Fish Community Structure And Food Web Characteristics Of Xiliang Lake

Xiliang Lake is a typical shallow grass-type lake in the middle reaches of the Yangtze River,with various functions and benefits such as water supply to towns,flood diversion and storage,and biological habitat.In recent years,climate change,overfishing,purse-seine farming and other human activities have led to habitat fragmentation,degradation of water environment quality,changes in fish community structure and diversity,and changes in trophic relationships in the food web,affecting the integrity and stability of the water ecosystem.Fish are important consumers in the aquatic ecosystem,and the study of fish community structure and food web dynamics is an important way to understand the structure and function of the lake ecosystem and provide a scientific basis for the restoration and protection of the lake ecosystem.In this study,water environment and plankton surveys were conducted in Xiliang Lake in November 2020（autumn）,February 2020（winter）,April 2021（spring）and July 2021（summer）,and fish resource surveys were conducted simultaneously in November 2020and April 2021 to investigate the spatial and temporal characteristics of water environment and plankton,spatial and temporal changes of fish community and diversity,Changes in food web structure and trophic ecological niche dynamics.The main findings are as follows:（1）The submerged macrophytes in Xiliang Lake had significant spatial distribution differences,with more species and higher biomass in East-Xiliang Lake,including Potamogeton crispus,Vallisneria natans,Hydrilla verticillata,Ceratophyllum demersum and Myriophyllum verticillatum,and fewer species and lower biomass in West-Xiliang Lake.The results of water environment quality showed that under the spatial variation,the level of conductivity was higher in East-Xilang Lake,and the level of total phosphorus,ammonia nitrogen and permanganate index was higher in West-Xilang Lake;under the temporal variation,the level of conductivity was higher in spring,the level of chlorophyll a and water temperature was higher in summer,and the level of transparency was higher in autumn and winter.The results of redundancy analysis showed that turbidity,total nitrogen total phosphorus were important environmental factors affecting the phytoplankton community in Xiliang Lake;chlorophyll a were important environmental factors that nourished the zooplankton community in Xiliang Lake.（2）The fish community structure survey of Xiliang Lake showed that a total of12315 fish samples were collected,with a total of 31 species of fish belonging to 6orders and 8 families and 27 genera,of which Carpiformes were the most numerous（24 species）,accounting for 77.4%.Toxabramis swinhonis,Hemiculter leucisculus,Carassius auratus,and Cultrichthys erythropterus were the dominant species.The results of Nonmetric Multidimensional Scaling indicated the significant seasonal and spatial differences in fish community structure in Xiliang Lake（p<0.05）.Shannon-Wiener index,Simpson index and Pielou index of East-Xiliang Lake were significantly higher than that in West-Xiliang Lake in autumn（p<0.05）,and Margalef index was significantly higher than that in West-Xiliang Lake（p<0.05）;Functional richness index of East-Xiliang Lake was significantly higher than that in West-Xiliang Lake in autumn（p<0.05）,and functional dispersion index was significantly higher than that in West-Xiliang Lake（p<0.05）.Pearson correlation analysis exhibited that Shannon-Wiener index,Simpson index,Pielou index and Margalef index were significantly and positively correlated with functional richness index（r=0.66,r=0.61,r=0.50,r=0.83）and functional dispersion index（r=0.93,r=0.89,r=0.89,r=0.70）（p<0.05）.This result indicated that higher taxonomical diversity may contribute more functional space in fish assemblages.The results of fish functional shape found that the main contributing features of fish functional shape in Xiliang Lake were feeding habit,mouth position and maximum body length.The results of the Redundancy Analysis indicated that total phosphorus were the key environmental factors driving fish species and functional diversity,Total phosphorus was positively correlated with species number and Margalef index,negatively correlated with Simpson index,Shannon-Wiener index and Pielou index,positively correlated with functional evenness index,and negatively correlated with functional richness index,functional convergence index,functional dispersion index and functional redundancy index.（3）The results of carbon and nitrogen analysis of primary food sources in Xiliang Lake showed that in autumn,theδ¹³C values of phytoplankton,Particulate Organic Matter（POM）,plant detritus and Sediment organic material（SOM）were significantly different between lake areas（p<0.05）and theδ¹⁵N values of phytoplankton and POM were significantly different between lake areas（p<0.05）;in spring,theδ¹³C values of SOM were significantly different between lake areas（p<0.05）,andδ¹⁵N values of phytoplankton and SOM were significantly different between lakes（p<0.05）.The results of food source contribution indicated higher contribution of aquatic plants and phytoplankton in East-Xiliang Lake and higher contribution of phytoplankton and POM in West-Xiliang Lake.The structure of the food web shows that the horizontal structure has a greater span of food sources and the vertical structure has a longer food chain in the East-Xiliang Lake.The results of fish trophic ecological position showed that theδ¹⁵N range（NR）,Mean distance to centroid（CD）andδ¹³C range（CR）of the East-Xiliang Lake were greater than those of the West-West Liang Lake,indicating that the East-Xiliang Lake had a longer food chain length,higher trophic diversity of the fish community as well as a wide range of food sources and more available resources;the Mean nearest neighbor distance（MNND）of the East-Xiliang Lake were smaller than the West-Xiliang Lake and Standard deviation of nearest neighbor distance（SDNND）values were higher than the West-Xiliang Lake,indicating that the East-Xiliang Lake community had a higher degree of trophic redundancy,a stronger risk resistance of the ecosystem and a higher community,the higher stability of the community.