were identified in this study. They are Alexandrium, Lingulodinium, Protoceratium, Pyrophacus, Scrippsiella, Gonyaulax, Cochlodinium, Gymnodinium, Pheopolykrikos, Polykrikos, Protoperidinium, Diplopelta, Diplopsalis and Zygabikodinium. Scrippsiella trochiodea was the predominant cyst type almost in all samples. Alexandrium spp., as the most important PSP causative species in Chinese coasts, had been detected most of the year, but cyst flux was very low, normally under the number of 2×10⁴ cysts·m^-2·day^-1. Alexandrium vegetative cells occurred frequently and abundantly in winter, with the maximum abundance of 6×10 cells· L^-1, which resulted in high cyst fluxes with a maxima of 4.56×10⁴ cysts·m^-2·day^-1 occurring following the peak of vegetative cell.Results of the investigation on toxins showed that, PSP contents were normally below the limitation suggested by FAO of UN (80 μgSTX eq ·100g_Tissue^-1). The toxin in scallop ranged from ND(Not detect) to 260.02μg STX eq ·100g_Tissue^-1, with the mean of 35.69 μgSTX eq ·100g_Tissue^-1. Toxins in mussel was between ND and 1382.59μgSTX eq ·100g_Tissue^-1, with the mean of 46.09μg STX eq / 100g_Tissue. The toxin was higher in winter, and maximum occurred in shellfish aquacultural area in January, just after the peak abundance of Aexandrium vegetative cells and cysts. The toxins mainly accumulated in peptic of the shellfish, while no toxins were detected in other tissues of shellfish. The maximum toxin content was high up to 5156.50μgSTXeq ·100g_Tissue^-1. From the results, it could be suggested that abundance of vegetative...