Zooplankton Community Structure And Its Relation To Environment Factors In Qiandao Lake

The Qiandao Lake, a large reservoir (artificial deep lake) in the lower reaches of theYangtze River, locates in Chun’an County, Hangzhou City, Zhejiang Province.Qiandaohu, it raised wide attention for the theory,which we called Aquatic enviromnentProtection oriented(AEPO)fishey. It also has arosen much controversy of domesticsociology scholars. The dispute at the moment revolves around whether intensepredation by planktivorous fsh should reduce the number of zooplankton and favor thedevelopment of phytoplankton and small-bodied zooplankton.Qian dao lake dominatedby big cladocerans--Daphnia hyaline from1999to2008,so sliver carp and bigheadcarp didn’t make the zooplankton smaller.Our aims of writing this paper were frst tostudy the temporal and spatial distribution patterns of zooplankton communitystructure and its relationship with the main environmental factors,and then to test thehypothesis that larger zooplankton size structure is associated with higher grazingpressure.The main results and conclusions are as follows: There are78species found in theresearch in2009and2010of which41species of rotifer accounts for52.6%of the totalnumber of zooplankton species, Among37kinds of plankton crustaceans, there are17species of Cladocera and20species of copepods, accounting for25.6%and21.8%respectively of the total number of zooplankton species. zooplankton speciescomposition monthly changes are obvious. rotifer species numbers were highest in mayand june; Cladocera species numbers were highest in july; copepod species numberswere very smooth whole year. in The spatial pattern showed that rotifer and Cladoceraspecies numbers were highest at upstream (S1) sampling site, middle reaches (S4),copepod species numbers were very smooth in three Sampling site.rotifer productionshowed two-peak in early spring (in april),and late summer (in september), Cladoceraproduction peaked in summer(in july or august), Occasionally,Higher production occurin april,may,june; copepod production were higher from late summer to winter.In termsof horizontal distribution, the rotifer production in S1and S4were higher than in S9,Cladocera production were very smooth in all Sampling site. Copepod production in S4and S9were higher than in S1.The vertical distribution of rotifer showed the productionpeaked at4m, Cladocera and Copepod production showed the production peaked at8mor12m, then decreased significantly during4~25m, and there were no obvious changesbelow25~50m; There are21taxa of zooplankton dominant species in qiandao lake, respectively,areKeratella cochlearis, Trichocerca similis, Trichocerca rousseleti, Trichocerca pusilla,Diurella stylata, Chromogaster ovalis, Pompholyx complanata, Polyarthra trigla,Synchaeta oblonga, Daphnia hyalina, Synchaeta oblonga, Bosmina longirostris,Diaphanosoma brachyurum, Diaphanosoma sarsi, Tropocyclops parvus,Microcyclops intermedius, Mesocyclops leuckarti, Thermocyclops taihokuensis,Thermocyclops hyalinus, Schmackeria forbesi, Neutrodiaptomus incongruens.Neodiaptomus schmackeri. Seasonal succession of dominant species of zooplanktonwere similar in S1and S4. Dominant species of rotifer (Keratella cochlearis,Chromogaster ovalis, Polyarthra trigla et al) peaked in spring, Dominant species ofsmall Cladocera(Bosmina longirostris,Diaphanosoma brachyurum et al) arised in latespring, peaked in summer; Dominant species of Copepod(Schmackeria forbesi,Neodiaptomus schmackeri) peaked in autumn and winter.Calanoida,Cyclopoida andnauplius production and rainfall had a significant positive correlation,while Cladoceraand rotifer production and rainfall hadn’t a significant correlation. Correlation betweenthree group zooplankton and physical and chemical factors showed that rotifer,cladocera, copepod production present a high relation with pH value, total nitrogen,total phosphorus,niate,nitite,silicateae.so zooplankton production were mainlydetermined by N,P,Si.Predation and competition are the main factors regulating population dynamies infreshwater organisms and also the most important structuring forces in freshwaterecosystems. The rotifer biomass and phytoplankton biomass had a significant positivecorrelation,The rotifer biomass present a negative relation with Cladocera monthly(except april),while presenting a positive relation with Calanoida and nauplius biomass,also present a negative relation with predator–Cyclopoida,so rotifer biomass weredetermined by phytoplankton and competition(Cyclopoida). The cladocera biomass andphytoplankton biomass had a significant positive correlation,but the cladocera biomasspresent a negative relation with rotifer biomass.The cladocera biomass present apositive relation with Calanoida and nauplius before september,but after septemberwere negatively.So the cladocera biomass was determined by abundent phytoplanktonbefore september,after september by competition from Calanoida. The Calanoidabiomass and phytoplankton biomass had a significant positive correlation, TheCalanoida biomass present a positive relation with Cladocera before september,butafter september were negatively.Because Calanoida’s capacity of competition was stronger than cladocera,so Calanoida peaked in autumn and winter. Calanoida weredetermined by Phytoplankton.At Qiandao Lake, from November2009to June2010, daphnia hyaline kept consistentwith phytophagous zooplankton rotifer, cladocera, nauplius and daphnia in time changetrend, and the positive correlation was found between daphnia hyaline and chrysophytaphytoplankton, so bottom-up effect played an important role in the quantity change ofdaphnia hyaline. However, from July to October, the average water temperature was20℃above, the density of daphnia hyaline reduced to minimum, which showed thatthe water temperature was the key factor in the quantity of daphnia hyaline. However,compared with historical data, the standing crop of daphnia hyaline positively correlatedwith the quantity of the phytoplankton and negatively correlated with the total quantityof silver carp and bighead carp. We found the peak of silver carp and bighead carp anddaphnia hyaline was at the different time, so the quantity of daphnia hyaline was mainlyaffected by bottom-up effect.From the quantity of silver carp and bighead carp and daphnia hyaline in1999,2004and from2007to2010, we concluded that the quantity of silver carp and bighead carpin1999was one fifth of the average in2004and from2007to2010, and the quantity ofrotifer and copepod kept invariant, daphnia hyaline decreased obviously which causedby the decrease of phytoplankton (conclusion6), so we inferred that the quantity ofzooplankton was not affected obviously by the culture of silver carp and bighead carp.