Diversity Analysis Of Phytoplankton In Offshore Water Of Jiangsu Province

According to the investigation in offshore water of JiangSu province from July2006to November2007, the species composition, which were mainly the species composition, distribution of cell abundance, dominant species, community diversity and community structure seasonal variation of Phytoplankton. thes results are summarized as follows:A total of186species which belong to68genera of6phyla were identified from4cruises,including Bacillariophyta(151species of47genera), Pyrrophyta(16species of7genera), Cyanophyta(4species of3genera), Chrysophyta(4species of3genera), Chlorophyta(9species of7genera), Xanthophyceae(1species of1genera). The maximum of percentage in cell abundance of diatom was in summer(July to August2006), The average of cell abundance of phytoplankton were4.98x106ind/m3,the average of cell abundance of Bacillariophyta were4.63×106ind/m3. The minimuman of percentage in cell abundance of diatom was in winter(from December2006to January2007), The average of cell abundance of phytoplankton were8.52x104ind/m3, the average of cell abundance of Bacillariophyta were8.29×104ind/m3. The average of cell abundance of phytoplankton in Spring(April to May2006) and Autumn (September to October2007) were5.91×105ind/m3and1.88×106ind/m3respectively, The average of cell abundance of Bacillariophyta were5.80×105ind/m3and1.63×106ind/m3respectively.The investigation indicated that Bacillariophyta is the dominant in cell abundance and species richness.The dominant species show seasonal variation apparently. The dominant species were Coscinodiscus radiates, Coscinodiscus oculusiridis, Coscinodiscus granii, Coscinodiscus asteomphalus, Skeletonema costatum, Rhizosolenis setigera, Chaetoceros lorenzianus, Ditylum brightwellii, Streptotheca thamesis, Thalassiothrix frauenfeldii, Thalassionema nitzschioides, Nitzschia pungens, Ceratium fusus, Ceratium tripos in spring. Coscinodiscus radiates, Coscinodiscus oculusiridis, Coscinodiscus granii, Coscinodiscus asteomphalus, Skeletonema costatum, Rhizosolenis setigera, Chaetoceros lorenzianus, Ditylum brightwellii, Streptotheca thamesis, Thalassiothrix frauenfeldii, Thalassionema nitzschioides, Nitzschia pungens, Ceratium fusus, Ceratium tripos in summer. Coscinodiscus oculusiridis, Coscinodiscus granii, Coscinodiscus spinosus, Coscinodiscus jonesianus, Coscinodiscus asteomphalus, Rhizosolenis styliformis, Ditylum brightwellii, Nitzschia pungens, Ceratium fusus, Ceratium tripos, Oscillatoria sp. in autumn. Coscinodiscus radiates, Coscinodiscus oculusiridis, Coscinodiscus granii, Coscinodiscus asteomphalus, Rhizosolenis styliformis, Biddulphia sinensis, Ditylum brightwellii, Thalassiothrix frauenfeldii in winter. The dominant species were characterized by warm water and euryhaline affinity.The average value of the Shannon-Wiener index were2.41during four cruises. The peak of the Shannon-Wiener index occurs in summer and the average is2.62, the low period occurs in winter and the average is2.19. The average value in spring and autumn were2.35and2.47respectively. The average value of the Pielou evenness index were1.00during the year. The peak of evenness index occurs in spring and the average is1.12, The low period of evenness index occurs in summer and the average is0.87, The average value in autumn and winter were0.93and1.05respectively. The average value of the Margalef index were0.71during four seasons. The peak of Margalef index occurs in summer and the average is1.13, the low period occurs in spring and the average is0.49. The average value in autumn and winter were0.68and0.52respectively.The Pielou evenness and species richness show high value in autumn. It appears that the community structure in autumn is better than that in other seasons. The Pielou evenness in spring and winter are better than autumn while the species richness is not good enough.The result show that the biodiversity index and evenness in offshore water of JiangSu province were lower, whereas the dominance was higher. These were related to eutrophication of this region. Because of the influence of surface runoff, especially influence of the yangtzi rever, the region was eutrophicated, meanwhile, the species composition of the region was changed, declined in numbers and biodiversity index, it meanted that the eommunity strueture of Phytoplankton became retrogression, and the biodiversity and evenness decreased.