The Influences Of Silver Carp And Bighead In Bio-manipuation Pen On The Community Structure Of Crustacean

Lake Gehu, a typical shallow water, is located in the south of Jiangsu provincecrossing Wujin and Yixing, with a total area of164km2which just second to LakeTaihu in that region. It is situated at the economically developed Yangtze river deltaregion in China with developed water resources and variety functions of drink, shipping,irrigation, tour and aquiculture, et al. However recently, with the increasing nutrientloading rate in Lake Gehu, its ecological environment is under great damage. Manycurrent studies have showed that non-classical bio-manipulation, a way to prevent waterbloom and improve water ecological environment by controlling fierce fish andstocking planktonivorous filter-feeding fish (such as Hypophthalmichthys molitrix andAristichys mobilis), can be effective. However, as the dominated group of zooplanktonin fresh water worldwide, to some extent, the community structure of crustaceans areinfluenced by the different stocking patterns, fish density and lake type. In recent years,widely attention has been paid into the influences of Hypophthalmichthys molitrix andAristichys mobilis feed in pen on the lake ecosystems, of which the past domesticstudies were mainly focused on aquatic plants, physical and chemical factors, thecontrol of eutrophication, phytoplankton and benthonic animals, et al., however, fewrelated reports have been done in the bio-manipulation fish pen of Lake Gehu about theinfluences of filter-feeding fish and abiotic environmental factors on crustaceans, andthat is our work to fill in the blanks now. This study combined the water ecologicalmanagement of Ge canal basin to do research on the influences of Hypophthalmichthysmolitrix and Aristichys mobilis in bio-manipulation pen on the community structure ofcrustacean. Thus, from December2009to November2011, a large bio-manipulationfish pen with the stock of silver carp (Hypophthalmichthys molitrix) and bighead(Aristichys mobilis) inside was built to control the cyanobacterial bloom in Lake Gehu,and at the meantime, an investigation and laboratory analysis was carried out to compare the variation of the crustacean community structure among region A outside ofthe fish pen and regions B, D, C with different ratio of fish (1:4,1:2,1:1.5, respectively),which was combined to discuss relationship between crustacean and the specialenvironment, the effects on improving eutrophic water was also been involved, it canprovide scientific basis for the protection of ecological system in Lake Gehu and theecological aquiculture.The main results were as below:1.35species of cladocera, belonging to7Families,15Genera,25species ofcopepoda, belongs to8Families,15Genera, were identified in these four regions duringDecember,2009and November,2011, among which32species of cladocera,respectively in2010and2011. While the numbers of copepoda were24and22,respectively. The numbers of species varies with different season: the species ofcladocera got highest in spring, while species of copepoda were high in spring andsummer, low in autumn and winter.2. The dominated species of cladocera in2010were Bosmina longirostris,Ceriodaphnia cornuta and Moina sp, while Bosmina longirostris, Ceriodaphnia cornutaand Moina micrura in2011. The dominated species of copepoda in2010wereMesocyclops leuckarti, Schizopera neglecta, Sinocalanus dorrii, Cyclops vicinus vicinus,Limnocletodes angustodes, Eucyclops serrulatus, while Eucyclops serrulatus,Schizopera neglecta, Mesocyclops leuckarti, Sinocalanus dorrii and Limnocletodesangustodes in2011.3. The comparison of annual density and biomass of cladocer was A>C>D>B in2010, significant difference was showed between A and B, while A>D>C>B in2011.The comparison of annual density of copepoda was C>A>B>D, annual biomass wasA>C>B>D,4regions all showed three peaks, respectively with changes of months,while the two values were B>D>A>C in2011, each region showed highest value insummer, which had significant differences with other seasons.4. Diversity index: the annual values of H′、D and J of cladocera were1.027、1.167and0.620, respectively, while0.868、1.019and0.541, respectively in2011. Accordingto the comparison of4regions, H′value was highest outside of pen, with D and Jhighest inside of pen in2010, while three indices all showed highest outside of pen in2011. The annual values of H′、D and J of copepoda were1.025、1.181�'�0.701, respectively in2010, with0.860、1.043�'�0.667, respectively in2011. Three indiceswere all highest inside of pen in2010, while only H′value showed highest outside ofpen in2011.5. The cladocera and environmental factors: in2010, density and biomass showedhighly significant positive correlations with temperature, Chl.a and NO3-N, while highlysignificant negative correlations with transparency, H′showed highly significantpositive correlation with the former three environment parameters and TN, whilesignificant positive correlation with Chl.a; in2011, density and H′showed significantpositive correlations with Chl.a, as density also showed highly significant negativecorrelations with TP, according to CCA analysis in2010, temperature, CODMn、NO3-N、SD were the main abiotic environmental factors affecting the density of cladocera.The copepoda and environmental factors: in2010, density and biomass showedhighly significant positive correlations with TN, NO3-N, temperature and Chl.a, whilehighly significant negative correlations with TP and transparency, H′showed highlysignificant positive correlations with DO, while significant negative correlations withCODMnand Chl.a; in2011, density showed highly significant positive correlations withTN and Chl.a. According to CCA analysis in2010, temperature was the most importantfactor affecting the abundance of copepoda, and CODMn, DO, NO3-N, TN, NH4-N,transparency, depth of water and TP were the factors listed here followed by theirinfluence degrees.6. In August, the density of Moina sp. in region A had significant differences withregion B and D, while3regions inside of fish pen had no apparent differences, et al.,the results of which indicated that Moina sp. with a larger volume may be easier to bepreyed by fish than the other two small species.7. About the effects of bio-manipulation pen: the annual Chl.a value outside of fishpen in2010was higher than the value inside of fish pen with a significant difference,there were amounts of algae group floated on the water outside while relatively lowerinside of fish pen, combined with the comparison of species diversity, it was consideredto be effective to some extent, however, the best stocking biomass ofHypophthalmichthys molitrix and Aristichys mobilis and proportion between them stillneed further investigation and study.