Studies On Community Structure Of Crustacean Zooplankton In Lake Yangcheng

Lake Yangcheng is the the third freshwater lake of Taihu basin, covers an area of119km2, which is an important water source of the Suzhou area and the onlypreparing source of drinking water for the city of Kunshan. Lake Yangcheng playsan important role in domestic water, industrial water, and irrigationand fisheries resources. Since the1980s, with the futher use of the water resources inLake Yangcheng, the nutrients are gradually enriched in the lake, which acceleratedthe eutrophication process of the lake. Algal blooms outbursted in Lake Taihu andother lakes in2007, all sectrs of society attach qreat importance to the safety problemsof water environment in resulting yeas. Lake Yangcheng which is famous forculturing high quality crab Eriocheir sinensis had a large area about13343.69acresfor the purse-seine aquaculture, in order to protect the ecological environment and thesource of drinking water,the government decided to reduce the area to about5271.58acres in2008. With the demolition of net in Lake Yangcheng,17sampling pointswere set to investigate crustacean zooplankton from January2008to December2009with a purpose to research the community structure and space distribution ofcrustacean zooplankton. We conducted a research about community structure,temporal changes and their relationship with environmental factors of the crustaceanzooplankton in Yangcheng Lake, and set points to analyze the differences inside andoutside of the pen about the crustacean zooplankton with a purpose to reveal whetherthe planktonic crustaceans of Yangcheng Lake has a response on the pen, andaccumulate data for the aquatic ecosystem variation of Yangcheng Lake and provide atheoretical basis for the sustainable development of the ecological fishery.The main results are sa follows:(1) Within a two-years of monitoring, there are21species of Copepoda in Lake Yangcheng, which belongs to16genera of7families. There are21species ofCopepoda in Lake Yangcheng, which belongs to17genera of7families. Copepodsand Cladocera shows a state of the eurythermal species, the northern species andsouthern species coexist together. The maximum of species number of crustacean zooplanktonoccurs in autumn, and the minimum occurs in spring.(2) The average annual density and biomass of Copepods were46.25±50.58ind./Land0.21±0.21mg/L, respectively. The average annual density and biomass ofCladocera were18.48±17.23ind./L and0.25±0.24mg/L, respectively. The densityand biomass in summer and autumn are higher than spring and winter. There is a clearseasonal variation between two years.(3) In2008, the density and biomass of Copepods in different lake regions varies from49.67-83.94ind./L and0.19-0.44mg/L, respectively, the maximum value occurred inwest lake and the lowest in riverway. In2009, it varies from15.95-36.93ind./L and0.082-0.15mg/L, respectively, the maximum value occurred in east lake and thelowest in middle lake.In2008, the density and biomass of Cladocera in different lake regions variesfrom5.15-42.09ind./L and0.073-0.70mg/L, respectively, the maximum valueoccurred in west lake and the lowest in riverway. In2009, it varies from4.90-24.54ind./L and0.060-0.30mg/L, respectively, the maximum value occurred ineast lake and the lowest in riverway.(4)The dominant species of crustacean zooplankton were Schmackeria forbesi,Limnoithona sinensis, Sinocalanus dorrii, Mesocyclops leuckarti, Thermocyclopsbrevifurcatus, Bosmina coregoni, Diaphanosoma brachyurum and Moina micrura.(5) According to the Pearson correlation analysis results, both the crustaceanzooplankton community density and biomass negatively related to the dissolvedoxygen, but both of then had a positive correlation with water temperature.(6) The average value of H, D and J of Copepods were1.13,1.04and0.65,respectively. The average value of H, D and J of Cladocera were0.69,0.74and0.43,respectively. As a whole showed a lower value.(7) The main physical and chemical character (TP, TN, SD and Chl.a), speciecomposition, density, biomass and the diversity Index inside the pen were notsignificantly different from those outside the pen.In conclusion, the blooming of algal and the pressure of fish predation have an influence on the growth and reproduction of large crustacean zooplankton, while infavor of small size species. The density and biomass of crustacean zooplankton in2009reduce much compared to2008. The water quality has improved. If the pen areacan be controlled within a certain range, the pen has no obvious impact on thecrustacean zooplankton.