Ecological Study On Phytoplankton Community In The Northern South China Sea

The characteristics of phytoplankton community in the northern South China Sea (nSCS) from2009to2011(cruises included summer, winter, autumn and spring) were studied in this thesis. Aim to know how to effected the marine phytoplankton community with the change of environment in ecology, and applied base materials for ecosystem protection in this area.The major results were as follows:a total of333phytoplankton species were identified (included variety and form) through collected samples from4seasons,182species of bacillariophyta,144species of pyrrophyta,3species of cyanophyta and4species of chrysophyta were included. Ebria tripartita belongs to undetermined phylum. Bacillariophyta and pyrrophyta were the main phytoplankton groups in the survey area, and trichodesmium spp. in the cyanophyta was also an important phytoplankton community group in the area. Species abundance and cell abundance of phytoplankton changed significantly between seasons.155species belonging to71genera of4phyla were identified in summer cruise (Jul-Aug2009) water samples.86species belonging to50genera of bacillariophyta,64species belonging to17genera of pyrrophyta,3species belonging to2genera of cyanophyta and2species of chrysophyta. The cell abundance of phytoplankton ranged from (0.16-6001.78)×103cells/L, the average cell abundance was26.49×103cells/L, bacillariophyta and pyrrophyta were taken25.81×103cells/L and0.67×103cells/L, respectively. The dominant species in summer were Thalassionema nitzschioides、Pseudo-nitzschia delicatissima and Gymnodinium spp., etc. The highest average cell abundance of phytoplankton appeared in5m layer in all layers. Phytoplankton cell abundance had a rapid decline from inshore to outward in5m layer, and the high cell abundance area were mainly located in the eastern part of Guangdong inshore and eastern Hainan Island inshore. It showed a " patchiness" pattern in transection A, a higher biomass of phytoplankton was located in the area of inshore besides Trichodesmium spp. appeared in two offshore stations.174species belonging to64genera of4phyla were identified in winter cruise (Jan2010) water samples. Bacillariophyta were predominant and coexisted with pyrrophyta, cyanophyta and chrysophyta. The cell abundance of phytoplankton ranged from (0.08～37.52)×103cells/L, and the average cell abundance was2.69×103cells/L, in which bacillariophyta and pyrrophyta were taken2.49×103cells/L and0.19×103cells/L, respectively. The dominant species in winter were Thalassionema nitzschioides、Thalassionema frauenfeldii、Chaetoceros messanensis and Thalassiothrix longissima, etc.50m layer had the highest average cell abundance of phytoplankton. A high phytoplankton cell abundance appeared in the inshore of the Pearl River Estuary and the central basin area in5m layer. It was complex that phytoplankton cell abundance distribution in the A transection, there were three high cell abundance stations, and it attributed to high cell abundance of bacillariophyta.182species belonging to74genera of4phyla were identified in autumn cruise (Oct2010) water samples. Totally included and132species (57genera) of bacillariophyta,44species (12genera) of pyrrophyta,2species (2genera) of cyanophyta and4species (3genera) chrysophyta. The cell abundance of phytoplankton ranged from (0.1～106.22) X103cells/L, and the average cell abundance was4.74×103cells/L, in which bacillariophyta and pyrrophyta were taken4.67×103cells/L and0.03×103cells/L, respectively. The dominant species in autumn were Thalassionema nitzschioides、Navicula spp、Skeletonema costatum、Chaetoceros curvisetus、 Guinardia stolterforthii and Paralia sulcata, etc. The highest average cell abundance of phytoplankton distributed in the surface (0m) in the all layers. The horizontal distribution of phytoplankton in5m layer showed a high cell abundance in northeastern of Hainan and inshore eastern of Guangdong, a similar characteristics of distribution with surface. Two high cell abundance of phytoplankton appeared in the25m layer at stations A5and A6in transection A were attributed to the distribution of Trichodesmium erythraeum and Chaetoceros curvisetus, respectively.175species belonging to75genera of4phyla were identified in spring cruise (May2011) water samples, which included106species of51genera of bacillariophyta,66species of20genera of pyrrophyta,2species of2genera of cyanophyta and2species of2genera chrysophyta. The cell abundance of phytoplankton ranged from (0.05～5.91) X103cells/L, and the average cell abundance was0.58X103cells/L, in which bacillariophyta and pyrrophyta were taken0.51X103cells/L and0.05X103cells/L, respectively. The dominant species in spring were Thalassionema nitzschioides, Navicula spp.、Pseudo-nitzschia delicatissima、Chaetoceros spp., etc. Vertical profiles of cell abundance in survey area showed that a high phytoplankton biomass was concentrated in the75m layer. A high cell abundance distribution inshore of the survey area in5m layer. Phytoplankton cell abundance showed two high level areas (stations A9and A5) in transection A, and the cell abundance reached to2.52×103cells/L and3.87×103cells/L, respectively.The changes of phytoplankton average cell abundance was that Summer> Autumn> Winter> Spring. The changes of average of Shannon-weaver diversity index was that Autumn> Spring> Winter> Summer. The average of Pielou evenness index changes was that Winter> Summer=Autumn=Spring. And the average of species richness index changes was that Winter> Autumn> Summer> Spring.Statistics and distribution of Trichodesmium spp. cell abundance analyzed in4cruises. The results of Trichodesmium spp. water column cell abundance above75m layer showed that the maximum cell abundance appeared in the summer (the average cell abundance was10.40X103cells/L), and the minimum cell abundance appeared in the autumn (0.28×103cells/L). The average cell abundance was0.84×103cells/L and1.02×103cells/L in winter and spring, respectively.In addition, net-phytoplankton samples were analyzed in summer and winter.174species belonging to57genera of4phyla were identified in summer and157species belonging to54genera of4phyla were identified in winter.The average cell abundance of phytoplankton in summer and winter were0.06×103cells/L and0.36×103cells/L, respectively. The dominant species in summer were Thalassionema nitzschioides、 Rhizosolenia styliformis、Climacodium biconcavum and Pseudosolenia calcar-avis, etc, and in winter were Thalassionema nitzschioides-. Chaetoceros messanensis、Rhizosolenia styliformis and Coscinodiscus spp., etc. The maximal cell abundance of phytoplankton was located in the inshore of eastern of Guangdong. Trichodesmium thiebautii belonged to cyanophyta was commonly found at many survey stations and the maximal cell abundance reached to10.63×103cells/L in summer; The average cell abundance of Trichodesmium thiebautii was0.21×103cells/L in winter, and the maximal cell abundance of phytoplankton was located in several stations near the Pear River. Trichodesmium spp. became one of the most important species in summer and winter in this area.