Spatial And Temporal Distribution,Food Web Structure And Energy Sources Of Fish Communities In The Qingshitan Reservoir

Guilin is a world-class tourist city and one of the representatives of karst regions in the world,while the Qingshitan Reservoir is the largest drinking water source reservoir in the area.The study of fish community structure,food web structure and its energy source and ecological niche can provide theoretical support for fish resource conservation and ecological environment management.In this study,the spatial and temporal distribution of fish community structure,food web structure and its energy sources were studied from the perspective of different seasons（flood season and dry season）and areas（West Lake area and East Lake area）using carbon and nitrogen stable isotopes,statistical analysis methods,stable isotopes mixing model in R（SIMMR）and trophic ecological niche indicators.The main results are as follows:（1）A total of 3659 fish were collected,61978.17g,belonging to 28 species in 10 families and 13 genera in 4 orders.The number of Cypriniformes was the highest（64.30%）,and omnivorous fish（75.18%）dominated in number.The dominant species were Rhodeus ocellatus,Opsariichthy sbidens,Sinibrama macrops,Hemiculter leucisculus and Carassius auratus.Non-metric multidimensional scaling（NMDS）results showed that fish community structure was spatially significant（P<0.05）and seasonally insignificant（P>0.05）.The results of redundancy analysis（RDA）indicated that the environmental factors affecting fish communities were water depth and total phosphorus,which together explained 37.50%of the species relationships.（2）The trophic levels of fish consumers as a whole were clarified using nitrogen stable isotopes.The trophic level range of fish in the Qingshitan Reservoir was 1.83～3.26,which was low compared to other studies.The trophic level is related to the habitat,food source,as well as the fish’s own diets and individual size.（3）The spatial variation of fish food webs with different seasons was studied using carbon and nitrogen stable isotopes.Theδ¹³C values of epilithic algae,aquatic macrophytes,terrestrial plants,particulate organic matter（POM）and sediment organic matter（SOM）as carbon sources varied in range,indicating that the reservoir carbon sources varied with seasonal and spatial variation.Theδ¹⁵N of carnivorous fish varied with seasons;theδ¹⁵N values of fish in West Lake were higher compared with those in East Lake.（4）The SIMMR model was used to analyze the contribution ratio of energy sources of the dominant species of fish.The dominant species of fish relied on endogenous carbon sources dominated by aquatic macrophytes（26%～58%）during the flood season and exogenous carbon sources dominated by POM consisting of terrestrial plants（20%～74%）during the dry season.Aquatic macrophytes were the main carbon source for most dominant species of fish in West Lake（31%～73%）and East Lake（25%～31%）,which were contributed more to the dominant species of fish in West Lake.（5）The trophic ecological niche index was used to evaluate the trophic structure characteristics of the fish community.The trophic diversity of the fish community was higher in the flood season than the one in the dry season;omnivorous fish occupied the largest ecological niche space in both the flood and dry season;the overlap between the ecological niche of omnivorous fish and herbivorous fish was the highest in both the flood and dry season,indicating strong competition between them.The trophic diversity of the fish community in West Lake was higher than that in East Lake;the overlap of different feeding fish in East Lake was higher indicating that fish competition in East Lake was stronger;omnivorous fish occupied the largest ecological niche space in both lakes.