Abundance Of Cyanobacteria In Aquaculture Ponds And Competitive Predominance Of Bluegreen Algae With Different Environmental Factors

Pond culture is one of the main production methods of aquaculture in China,and it is also the main source of aquatic product supply.As a still water ecosystem with human interference,long-term production activities will cause imbalances in the ecosystem,and the explosive growth of cyanobacteria.The large-scale reproduction of cyanobacteria will not only reduce the output of aquaculture products,but also affect the flavor and taste of aquatic products.By inhibiting the growth of other organisms in the water and even producing cyanobacterial toxins,it endangers the security of the entire ecosystem.Therefore,it is of great significance to study the impact of environmental factors on the outbreak of cyanobacterial blooms in ponds and to reveal how cyanobacteria form a competitive advantage in the competition with other algae,which is of great significance for exploring the mechanism of cyanobacterial outbreaks and managing cyanobacterial blooms.In this study,phytoplankton samples and water samples from aquaculture ponds were collected in April,August and December 2021.Through quantitative analysis,principal component analysis and Pearson correlation analysis,the composition of phytoplankton in aquaculture ponds changed with seasons,and the to explore the impact of environmental factors on the succession of phytoplankton communities.In this study,phytoplankton samples and water samples from aquaculture ponds were collected in April,August and December 2021.By measuring the physical,chemical and biological indicators of the water body,and using the method of principal component analysis,the composition of phytoplankton in aquaculture ponds with seasons was studied.changes,and explore the impact of environmental factors on the succession of phytoplankton communities.On this basis,taking the common cyanobacteria species M.aeruginosa and the green algae S.capricornutum as the research objects,the effects of different nitrogen and phosphorus concentrations,p H,antibiotic concentrations and other environmental factors on the two species were analyzed.The effect of algal growth competition was analyzed,and the physiological activity,photosynthesis and oxidative stress of ciprofloxacin on two algae were analyzed by microscopic counting,chlorophyll fluorescence,nitrogen blue tetrazolium method,phenylpropanyl sulfate method and fluorescence quantitative PCR method.and related genes psb A and rbc L expression and DNA repair gene rec A expression.The purpose is to explore the main factors affecting the competitive growth of cyanobacteria,and to provide a theoretical basis for preventing and controlling the outbreak of cyanobacteria in ponds.The main research conclusions are as follows:（1）Three surveys of phytoplankton and main water quality factors were conducted in April,August and December 2021.A total of 58 species of phytoplankton were detected in6 phyla,51 genera,including 21 Chlorophyta,18 Cyanobacteria,14 Diatoms,2 Euglena and Dinophyta each,and 1 Chrysophyta.The phytoplankton cell density ranged from 3.31to 8.82×10⁶cells/L,and the biomass variation ranged from 22.08 to 37.69mg/L.The dominant species in April were Oscillatoria princeps,Microcystis aeruginosa,Scenedesmus acuminatus,and Pediastrum boryanum.The dominant species in August was aeruginosa Microcystis and Merismopedia tenuissima,the main dominant species in December are Microcystis aeruginosa and Navicula phyllepta of Diatoms.Shannon-weaver index ranged from 1.19 to 2.68,Margalef index ranged from 0.81 to 1.92,and Pielou evenness index ranged from 0.13 to 0.69.PCA analysis showed that TP、WT and p H were positively correlated in the environment of cyanobacteria abundance,and the abundance of green algae was positively correlated with Cl^-and Mg²⁺.（2）Among the treatment groups with different nitrogen concentrations,the growth state of M.aeruginosa and S.capricornutum was the best in the normal concentration nitrogen treatment group（247 mg/L）during monoculture,the specific growth rate（μ）and the maximum environmental capacity（K）.By analyzing the competitive inhibition parameters during co-cultivation,it was found that M.aeruginosa had the greatest competitive advantage in the low-concentration nitrogen treatment group（24.7 mg/L）.In the treatment groups with different phosphorus concentrations,the two algae had the largestμand K in the normal concentration phosphorus treatment group（7.12 mg/L）during monoculture,and M.aeruginosa in the high concentration phosphorus treatment group（71.2 mg/L）under co-cultivation conditions L)has the greatest competitive advantage.In different p H treatment groups,the two algae had the largestμand K in the normal concentration phosphorus treatment group（7.12 mg/L）under monoculture conditions,and the competitive advantage of M.aeruginosa in the p H=9 treatment group under co-culture conditions was the largest.（3）Under monoculture conditions,ciprofloxacin（CIP）in the 0.5μg/L treatment group has a growth promoting effect on M.aeruginosa and S.capricornutum.The intrinsic growth rate increased by 0.01 and 0.08,and the intrinsic growth rate increased by 0.28 and0.03.In the CIP≥5μg/L treatment group,the growth of M.aeruginosa was inhibited,and the specific growth rate and the maximum cell density decreased.By calculating the competitive inhibition parameters of the two algae under co-cultivation conditions,it was found that CIP would change the competition between the two algae.In the treatment group with CIP≤0.5μg/L,the competitive advantage of M.aeruginosa.In the 5μg/L treatment group,the competitive advantage of S.capricornutum was greater.（4）In the 0.5μg/L CIP treatment group,the growth of M.aeruginosa and S.capricornutum was promoted by increasing the content of chlorophyll a,photosynthesis efficiency,and antioxidant enzyme activity;PSII inhibits the growth of M.aeruginosa by causing damage,increasing oxidative damage,and inhibiting carbohydrate synthesis.The main factors affecting the explosive growth of cyanobacteria in ponds are temperature,nitrogen and phosphorus concentration,p H,etc.In the competition with S.It is beneficial for M.aeruginosa to form a competitive advantage.Therefore,in pond culture,it is necessary to pay attention to changes in environmental factors such as temperature,nitrogen and phosphorus concentration,and p H.