The Tendency Of Biodiversity Variation Of Phytoplankton In Pearl River Estuary

Phytoplankton is the most important primary producer in the estuary ecosystem, and also a basic link of marine food chain. It influences on the material circulation and energy flow. Phytoplankton biodiversity is closely related to marine ecosystem stability. According to data of April 2005,July 2005,April 2006 and August 2006 from ecological monitoring area about phytoplankton in Pearl River Estuary, the present situation of species composition,distribution,diversity of phytoplankton were analyzed and compared with the historical data, the changes of species number,cell abundance and diversity were discussed in mis thesis. The goal is providing some useful references for ecological environment protection and monitoring.The results showed that there were 99,155,85 and 102 species of phytoplankton during 2005 to 2006 base on four investigations. The most of them were diatom species, the secondly were dinoflagellate species. The dominant species were Skeletonema costatum,Pseudo-nitzschia pungens,Pseudo-nitzschia paradoxa,Chaetoceros curvisetus and so on.The average value of cell abundance of phytoplankton were 0.67×l0~4cell/m~3 and 19.78×l0~4cell/m~3 in April and July 2005, and were 2510.61×l0~4cell/m~3 and 3.12×l0~4cell/m~3 in April and August 2006, respectively. The ratio of highest and the lowest value is up to 9664.0, the horizontal distribution of cell abundance of phytoplankton was extremely imbalance. The lowest value of cell abundance appeared at Humen Estuary and Lingding Sea.The Shannon-Weaver index was ranged in 2.58 to 2.80, species evenness index was ranged in 0.50 to 0.62, species richness index was ranged in 0.81 to 1.34. The diversity level was not good, species-species distribution was imbalance, species number was not abundant enough in Pearl River Estuary, the dominant species were relatively higher in some sampling stations . Compared with the historical data, the results showed that the species number had decreased greatly from 244 in 1980s to 153 in 2006, namely, a decrease of 37.3%. Species composition changed obviously, the species number of diatom increased from the proportion of 70.1% in 1980 to 81.0% in 2006? the proportion of dinoflagellate reduced from 21.4% in 1980 to 8.5% in 2006. The annual variation of cell abundance was not significant, both diversity index and evenness index reduced slightly.In Pearl River Estuary, Salinity decreased sharply, the concentration of DIN and DIP increased greatly, eutrophication was serious, discharge of pollutants into Pearl River Estuary was increasing sharply. All of these induced the changes of phytoplankton species composition and diversity decrease.