| The crustacean zooplankton mainly includes two major groups,namely,cladocera and copepoda,which are important component of lake ecosystems.On the one hand,crustacean zooplankton feed on bacteria and planktonic algae,and they are also natural baits for some fishes at the same time.Therefore,crustacean zooplankton plays an important role in the process of material circulation and energy flow in aquatic ecosystems.In addition,some species?e.g.Daphnia species?are important indicator organisms for water pollution,and their changes in community structure can better reflect long-term environment succession in the history of lake.In the middle and lower reaches of the Yangtze River,the largest freshwater lake group in China distribute here.In recent years,with the rapid development of industry and agriculture,these lakes have been polluted at different degrees,influencing the structure and function of aquatic ecosystems.In order to understand the community structure and diversity of crustacean zooplankton in the lakes located in the middle and lower reaches of the Yangtze River,the investigations were conducted during spring and summer in 2014-2016 in eight lakes which are Lake Donghu in Hubei province,Lake Chaohu,Lake Shengjin and Lake Nanyi in Anhui province,Lake Junshan,Lake Qinshan and Lake Yaohu in Jiangxi province,and Lake Taihu in Jiangsu province.The community structure,dominant species and density of crustacean zooplankton in each lake were studied.The relationships between the community structure of crustacean zooplankton and environmental factors were analyzed using the CCA method.Main results are as follows:1.In eight lakes located in the middle and lower reaches of the Yangtze River,a total of 12 families,23 genera and 30 species of crustacean zooplankton were identified,among which 6 families,13 genera and 17 species belonged to cladocera,and 6 species,10 genera and 13 species belonged to copepod.Bosmina,Diaphanosoma,Moina,Ceriodaphnia,Cyclops and Sinocalanus dorrii are dominant species in most lakes.Daphnia species are usually dominant species in spring in these lakes.2.In Lake Junshan,Lake Qinshan and Lake Yaohu in Jiangxi province,the densities of crustacean zooplankton ranged between 0.8-24.9 ind.·L-1,0.3-18.7ind.·L-1and 5.9-47.9 ind.·L-1,respectively.The density of crustacean zooplankton in Lake Yaohu was significantly higher than those in Lake Junshan and Lake Qinshan?P<0.01?.The densities of cladocera in the three lakes ranged between 0.5-23.4ind.·L-1,0.1-16.5 ind.·L-1and 2.8-40.8 ind.·L-1,respectively.Diaphanosoma,Moina micrura and Bosmina were dominant species of cladocera in summer in the three lakes whereas Daphnia galeata was dominant species in spring in Lake Junshan.The densities of copepod in the three lakes ranged between 0.2-10.5 ind.·L-1,0.2-2.3ind.·L-1and 3.1-23.0 ind.·L-1,respectively.Cyclops sp.was common dominant species in the three lakes.In Lake Chaohu,Lake Nanyi and Lake Shengjin in Anhui province,the densities of crustacean zooplankton ranged between 40.6-183.0 ind.·L-1,20.3-221.5 ind.·L-11 and0.6-129.4 ind.·L-1,respectively.Their maximum values(183.0 ind.·L-1,221.5 ind.·L-1and 129.4 ind.·L-1)appeared in July,August and June,respectively.The densities of cladocera in three lakes ranged between 31.3-153.3 ind.·L-1,6.9-163.2 ind.·L-11 and0.1-118.7 ind.·L-1,respectively.In Lake Chaohu,Daphnia similoides sinensis,D.galeata and Daphnia pulex were dominant species in spring whearas small cladoceras?e.g.Ceriodaphnia cornuta and Bosmina coregoni?were dominant species in summer.Bosmina,C.cornuta,Moina and Diaphanosoma were dominant species in Lake Nanyi and Lake Shengjin.The densities of copepod in the three lakes ranged between9.3-29.5 ind.·L-1,13.2-58.3 ind.·L-1and 0.5-10.8 ind.·L-1,respectively.Cyclops vicinus,Limnoithona sinensis,S.dorrii,Schmackeria forbesi and Mesocyclops leuckarti were dominant species of copepoda in Lake Chaohu,whearas Cyclops sp.,S.dorrii and Schmackeria inopinus were dominant species in Lake Nanyi.Gut content analysis showed that the food of Coilia ectenes was mainly composed of crustacean zooplankton?especially Daphnia species?in spring in Lake Chaohu.In Lake Taihu in Jiangsu province,the densities of crustacean zooplankton ranged from 7.4 to145.7 ind.·L-1,and the maximum value(145.7 ind.·L-1)appeared in May.The density of cladocera ranged from 1.9 to 131.5 ind.·L-1,and the dominant species were small eutrophic species,such as B.coregoni,Moina macrocopa and C.cornuta.The density of copepoda ranged from 5.5 to 24.2 ind.·L-1,and the dominant species was L.sinensis.In Lake Donghu in Wuhan city of Hubei province,the densities of crustacean zooplankton ranged between 1.0 and 8.5 ind.·L-1,the dominant species were also small eutrophic species?e.g.M.micrura and Diaphanosoma sp.?.3.According to the Shannon-Weiner index?H'?,the eight lakes located in the middle and lower reaches of the Yangtze River in this study had been polluted at different degrees.The Shannon-Weiner indexes?H'?of both Lake Qingshan and Lake Donghu were less than 1,belonging to heavily pollution.The Shannon-Weiner indexes?H'?of the other lakes was between 1 and 2,belonging to moderately pollution.CCA analysis showed that water temperature,nutrients?such as nitrogen and phosphorus?and chlorophyll a were important environmental factors affecting the community structure of crustacean zooplankton.Fish predation,dissolved oxygen,pH and transparency also influenced the community structure of crustacean zooplankton. |
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