The Characteristics Of Community Structure Of Phytoplankton And The Rotifer In Yangtze River Estuary

The hydrological environment of Yangtze River Estuary is complex and rich in biodiversity. Recently, it is important to research on the ecological problems in the Yangtze River Estuary due to the damage to the environment by human activities. This study of phytoplankton in the Yangtze Estuary was conducted from October 2010 to September 2011, September, December 2012, March, June 2013. And study on quarterly survey in the Yangtze River Estuary rotifer on March, June, September and December 2012. Through the study of phytoplankton in the Yangtze River Estuary and Rotifer Community Ecology, we elucidate the ecological characteristics of phytoplankton in the Yangtze River Estuary and rotifers so as to enrich the theory of Yangtze River Estuary ecological research. The main results are as follows:1. 311 species of phytoplankton were collected during two anniversary of phytoplankton in the Yangtze River Estuary, which belong to 8 phyla. The species number of Bacillariophyta is the most-219. The species number of Chlorophyta is 34, and there is 26 species of Cyanophyta, 12 species of Euglenophyta, 11 species of Pyrrophyta, 5 species of Xanthophyta, 2 species of Chrysophyta, and 2 species of Cryptophyta. In 2010-2011, we identified a total of 183 phytoplankton species(including varieties and forms), belonging to 7 phyla 60 genera, of which bacillariophyta was 137, and Chlorophyta is followed, which is 21 species. Besides there are 14 species of Cyanophyta, 4 species of Xanthophyta, 4 species of Euglenophyta, 2 species of Pyrrophyta and 1 species of chrysophyta. In 2012-2013 quarterly survey, we collected 231 species of phytoplankton(including undetermined species) totally, which belong to 8 phyla 83 genera. There are 161 species of Bacillariophyta, 25 species of Chlorophyta, 19 species of Cyanophyta, 11 species of Pyrrophyta, 8 species of Euglenophyta, 3 species of Xanthophyta, 2 species of Cryptophyta and 2 species of Chrysophyta.2. In 2010-2011 the dominant species were Skeletonema costatum and Melosira sulcate. Dominant specie in each month are diatoms in the most of time, but in March the Microcystis flosaquae and Oscillatoria amphibians are the dominant species, and in September a large number of Xanthophyta appear. In addition Dactylococcopsis rhaphidioides var. lciformis become the dominant specie in February, July and October. Investigation in the 2012-2013, the annually dominant species is Skeletonema costatum, and dominant species of each season is different. In fall dominant species are Skeletonema costatum, Lepocinclis sp., Pinnularia sp., Oscillatoria sp. and Navicula mollis. In winter the dominant specie are Skeletonema costatum and Nitzschia marine. In spring and summer; the dominant specie is only Skeletonema costatum.3. In 2010-2011 the density of phytoplankton in Yangtze River Estuary is between 2.83* 103 and 6.18*104cells/L.The highest density is in June and the lowest density is in January. The annual average density is 1.73*104cells/L. During 2012-2013, the phytoplankton density is between 3.26*105 and 8.22*105cells/L. The average density of phytoplankton in the four seasons is 5.362*105cells/L, the peak density of phytoplankton appeared in summer, while the lowest value appeared in autumn.4. In 2010-2011 the Pielou index of phytoplankton in March is the lowest and in January is the highest. Margalef index variations in 1.8-5.5. Shannon-Wiener index is between 1.6 and 3.4, the peak appears in February, and the minimum appears in March. In 2012-2013 Shannon-Wiener index of phytoplankton in Yangtze River Estuary variety 0.49-2.09. Margalef index is between 3.79 and 5.80. Pielou evenness index is between 0.09 and 0.39. The seasonal variation of diversity index is distinct. In autumn the diversity index are highest. In winter Margalef is the lowest. In the beginning of winter, Shannon-Wiener diversity index and Pielou’s evenness index decreased gradually and in the summer to reach the minimum value.5. CCA analysis results show that, in 2010-2011 phytoplankton can be divided into 6 groups. The dominant taxa in which there are Skeletonema costatum, Melosira sulcata, Cyclotella striata and Melosira granulata is the most important in the entire phytoplankton community structure obviously. The influence of this dominant taxa is great. This group is positively related with the temperature, and negative with turbidity. In 2012-2013 phytoplankton in Yangtze River Estuary can be divided into 4 groups, the dominant species Skeletonema costatum and Nitzschia marine are positively related with salinity and TSS. Lepocinclis sp.and Pinnularia sp. are negatively related with salinity and TSS. The distribution of phytoplankton in the Yangtze River Estuary area is mainly affected by temperature, salinity, TSS.6. In 2012, 23 species of rotifers were collected, belonging to 8 families. Among them there are 10 species of Brachionidae, 3 species of Trichocercidae. There are 2 species of Synchaetidae, Testudinellidae, Gastropodidae and Lecanidae respectively. Notommatidae and Asplanchnidae have 1 specie respectively. The Yangtze River Estuary rotifer species number reached a peak in autumn, and in winter is the lowest.7. In this study, polyarthra trigla is most common. In spring there are 5 dominant species of rotifer. The highest advantage degree of filinia longiseta, is 0.33. There are 7 dominant species in summer, polyarthra trigla advantage degree is the highest, reaching 0.37. There are 6 dominant species in autumn, polyarthra trigla advantage degree is 0.30, which is higher than the othesr. In winter, there are only 3 kinds. The highest advantage degree of Keratella cochlearis is 0.26.8. The average of rotifer density is 108.33 ind./L in Yangtze River Estuary. The highest density in spring was 231.33 ind./L, and the rotifer density decreased gradually. In autumn the density reaches minimum value, which is 35.33 ind./L.9. The Shannon Wiener index of rotifer is between 0.98-2.50. Pielou index is between 0.49-0.88 and Margalef index is between 0.53-0.94. The diversity index of rotifer in Yangtze River Estuary varied seasonally. Spring and summer is gradually increased and reach the highest in autumn, but in winter diversity index fall to the lowest.10 Through this study of phytoplankton and the rotifer in the Yangtze River Estuary, we find that phytoplankton and rotifer community appears to seasonal changes. In spring and summer it is phytoplankton and rotifer growth period. In addition, the temperature, salinity and TSS are the most important environmental factors in the Yangtze River Estuary.