Changshan Archipelago in the North Yellow Sea, the center for scallop Patinopecten yessoensis farming, is the second largest group of islands in China. In this study, twenty-five top sediment samples were collected from this area(E122.225°-123.287°, N38.973°-39.439°)in October 2007 to investigate the distribution of dinoflagellate cysts.
Samples were sonicated and then sieved through 80 μm and 20 μm metallic screens, and the target materials were captured for observation. Forty six different morphotypes were observed. The number of species was close to that in Daya Bay and higher than any other sea areas in China. The Gonyaulacoid group was the dominant group with a proportion of 27.7%. The Protoperidinium group was the second most abundant group with a proportion of 25.5%. Among the species, Pentaphasodinium dalei and Warowia rosea were founded for the first time in China. The number of dinoflagellate species ranged from 7 to 20 among stations. Alexandrium tamarense and P. dalei cysts were most common. The former was detected in all stations, and the latter was found in all except station 9 and 10. The Shannon-Weaver diversity index (H') varied from 2.4 to 3.4. Compared to other sea areas such as Changjiang Estuary, Zhelin Bay and Shenzhen Bay, cyst concentration in Changshan Archipelago was relatively high. Cell densities of dinoflagellate cyst at each sampling site varied from 182 to 2960 per gram of dry weight (DW), with an average of 1201cysts/g DW. A. tamarense and P. dalei were dominant at all stations and contributed significantly to the abundance of cysts. At station 6, 8, 12 and 18, percent abundance of P. dalei and A. tamarense were 21.3%-43.6% and 13.1%-21.3%, respectively. Some harmful species such as Alexandrium affine, Lingulodinium polyedrum, Scrippsiella trochoidea and Gymnodinium catenatum were also observed. Sediment type is considered as the most important factor influencing the distribution pattern of dinoflagellate cysts.
A. tamarense, a paralytic shellfish poison producing dinoflagellate, distributed widely in the studied area. Its cyst density ranged from 14 to 829 per gram DW, with an average of 209. The concentration was higher than that of areas where harmful alga bloom events are frequent, such as Zhelin Bay, Shenzhen Bay and Daya Bay. A. tamarense cysts may have originated from central Yellow Sea where the cysts are abundant. These cysts might be transported to this area by the Yellow Sea warm current. The existence of abundant live A. tamarense cysts in Changshan Archipelago area may be partly responsible for the shellfish poison found in P. yessoensis.