Responses Of Flea Macrophylla And Pseudomonas Spiny To Salinity Stress

The salinization of freshwater ecosystems caused by human activities and climate change is a global problem that threatens freshwater resources and aquatic organisms.There are many reasons for salinization,including agricultural production,sea level rise,river hydrological regulation,mining,and the application of road deicing salt.Among them,the increase in salinity of freshwater ecosystems caused by the widespread use of road deicing salt has attracted more and more attention from society.The salinity intrusion of freshwater ecosystems in low-lying coastal areas poses a major threat to aquaculture and agricultural production.Phytoplankton is the primary producer in the ecosystem,and its number,composition,and population dynamics are largely affected by non-biological variables.Primary consumers who take phytoplankton as their main food will also fluctuate due to changes in water environmental factors.Cladocerans,as typical filter-feeding zooplankton,are often used as the first choice for most juvenile fish and shrimp.At present,cyanobacteria blooms occur frequently in some freshwater ecosystems,and aquaculture waters are also affected by them.Therefore,cladocerans may face the dual stress of increased salinity and cyanobacteria blooms,and it is urgent to have a comprehensive and in-depth understanding of their consequences.Therefore,it is necessary to consider the impact of increased salinity on cladocerans during the eutrophication of aquaculture water,so as to provide certain basic data for further research on the impact of water environmental changes on other zooplankton communities in the future.In this study,the ecological model species D.magna and M.macrocopa as experimental materials.By comparing the differential responses of two species of cladocerans with different body sizes to salinity stress,we further studied the changes of key enzyme activities,the population characteristics of D.magna under salinity stress and the effects of different food quality.Statistics of the survival,development,reproduction,population,key enzyme activities and other parameters of cladocerans.The main findings are as follows:(1)Response of life history characteristics of D.magna and M.macrocopa to salinity stressThe increase in salinity has a significant negative impact on the survival,development and reproduction characteristics of D.magna and M.macrocopa.The specific manifestations are reduced survival time,delayed maturity time,reduced body size during first eggs and first brood,and decreased reproduction.The median effect salinity(EC₅₀)of the key parameter obtained by fitting the life history characteristic model of D.magna and M.macrocopa shows that different body sizes of cladocerans also have significant differences in response to salinity stress.The smaller the body size of cladocerans,the higher the sensitivity to salinity stress,and vice versa.The two factors of salinity stress and body size also had significant interaction effect on the overall performance of cladocerans.In addition,salinity stress is significantly more harmful to the reproduction of cladocerans than to survival.(2)Effects of salinity stress on population dynamics and key enzyme activities of D. magnaUnder salinity stress,individuals of D.magna show changes in key enzyme activities,that is,the increase of superoxide dismutase(SOD)activity related to oxidative stress response and the increase of sodium potassium ATPase(Na⁺-K⁺-ATPase)activity related to osmotic pressure regulation.Whether it is the D.magna individuals of the life history characteristics or the change characteristics of their key enzyme activities,they are all related to the dynamic changes of populations,which are reflected in the decrease of the population growth rate(r)and the decrease of the carrying capacity(K),which ultimately leads to a decrease in population density.(3)Effects of different quality foods and salinity on the life history characteristics of D. magnaResults showed that both different quality of food and increased salinity had significantly negative effects on key life history traits and clearance rate,and the two factors also had a significant interaction on the survival,development,and reproduction of D.magna.The maximum values(J_max)of the key life-history traits and clearance rate,the median effect salinity(EC₅₀),and the optimal salinity(X₀)derived from the models showed that the survival,reproduction,and clearance rate of D.magna were threatened by high salinity,which were exacerbated by the presence of toxic Microcystis aeruginosa in food quality,but lower salinity was beneficial to D.magna to resist toxic M.aeruginosa.In conclusion,increasing salinity has effects on cladocerans individual,population and the activities of key enzymes,and these effects fluctuate with different food quality.This study will improve our understanding of the effects of increased salinity in aquaculture waters on cladocerans,and help to evaluate the availability of high-quality open feeds for juvenile fish and shrimp in aquaculture under environmental changes,and provide a basis for further research on the effects of environmental change on other zooplankton communities in the future.