Annual Characteristics Of Plankton Communities At Yichang To Wuxue Section In The Middle Reach Of The Yangtze River

In order to reveal the community structure characteristics of plankton in the middle reach of the Yangtze river,in this study,surveys on the plankton communities were carried out at yichang to wuxue section(Yichang,Shashi,Jianli,Honghu,Wuhan,Wuxue)in the middle of the Yangtze River in April,July,November,2014 and January 2015(representing spring,summer,autumn and winter seasons),the main findings are as follows:1.Structure of the phytoplankton community(1)A total of 147 phytoplankton species belonging to 7 phyla were identified,among which there were 58 Bacillariophyta species,36 Chlorophyta species,24 Cyanophyta species,4 Euglenophyta species,3 Cryptophyta species,3 Tribonema species,2 Dinophyta species.As the seasons changed,the variation of phytoplankton was obvious.The quantity of species was the most in the autumn(92)and the least(46)in the winter.(2)The dominant species of the phytoplankton were Asterioncella.formsa,Synedra acus,Melosira granulata,Melosira granulata var.angustissima,Melosira varians,Fragilaria Capueina,Fragilaria crotonensis and Cyclotella stelligera in Bacillariophyta,Pediastrum simplex var.duodenarium in Chlorophyta,Phormidium tenu in Cyanophyta,Ceratium hirundinella in Dinophyta.(3)The mean density of the phytoplankton was 6.48×104ind./L,and the mean biomass was 1.33mg/L.Density and biomass of the phytoplankton consistent seasonal variation,was spring>summer>autumn>winter.Spring maximum(average density of 9.82×104ind./L,average biomass 2.01mg/L),the winter minimum(average density of 4.26×104ind./L,average biomass 0.78mg/L),density and biomass in spring and summer significantly higher than in autumn and winter.(4)The mean Shannon-wiener diversitv of the phytoplankton was 1.93,the mean Pielou diversitv was 0.57,and the mean Margalef diversitv was 3.65.Rusults indicated that the community structure of phytoplankton was stable,and the species distribution of phytoplankton was uniform.2.Structure of the zooplankton community(1)A total of 80 zooplankton species were identified,among wich there were 40 Rotifer species,13 Protozoa species,16 Cladocera species and 11 Copepoda species with a ratio of 50%,16.25%,20%and 13.75%,respectively.Species composition of zooplankton was different seasons.But Rotifer was dominant species in four seasons.(2)The dominant species of the zooplankton were Keratella valga,Keratella cochearis,Brachionus calyciflorus,Centropyxis discoides,Phryganella nidulus,Bosmina Baird longirostris,Sinocalanus sinensis.(3)The mean density of the zooplankton was 15.85×104ind./L,and the mean biomass was 0.57mg/l.The order of all stations' density of the zooplankton from large to little was:wuhan>wuxue>honghu>jianli>shashi>yichang,and it almost increased gradually from the upper to down of the river.The order of all stations' biomass was:wuhan>wuxue>honghu>shashi>jianli>yichang.In four seasons,the average zooplankton density and biomass in summer was the largest of all,second in spring,third in autumn and the least in winter.(4)The mean Shannon-wiener diversity of the zooplankton was 1.92,the mean Pielou diversitv was 0.56,and the mean Margalef diversity was 1.27.