Structure characteristics of planktonic microalgae community in Litopenaeus vannamei shoal water culture ponds in western Guangdong

Planktonic microalgae in shrimp ponds play the role of primary producers,and have a major impact on material cycle and energy supply of the water ecosystem.The continual and regular surveys on the planktonic microalgae community were conducted in four Litopenaeus vannamai shoal water culture ponds at Guanlida Biotechnology Corporation in Dianbai,Maoming,Guangdong Province.Moreover,the community compositions of planktonic microalgae in shrimp ponds and their characteristics were analyzed.The results showed that a total of 91 planktonic microalgae species were identified during the culture period.Among them,30 species were Cyanophyta,15 were Chlorophyta,37 were Bacillariophyta,5 were Pyrrophyta,2 were Euglenophyta,and 2 were Chrysophyceae.The dominant species were Arthrospira platensis,Chlorella pyrenoidosa,Kirchneriella microscopica,Peridinium pusillum,Nitzschia closterium,Lyngbya gardneri,Oscillatoria chlorina,Oscillatoria salina,Nostoc microscopicum,Oscillatoria neglecta,and Oscillatoria willei.During the early culture period,the range of the quantities of planktonic microalgae,the biomass and the diversity index averages were 5.12×104～95.41×104ind/L,1.95～1.18×102μg/L,and 0.84～2.16,respectively.Chlorophyta and Bacillariophyta often appeared.However,in the middle and final phases,the averagesplanktonic microalgae density,the averages of biomass and the diversity index ranged in 66.11×104～1.28×109ind/L,13.3～11.87×103μg/L,and 1.64～2.87 respectively,and Oscillatoria gradually became the dominant species.The present study demonstrated that all the planktonic microalgae density,biomass and diversity index showed the same trend that they were generally low at the initial phase of the culture period and became high at the final phase.However,in mid-late July,the planktonic microalgae density and the physical and chemical factors in water fluctuated under the influence of severe weather conditions resulted from typhoon etc.