Characteristics of the evolutionary influence of the planktonic microalgae community survival on the Penaeus monodon's tidal shrimp culture

The present paper is involved with our study of the characteristics of the evolutionary influence of the planktonic microalgae community survival on the Penaeus monodon's tidal shrimp culture.For our research purpose,we have conducted the continuous and regular survey and observation on the planktonic microalgae community and water quality factors in Penaeus monodon's tidal culture ponds in Guanlida bio-technological corporation in Dianbai County,Guangdong,from May 19 to Sept.22,2009.The results of our investigation prove that a total of 93 planktonic microalgae species were identified during the culture period.Among them,26 species were recognized to be Cyanophyta,33 Chlorophyta,32 Bacillariophyta,with one belonging to Pyrrophyta,and another to Cryptophyta.The dominant species were of Navicula simplex,Chlorella pyrenoidosa,Oscillatoria chlorina,Cylindrospermum musiccola,Kirchneriella microscopica,Microcystis flos-aquae,Microcystis firma,Oscillatoria neglecta,Oscillatoria willei and so on.During the early culture stage,the range of the main species of planktonic microalgae,the biomass and the diversity index averages were identified at about 3.5×104-35.7×105 ind/L,0.02×102-1.83×102 μg/L,and 1.57-2.12,respectively.However,in the middle and final stage,the density,biomass and diversity of the planktonic microalgae prove to be in a range from 1.73×108-2.34×109 ind/L,5.23×103-57.01×103 μg/L,and 1.64-2.26 at the index average.In the culture process,it was found that with the gradual increase of the water temperature level,and that of TN and TP,the level of DO and the transparency of the water tends to decrease.The results of our investigation indicate that the planktonic microalgae density,the biomass and diversity index tend to reveal the same trend that they were generally low at the initial stage of the culture and then turned to be higher during the last stage.To be accurate,the microalgae density,biomass tend to show significantly negative correlation with the transparence,whereas highly positive correlation with the water temperature,the levels of TN and TP.The microalgae density,biomass in pond 1 and pond 2 particularly reveal highly significant positive correlation with the levels of TN and TP.And,in the final phase,there appears algal bloom in them,in which microalgae density turns to be over 109 ind/L.However,there appears a higher microalgae diversity in pond 3 and pond 4,which tends to reveal a positive effect on the improvement of the water environment.