Effects Of Microcysitis Aeruginosa On Interspecific Competition Between Daphnia Magna And D.pulex Or Moina Rectirostris

Global warming and water eutrophication are aggravating,resulting in frequent cyanobacteria blooms.Cladocera is the key component and dominant group of freshwater zooplankton community and is the link between primary producers and higher nutrient consumers in waters.The Eutrophication and the cyanobacteria bloom often lead to the decline of cladocera population of large zooplankton and are replaced by small cladocera.This study adopts the method of population cumulative culture and life table experiment,and takes Daphnia magna,Daphnia pulex and Moina rectirostris as the research objects that were used to study the results of interspecific competition between 2 species and 3 species of cladocera under different concentrations of Microcystis aeruginosa(0,5,10,20%,Scenedesmus obliquus+Microcystis aeruginosa,1.5mgC/L)and different initial densities of cladocera.In terms of life history characteristics,the effect of Microcystis aeruginosa on the outcome of interspecific competition among three cladoceras species with different individual sizes was explained.The main results are as follows:The results of interspecific competition between Daphnia magna and Daphnia pulex and Moina rectirostris were studied under the conditions of different concentrations of Microcystis aeruginosa and the initial density ratio of mixed culture.The results showed that with the increase of the concentration of Microcystis aeruginosa in food,the inhibitory effect on the population growth of them were enhanced,but the inhibitory effect on the population growth of Moina rectirostriswas relatively weak.The outcome of interspecific competition between Daphnia magna and Daphnia pulex depends on the initial density ratio of mixed culture,the higher the initial density ratio of Daphnia magna,the stronger the competitive rejection of Daphnia pulex;With the increase of the concentration of microcystis in food,the competitive inhibition of Daphnia magna to Daphnia pulex decreased.The outcome of interspecific competition between Daphnia magna and Moina rectirostris mainly depends on the quality of food.when the food contains microcystis,the competitive advantage of Moina rectirostris population will not be affected by their initial density ratio;The competitive inhibition of Daphnia magna to Moina rectirostris decreased with the increase of the concentration of microcystis in food and under different competitive experimental conditions,they can coexist.Between Daphnia magna,Daphnia pulex and Moina rectirostris,Daphnia pulex is at a competitive disadvantage when the food contains microcysts,while Moina rectirostris is in a competitive advantage and is not affected by their initial density ratio;The competitive rejection ability of Daphnia magna to Moina rectirostris depends on the concentration of microcysts in food and their initial density ratio.;The increase of the initial density ratio of Moina rectirostris weakens the competitive rejection of Daphnia magna to Daphnia pulex.The emergence of microcystis can change the competition outcome of Daphnia magna against Daphnia pulex and Moina rectirostris.It may be due to the differences in their adaptability to microcysts and their differences in individual size,resource utilization competition ability and anti-mechanical interference ability,resulting in the change of interspecific competition intensity.The effects of interspecific competition on the life cycle characteristics of Daphnia magna,Daphnia pulex and Moina rectirostris were studied under the conditions of different concentrations of Microcystis aeruginosa food and initial density ratio of mixed culture.The results showed that with the increase of the concentration of Microcystis aeruginosa in food,the first maturity time,first birth time and generation time of the three cladoceras were prolonged,and the net reproductive rate and intrinsic growth rate decreased.Under the food condition of microcystis,the competition of Daphnia magna inhibited the growth and reproduction of Daphnia pulex,prolonged its generation time and reduced its net reproductive rate and intrinsic growth rate.With the increase of the concentration of microcystis in food,the inhibitory effect of Moina rectirostris on the growth and reproduction of Daphnia magna was enhanced,the first birth time and generation time of Daphnia magna were prolonged,and the net reproductive rate and intrinsic growth rate decreased.In the interspecific competition of three cladoceras under different conditions,when the concentration of microcystis in food increased,the net reproductive rate of Daphnia magna,Daphnia pulex and Moina rectirostris decreased,and the competitive repulsive ability of Daphnia magna to Moina rectirostris decreased significantly.Affected by interspecific competition,the net reproductive rate of Daphnia pulex decreased significantly and the intrinsic growth rates of the three cladoceras decreased significantly with the increase of the concentration of microcystis.When the food contained microcystis,the intrinsic growth rate of Daphnia pulex was decreased with the increase of the initial density of Daphnia magna and Moina rectirostris,and the intrinsic growth rate of Daphnia magna decreased with the increase of the initial density of Moina rectirostris.The different effects of interspecific competition on the life history parameters of Daphnia magna,Daphnia pulex and Moina rectirostris may be due to their different adaptability to food resources and their individual size,resource utilization competition ability and anti-mechanical interference ability are different.It partly explains the competition and exclusion between large and medium and small cladocera under the condition of Microcystis aeruginosa and the decline of large population.