Changes in algal phase and water quality following inoculation of microalgae in shrimp ponds in north-western saline areas
[Objective]In order to understand the changing patterns of microalgal communities in ponds used for the culture of Litopenaeus vannamei in northwestern saline areas,the effects of inoculation with Oo-cystis lacustris and Chlorella vulgaris on the algal phase and water quality of the ponds were investigated.[Method]The control group was not inoculated with algae and the treatment groups A and B were inocu-lated with Oocystis lacustris and Chlorella vulgaris respectively at a concentration of 2 mg/L depending on the volume of water in the pond.Three ponds were managed identically except for algae inoculation and three samples were taken every 5 d for microalgae quantification,multiplex analysis,community structure analysis and correlation between physical and chemical water quality factors and microalgal community structure.[Result]During the incubation period,the control group had a cyanobacterial outbreak with the highest Cyanobacterial biomass value of 58.77 mg/L,while treatments A and B both had Cyanobacterial biomass below 11.13 mg/L and formed a stable Chlorophyta phase at a later stage.The mean values of the Shannon-Wiener diversity index for the control and treatments A and B were:3.89,4.66 and 4.02,respec-tively,and the mean values of Pielou evenness index were:0.69,0.83 and 0.72,respectively.The com-bined trend analysis showed that the microalgal diversity was better in the treatment group than in the con-trol group,and that treatment A was better than treatment B.Multivariate statistical analysis and consis-tency analysis of community structure showed that the stability of the microalgal community in the treat-ment group was better than that in the control group,and the difference in community structure between treatment B and the control group was significant(P<0.05).The BIOENV(Biota-Environment)analysis showed that transparency(rm=0.893)was the environmental factor that best explained the structure of the microalgal community as a single factor,while NH4+-N+NO2--N+transparency best explained the mi-croalgal community structure as a multi-factor combination(rm=0.893).Analysis of yields at the end of the culture showed that shrimp survival and yields were significantly reduced following Cyanobacterial out-breaks in the control group,and that the losses to the culture from Cyanobacteria were irreversible and se-vere.[Conclusion]This study found that inoculation of O.lacustris and C.vulgaris inhibited Cyanobacte-rial outbreaks and reduced the risk of cultivation in northwest saline L.vannamei culture ponds.C.vulgaris showed better inhibition of Cyanobacteria than O.lacustris and had a greater effect on algal phase than O.lacustris,while inoculation with O.lacustris resulted in better algal phase diversity.
northwest saline landLitopenaeus vannameiOocystis lacustrisChlorella vulgarismicro-algae community structurephysicochemical index of water quality
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