| Yangcheng Lake is the third freshwater lake of Taihu plain; the total area of the lake is 119.04km2. It has a variety of functions such as fishing, farming, industrial water using, irrigation, tourism, shipping, and flood control. It also plays a unique role in conserving biological diversity and maintaining ecological balance. Aquatic plants are dense providing a food source for crabs and Yangcheng Lake yields high numbers of the Chinese mitten crab (Eriocheir sinensis). Currently, although the ecological effects of the pen culture on the environment has received extensive attention, they mainly focus on aquatic plants, physical and chemical factors, environmental effects and benthic animals, but rarely reported on the rotifer community structures.Micro-zooplankton community structure in 17 sites were investigated from January 2008 to December 2009, and investigated the rotifer community structure in 3 controlled sites in net-pen closing and lake areas of Yangcheng Lake during June 2008 to May 2009. Through statistical analysis of a large number of original data to analyze the micro-zooplankton community, temporal variation and species diversity indices, at the same time to analyze the relationship of micro-zooplankton community in different areas, in order to provide the basic data for the researching of the ecology of micro-zooplankton in freshwater ecosystem in Yangcheng Lake, and also provide the biodiversity conservation and sustainable development of ecological-pen-culture. The main results as below:1. Within a two-years of monitoring in Yangcheng Lake from 2008-2009, 237 species of protozoan were identified, which belonging to 3 classes, 96 genera. 111 species of rotifer were identified, which was belonging to 38 genera. The numbers of protozoan were higher in spring and autumn, and lowest in winter; the numbers of rotifer were higher in summer and autumn, lowest in spring.2. There were 28 dominant species of protozoan in 2008, and 23 in 2009. The top 6 of the species'dominance were all flagellates. There were 21 dominant species of rotifer in 2008, and 20 in 2009.3. The average annual density and biomass of protozoan were 226590ind./L and 2.212mg/L, respectively. The average annual density and biomass of rotifer were 2996ind./L and 7.51mg/L, respectively. Two of them all had seasonal variation, but not in the same trend. 4. The average value of H', D and J of protozoan were 1.832, 2.020 and 0.578, respectively. The average value of H', D and J of rotifer were 1.88, 1.51 and 0.76. The seasonal variation of H', D for both protozoan and rotifer were higher in summer and autumn, lower in winter and spring. But J had no significant seasonal variation.5. The density and biomass of protozoan both had significant positive correlation with TP, Chl-a, TSI; the density had a significant negative correlation with pH, but significant positive correlation with TN; the biomass had a significant negative correlation with transparency. The density and biomass of rotifer both had significant correlation with water temperature, Chl-a and TSI; the density had a significant correlation with pH, CODMn; the biomass had a significant correlation with TN and TP.6. Of the species recorded, 74 were pollution indicator species of protozoan, whichα-mesosaprobic species made up the largest share. 84 were pollution indicator species of rotifer, whichβ-mesosaprobic species made up the largest share. H', D and J of the micro-zooplankton indicatedα-mesosaprobic conditions. In the functional nutrition taxa of protozoan, the ratios of Photosnthetia qutotrophs and Algivores in 2009 higher than them in 2008, and the ratios of Bactivores-detritivors and the raptors were lower.7. The SJ of dominant species, density, biomass and J of micro-zooplankton had no difference among 3 lake areas and creeks of Yangcheng Lake. The density and biomass in east-lake were lower than the others, but the number of oligosaprobic species was the highest.8. The SJ of dominant rotifer species were higher among net-pen closings. The annual average of rotifer density and biomass in net-pen closings were lower than in lake areas.β-mesosaprobic species made up the largest share in all 6 sites. The ratio of oligosaprobic species in C1 was the highest, and the ratio of o-β-mesosaprobic species in A1 was the highest. The water analysis indicated that 6 sites were all eutrophication,β-α-mesosaprobic pollution, but a little lighter in C1 and A1. The crab culture didn't course the water pollution; on the other hand, some norms indicated that ecological-pen-culture can purify the water to a certain degree. |
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