Study On Annual Variation Of Phytoplankton Assemblage In The Xiaoqingdao, China

Annual phytoplankton assemblages were studied at Xiaoqingdao Island(coastal Yellow Sea connected to the Jiaozhou Bay) during 2003. Meanwhile, phytoplankton community structures of Xiaoqingdao were compared with a simultaneously investigation in the Jiaozhou Bay from 2003-2004. Furthermore, 70 years variation of phytoplankton in Jiaozhou Bay was also discussed. Based on theses works, we represented the change character and direction of phytoplankton in Jiaozhou Bay and the influence of phytoplankton assemblage of the outer Jiaozhou Bay on the phytoplankton inner bay.This paper is composed of there parts. The first studies the seasonal character of phytoplankton assemblage of coastal Yellow Sea connected to Jiaozhou Bay in the seawater aroud the Xiaoqingdao Island during 2003. The result showed that a total of 148 taxa from four phyla, Bacillariophyta(86 species), Pyrrophyta(58 species), Chrysophyta (3 species), Cyanophyta(1 specie) were determined. In general, the most important phyla were Bacillariophyta and Pyrrophyta on cell abundance and species richness. There are two peaks of phytoplankton cell abundance in a year in the seawater around the Xiaoqingdao Island: the primary peak occurs in February (130.71×103cells/L), the secondary peak occurs in September(79.02×103cells/L) and the low period occurs in spring(June) and autumn(November). Cell abundance in a year ranged from 0.13×103cells/L to 130.71103cells/L and the average abundance was 9.82±17.53×103cells/L(n=365). The peak of phytoplankton cell abundance in February was caused by the bloom of Thalassiosira nordensk?ldii. In spring, the dominant species was mainly composed of Prorocentrum gracile,Leptocylindrus danicus,Cylindrotheca closterium, then it changed to Chaetoceros curvisetus,Coscinodiscus sp.,Thalassionema nitzschioides in summer, and it changed to Coscinodiscus sp.,Paralia sulcata,Pleurosigma sp. In autumn, finally, it recovered to Thalassiosira nordensk?ldii , Skeletonema costatum , Thalassiosira rotula ,Thalassionema nitzschioides in winter. During this study, species sequence was very obvious along with the variation of temperature. This implies that the phytoplankton community of inner Jiaozhou Bay would be influenced heavily by the coastal Yellow Sea phytoplankton assemblages.The second part showed that the phytoplankton community of inner Jiaozhou Bay would be influenced heavily by the coastal Yellow Sea phytoplankton assemblage, based on the comparison of phytoplankton cell abundance between the inner bay and the outer bay.The third part studied the change of phytoplankton community structure since 1936. The result shows that phytoplankton species composition, cell abundance and dominant species have occurred an obvious change in 70 years. Although species composition is still dominated by diatom, the species numbers showed an obvious decline comparing with the historical data. The species numbers of Pyrrophyta showed an increase tendency. Dominant species showed an obvious change, some dominant diatom species replaced by other species. Few Pyrrophyta species rose up and became dominant species in Jiaozhou Bay. Dominant community is mainly composed of red tide species now.Based on these studies, the phytoplankton community of inner Jiaozhou Bay would be influenced heavily by the coastal Yellow Sea phytoplankton assemblages. Comparing with the historical data, phytoplankton species composition, cell abundance and dominant species have occurred an obvious change in Jiaozhou Bay. However the change of community is converse.