滆湖控藻网围中鲢鳙对枝角类群落结构的影响

The influences of silver carp and bighead carp in bio-manipulation pen on the community structure of cladocera in Lake Gehu

为了研究控藻网围中鲢鳙对枝角类群落结构的影响以及对富营养化水质改善的效果,于2009年12月—2010年11月对滆湖控藻网围外A区和网围内B、D、C 3区(鲢鳙比分别为1∶4、1∶2、1∶1.5)枝角类的群落结构和部分水质特征参数进行比较,并结合二者探讨了控藻网围枝角类群落结构与环境变量的关系。经鉴定,网围内外共采集到枝角类32种,隶属于7科14属。研究表明,网围内外枝角类种类组成相似,A区枝角类的年均生物密度和年均生物量均高于网围内各区,且与B区存在显著性差异(P<0.05)。优势种主要为长额象鼻溞、角突网纹溞和裸腹溞属未定种。8月A区裸腹溞属未定种的生物密度显著高于B、D区,而网围内3区波动幅度不大,结果表明,体积较大的裸腹溞属未定种比其他两个小型种类更易受到鱼类捕食影响。典范对应分析(CCA)表明,水温、高锰酸盐指数、硝酸盐氮和透明度是影响枝角类丰度的主要非生物因素。

As a dominant group of zooplankton in fresh water worldwide,Cladocera plays an important role in the material circulation and energy flow of water ecosystem,and it is not only a consumer for small animals and algae,but also food for zooplanktivorous fish.Many current studies have showed that non-classical bio-manipulation,a way to prevent water bloom and improve water environment by controlling fierce fish and stocking planktonivorous filter-feeding fish（such as Hypophthalmichthys molitrix and Aristichys mobilis）,can be effective.However,to some extent,phytoplankton and community structure of cladocera may be varied with different stocking patterns,fish density and lake type.Lake Gehu,a total area of 164 km2 crossing Wujin and Yixing,is located in the south of Jiangsu province.In recent years,more attention was paid to the researches about the influence of H.ypophthalmichthys molitrix and Aristichys mobilis on lake ecosystems,of which the past domestic studies were mainly focused on aquatic plants,physical and chemical factors,the control of eutrophication and phytoplankton,however,no reports have been made in the bio-manipulation fish pen of Lake Gehu about the influences of abiotic environmental factors and filter-feeding fish on cladocera,and that is our work to fill in the blanks.Thus,from December 2009 to November 2010,a large bio-manipulation fish pen with the stock of silver carp（H.molitrix）and bighead carp（A.mobilis）inside was built to control the cyanobacterial bloom in Lake Gehu,an investigation and laboratory analysis was carried out to compare the variation of the cladoceran community structure between region A outside of the fish pen and regions B,D,C with different ratios of fish（1∶ 4,1∶ 2,1∶ 1.5）,which was combined to discuss the influences of bio-manipulation fish pen on cladocera and the effects on improving eutrophic water.Through the identification,32 species of cladocera,belonging to 7 families,14 genera were collected inside and outside of the fish pen where there were no differences between species,and the annual average density and biomass of region A were both higher than any region inside of the fish pen,having a significant difference（P0.05）with region B,respectively.The main dominant species were Bosmina longirostris,Ceriodaphnia cornuta and Moina sp..In August,the density of Moina sp.in region A had significant differences from region B and D,while 3 regions inside of fish pen had no apparent differences,et al.,the results of which indicated that Moina sp.with a larger volume was easier to be preyed by fish than the other two small species.Moreover,some characteristic parameters of water were investigated to depict the correlation between cladoceran and environmental variables.CCA（Canonical Correspondence Analysis）showed that water temperature,permanganate index（CODMn）,nitrate nitrogen（NO3-N）and water transparency（SD）were the main abiotic factors affecting the community structure of cladocera.