Community Structure Succession Study Of Phytoplankton And Sediment Diatom In Jiaozhou Bay

To know the effect of long-term variation of environmental factors on marine ecosysterm by studying the succession of phytoplankton community is one of the hotspot questions in marine science. This paper collected 70 years survey data of phytoplankton in situ in Jiaozhou Bay, carried a cruise during 2003-2004 to know the seasonal changes of phytoplankton in Jiaozhou Bay, and 15 days anchor days observation to know the effect of seawater change on the phytoplankton in August 2001, studied four dominant species growth feaiure of Jiaozhou Bay by culturing in lab., and analysed the diatom commnity characte:1 in sediment of Jiaozhou Bay. Based on these researches, we represented the succession character and direction of phytoplankton and sediment diatom in Jiaozhou Bay.This paper is composed of two parts. The first part studied the succession character and direction of phytoplankton in Jiaozhou Bay since 1936. The results showed that phytoplankton species composition, ;ell abundance and dominant speices 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, especially for the specie:; of Chaetoceros, Coscinodiscus and Rhizosolenia. The species numbers of pyrrophyta showed an increase tendency by Prorocentrum, Alexandrium and Scrippsiella trochoidea rose up. Dominant species showed an obvious succession, some dominant species replaced by other species. Dominant community is composed mainly of red tide species now. Few pyrrophyta species rose up and became dominant species in Jiozhou Bay. The cell abundance of net-phytoplankton showed a decline tendency under the eutrophicated effects. Silicate limitation, higher grazing pressure and mixture of tide are considered the main reasons that leading to the decline of cell abundance. Comparing with the historical data, the diversity index of phytoplankton in J aozhou Bay also showed a declinetendency. Thus, in the frame of globe climate change and human activity on nature, the phytoplankton community in Jiaozhou bay showed a tendency of succession that warm water species increase and cold water species decrease on temperate, and favored nitrogen species increase on nutrient physiology.The second part studied the succession of sediment diatom and signification on environmental change in Jiaozhou Bay. The results indicated that diatom composition, cell abundance and dominant species occurred an obvious succession in last century. The highest peak of diatom species and cell abundance appeared from 50's to 70's, and the lowest peak appeared from 80's to 90's. Pelagic diatom showed an obvious decline on cell abundance since 80's. Moreover, warm and eutrophicated species began to increase, and Cyclotella comta became dominant species replaceing of Coscinodiscus lineatus in sediment since 80's,. The succession of diatom was effected by salinity, water temperature and silicate limitation, and along the direction of warm species increase and large-cell species decrease. Otherwise, diatom cell concentration can reflect the historical accident in some extent.Based on these results, 80's were considered a watershed of phytoplankton and sediment diatom in Jiaozhou Bay. Data in situ and sediment indicated that pelagic diatom showed a decline tendency and dominant species composition simplified since 80's. Moreover, warm species and eutrophicated species increased after 80's. Globle climate warmed and silicate limitation were considered the important factors that effected phytoplankton community succession.