Studies On Fish Food Web Structure And Function Of Wanzhou Section And Xiaojiang River In The Three Gorges Reservoir

In order to identify the differences in fish community structure and function in the main stream of the Three Gorges Reservoir(TGR)and its tributaries after the normal operation of the Three Gorges Reservoir,based the values of stable isotope ratios and Ecopath model,the food web structure and function of aquatic ecosystem of two typical areas(the Wanzhou section in the mainstem of the TGR and the Gaoyang section in the Xiaojiang River)during the period of the two seasons(spring-summer,and anutmn-winter)of 2016 were studied in this study,and the main conclusions were obtained as follows:1)The fish resource surveys were conducted in the Wanzhou section located on the mainstream of the TGR and the Gaoyang section located on the Xiaojiang River which is one of tributaries of the TGR.The results showed that a total of 52 fish species belonging to 5 orders,9 families and 41 genus were collected in the two sampling sections during the whole sampling period.Of which,a total of 43 fish species belonging to 8 families and 35 genus were collected in Wanzhou section,and totally 42 fish species belonging to 9 families and 32 genus were collected in the Gaoyang section.There were 33 same species btween the two sections,and the Jaccard index was 0.63,indicative of the moderately similar in fish species between these two sampling sections.Moreover,there were 14 dominant species in the two sections and the main economic fishes consisted of small-sized fishes both the sampling sections.The fish species Tachysurus nitidus displayed the highest number proportions in the catches of the Wanzhou section,while the number of Hemiculter bleekeri was highest in the catches of the Gaoyang section.2)Zooplankton was the primary consumers of the lowest trophic level in Wanzhou section during the season of spring-summer.During this season,in Wanzhousection,the species which mianly feeding the secondary consumer were the carnivorous species,Culter alburnus displayed the highest trophic level and the fish species that the trophic level was greater 2.22 were gradually tansformed to be carnivorous species.For the Gaoyang section during the the season of spring-summer,zooplankton also was the primary consumers of the lowest trophic level,Parabotia bimaculata displayed the highest trophic level and the fish species that the trophic level was greater 2.45 were gradually tansformed to be carnivorous species.During the period of the autumn and winter,in Wanzhou section,Ctenopharyngodon idellus was primary consumers of the lowest trophic level,Coreius heterodon displayed the highest trophic level and the fish species that the trophic level was greater 1.70 were gradually tansformed to be carnivorous,while in Gaoyang section,Pseudorasbora parva was primary consumers of the lowest trophic level,Culter oxycephaloides displayed the highest trophic level and the fish species that the trophic level was greater 2.01 were gradually tansformed to be carnivorous.3)The food web structures and energy flows of trophic levels in Wanzhou and Gaoyang sections were estimated by use of the softeware Ew E.According to this model,the pathways of energy flow mainly included three ways in the Wanzhou section during the season of spring and summer,two of which were the grazing food chains,and one the detritus food chain,while the pathways of energy flow mainly contained two ways in the Gaoyang section during the same sampling period: one was detritus food chain which began from the debris;the other was the grazing food chain that started from phytoplankton.In autumn and winter,three pathways of energy flow could be found both the Wanzhou section and Gaoyang section,which included two grazing food chains and one detritus food chain.During the whole sampling period,the respiration quantities of the ecosystem mainly comed from the II trophic level,and the energy flow mainly flowed between the I and III trophic levels.The average transfer efficiencies of trophic levels II and III in Wanzhou section and Gaoyang section during the season of spring and summer were 2.73% and 3.09%,respectively,whlie in autumn and winter,the average transfer efficiencies of these two trophic levels in Wanzhou section and Gaoyang section were 3.21% and 3.69%,respectively.The average transfer efficiencies of these two sections during the two sampling periods were obvoulsy lower than the average values of other many similar reservior(10%).4)Based on the model of ecopath within the software Ew E,the Pianka method is used for estimateing the niche overlap.The results showed that during the seasons of spring and summer,the functional group Hypophthalmichthys and Cyprinus displayed the maximum prey overlap index and Shrimp and other fish species embodyed highest predator overlap index in the Wanzhou section,while both of Cyprinus and other fish species displayed maximum prey overlap index and maximum predator overlap index in Gaoyang section.Similiarily,during the seasons of the autumn and winter,Cyprinus and Carassius had maximum prey overlap index and predator overlap index in Wanzhou section,while Hypophthalmichthys and Carassius oth had maximum prey overlap index and maximum predator overlap index in Gaoyang section.5)Based on the model Ecopath,each functional group of aquatic ecosystems of Wanzhou section and Gaoyang section was ranked in descending order relying on the keystoneness index.During the seasons of spring and summer,pelteobagrus、zooplankton and other fish species were the keystone species of the Wanzhou section,while pelteobagrus、zooplankton and shrimp were the keystone species of the Gaoyang section.In the autumn and winter,pelteobagrus、zooplankton and shrimps and crabs were the keystone species of the Wanzhou section,while pelteobagrus、zooplankton and cyprinus were the keystone species of the Gaoyang section.Overall,the food web structures were relatively simple in 2016 in the Wanzhou section and the Gaoyang sections.The nutritional linkages among the species were weak,the energy flow path was short,and the proportion of nutrient recycling was low,representing the energy utilization efficiency was not high,indicating that the aquatic ecosystems of the two studied sections still remained in the state of an immature developed stage.