Effects Of Fish Stocking On Plankton Community Structure In Wuliangsuhai Lake

In order to understand the ecological effect of fish stocking in Wuliangsuhai Lake,a one-year survey on plankton community structure was carried out in existing aquatic plants area and fish stocked area from July 2017 to April 2018.Meanwhile,we analyzed lake trophic status and water quality based on plankton.The main results are as follows:1.Eight phyla including 76 genera,154 species of phytoplankton in total were detected,142 species in existing aquatic plants area vs 88 species in fish stocked area.Species composition patterns were Bacillariophyta,Chlorophyta and Cyanophyta in existing aquatic plants area,while Chlorophyta,Bacillariophyta and Cyanophyta in fish stocked area.The average of Shannon-Wiener diversity index(H,)and Margalef richness index(D)in existing aquatic plants area were 4.29 and 4.23,respectively,which were significantly higher than those(2.46 and 2.30,respectively)in fish stocked area.A total of 26 dominant species were detected in Wuliangsuhai Lake,24 dominant species in existing aquatic plants area vs 11 dominant species in fish stocked area.The dominant taxon in existing aquatic plants area were Cyanobacteria,Chlorophyta and Bacillariophyta,while Cyanobacteria was the dominant taxon in the fish stocked area.The average density of phytoplankton in existing aquatic plants area(25.19×10~6cell/L)was significantly lower than that in fish stocked area(275.79×10~6 cell/L)(P<0.05),while the average biomass in existing aquatic plants area(13.34mg/L)was lower than that in fish stocked area(36.20mg/L),but the difference was not significant(P>0.05).Compared with historical data,phytoplankton community structure in existing aquatic plants area shows decline in phytoplankton diversity,the miniaturization of phytoplankton species composition and the dominant species shift to Cyanobacteria.Meanwhile,compared with existing aquatic plants area,fish stocking makes phytoplankton diversity decline,phytoplankton species miniaturize,and dominant species shift to inedible or rapid-growing species.2.72 genera,109 species of zooplankton in total were detected,88 species in existing aquatic plants area vs 67 species in fish stocked area.The average Shannon-Wiener diversity index(H,)and Margalef richness index(D)in existing aquatic plants area were 3.48 and 3.72,respectively,which were significantly higher than those(2.68and 2.85,respectively)in fish stocked area.A total of 26 dominant zooplankton species were detected in Wuliangsuhai Lake,20 dominant species in existing aquatic plants areas vs 14 dominant species in fish stocked areas.The average density of zooplankton in existing aquatic plants area(21749.89ind/L)was lower than that in fish stocked area(27125.24ind/L),but the average biomass(4.22mg/L)was higher than that in fish stocked area(3.34mg/L),even the differences between the two areas were not significant(P>0.05).Compared with the historical data,the zooplankton community structure in existing aquatic plants areas shows increase in zooplankton diversity,and the dominant species shift to protozoa.Meanwhile,compared with existing aquatic plants areas,the zooplankton diversity in fish stocked areas were declined,zooplankton species miniaturize,and the dominant species were replaced by protozoa and small rotifers.3.Evaluated based on plankton and Carlson index,the trophic status in existing aquatic plants area was light eutrophic.Evaluated based on phytoplankton density and Carlson index,the trophic status was heavy eutrophic in fish stocked area while it was mesotrophic-light eutrophic based on zooplankton biomass.The pollution state was moderate pollution in the two areas and have the trend of turning to severe pollution.