| Planktonic microalgae as an important part of the primary producer in aquatic ecosystem, It has a close relationship between the water environment p H and the community composition of microalgae, p H is one of the important indexes for aquaculture and the comprehensive reaction of water chemical traits and life activities,it’s also an important ecological factor to effect the aquaculture activities. So a experiment of the relationship between community composition of microalgae and water quality factors was been investigated in saline Litopenaeus vannamei culture ponds where is in the Guangming Yuye co., Ltd(Dafeng City of Jiangsu province) form June 30 to October 06, 2014. According to the result of investigation, choose the dominant microalgae as the objects to study the relationship between the different microalgae and the water environment p H in different temperature and light intensity by means of orthogonal experiment. The purpose of this study is to investigate the correlation between different algae spices and water environment p H value, to explore the change laws of p H during the microalgae growth process.1. The community characteristics of planktonic microalgae and its relationship with water quality factors in Litopenaeus vannamei saline water culture ponds.According the investigation. The results showed that a total of 23 genera and 61 microalgae species were identified during culture period. Among them, 16 genera and23 species were Chlorophyta, accounted for 37.70% of the total species, 9 genera and16 species were Cyanophyta, accounted for 26.23% of the total species, 7 genera and 12 species were Bacillariophyta, accounted for 19.67% of the total species, 3 genera and 4species were Euglenophyta, accounted for 6.55% of the total species, 1 genera and 2species were Cryptophyta, accounted for 3.28% of the total species. Cyanophyta andChlorophyta were dominant microalgae during the breeding period, the dominan species of Cyanophyta were Anabaena flos-aquae, Microcystis aeruginosa, Microcystis firma and Raphidiopsis curvata. the dominan species of Chlorophyta were Oocystis borgei,Mougeotia laetevirens, Scenedesmus quadricauda and Crucigenia apiculata. the dominan species of Bacillariophyta were Cyclotella meneghiniana, Nitzschia longissima and Cyclotella comta. Besides, during the culture, the level of temperature was keep in24.0~29.5℃, ρchl-a in every ponds basically all showed significant positive correlation with p H value, CA, TN and TP, but negative correlation with the water transparency,NH4-N and NO2-N.2. A orthogonal experiment was designed to study the effects of 5 dominant species Microcystis aeruginosa and Anabaena sp. of Cyanophyta, Chlorella pyrenoidosa and Scenedesmus quadricauda of Chlorophyta, Cyclotella sp. of Bacillariophyta atdifferent temperature(20℃, 25℃and 30℃) and light intensity(2000lx, 4000 lx and 6000lx) on regulation of environment p H by the growth of Cyanophyta, Chlorophyta and Bacillariophyta. with no microalgae and just add the corresponding culture medium group as blank control. The results showed that:(1) The p H value of Cyanophyta medium was generally increased more than 9.00,with the growth of M.aeruginosa and Anabaena sp. under various temperature and light intensity. The p H value of Chlorophyta medium was in the range of 6.5~8.5, with the growth of Chlorella pyrenoidosa and Scenedesmus quadricauda under various temperature and light intensity. The p H value of Bacillariophyta medium was in the range of 6.5~8.5 with the growth of Cyclotella sp. The p H value of water environment was not significantly increase with the growth of Cyclotella sp. cells density, the p H nalue has been more stable after small increase in the first two days under various temperature and light intensity.(2) A highest p H value of M.aeruginosa medium was observed at 2000 lx and 25℃.Under such conditions, p H of M.aeruginosa medium could reach to the maximum value of 10.83 in ninth days and the maximum algal density could reach to 1.1×107cells/ml in tenth days. A highest p H value of Anabaena sp. medium was observed at 6000 lx and30℃. Under such conditions, p H of Anabaena sp. medium could reach to the maximum value of 11.02 in eighth days and the maximum algal density could reach to 2.2×107cells/ml in tenth days. A highest p H value of Chlorella pyrenoidosa and Scenedesmus quadricauda medium was observed at 6000 lx and 30℃. Under such conditions, p H ofChlorella pyrenoidosa medium could reach to the maximum value of 7.73 and the maximum algal density could reach to 8.1×106 cells/ml in tenth days. p H of Scenedesmus quadricauda medium could reach to the maximum value of 8.45 in ninth days, but the maximum algal density of Scenedesmus quadricauda could reach to2.3×106 cells/ml in tenth days at 6000 lx and 20℃. A maximum algal density of Cyclotella sp. was observed at 6000 lx and 30℃. Under such conditions, the maximum algal density could reach to 1.8×106 cells/ml in tenth days.3. Effect of different microalgaes on the water environment p HBy analysis of ANCOVA between the cells density of 5 microalgaes and p H value,it has positive correlation between p H and density of algae in water environment. The correlation coefficient R2 of p H and density of algae for M.aeruginosa is 0.904,R2 for Anabaena sp. is 0.801, R2 for Chlorella pyrenoidosa is 0.903, R2 for Scenedesmus quadricauda is 0.768, R2 for Cyclotella sp. is 0.576. The growth of Cyanophyta is much more likely to cause higher p H of the water than Chlorophyta and Bacillariophyta( P<0.01). The p H value show that Cyanophyta>Chlorophyta>Bacillariophyta under the same algae cell density. For different microalgae, the p H value show that Anabaena sp. > M.aeruginosa > Scenedesmus quadricauda > Chlorella pyrenoidosa >Cyclotella sp..In summary. During the aquaculture process, the community characteristics of planktonic microalgae has a closely relationship with the water quality. The p H value of water environment always increase when the microalgae outbreak, but the different microalgae has different effect. Among them, Cyanophyta played a leading role in promoting the p H increase. In this experiment, the p H value has increased significantly before the Cyanophyta blooms, then the p H value will be increased again when the Cyanophyta blooms. However, the p H value of Chlorophyta and Bacillariophyta lower than Cyanophyta, it indicated that mechanism of utility of inorganic carbon is different due to different contribution rate of p H in water environment. The results of this research may help regulate water quality in ponds for avoiding higher water p H by algae control, and provide as a reference for future study. |
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