The Characteristcis Of Phytoplankton Community And Water Quality Factors In High Producing Greenhouse Ponds Farming Litopenaeus Vannamei

In this study, the phytoplankton community composition and water quality factors in the ponds of greenhouse ponds Litopenaeus vannameifarming were characterized and their changes induced by water exchange were investigated.The primary findings were shown below.1. The characteristics of phytoplankton community and water quality factors in spring. From April to May, three ponds were randomly selected at a greenhouse pond farming Litopenaeus vannamei in Rudong, Jiangsu Province as sampling sites. The species composition, density and biomass of phytoplankton, and water quality factors were analyzed every 7 days. The results showed that the ammonia, nitrite, total nitrogen and COD increased as culture days increased. During the whole expiermental period, the water temperature ranged from 25.4℃ to 30 ℃, the salinity 6.4-10.8, the ammonia from 0.09-12.2 mg/L, the nitrite 0.002-2.474 mg/L, the total nitrogen 0.5-26.1 mg/L, the total phosphorus 0.12-1.37mg/L, the phosphate phosphorus0.01-0.27 mg/L, and the COD 37-184 mg/L. Regarding to phytoplankton, a total number of 31 gena belonging to 6 phyla were identified. Among them, 10 gena were Bacillariophyta, Chlorophyceae, and Cyanophyta had 10, 10 and 7 gena, respectively and accounted for 32.3%, 32.3% and 22.6% of total gena. The total density of phytoplankton ranged from 7.98×106 to 1.02×109 cell/L and the total biomass of phytoplankton ranged from 40.92 to 483.27 mg/L. The dominant specie were Cyclotella Sp. and Navicula Sp., and the Cyclotella Sp. was the absolute dominant specie in most time.2. The influence of exchanged water amount on the phytoplanktonic community composition. From August to October, the water in two groups of ponds(H1 and H2) was exchanged with new water at two different exchange rates, namely 3-5% for H1 ponds and 8-10% for H2 ponds. The phytoplankton community composition and water quality factors were analyzed every 7 days. The result showed a total of 33 gena belonging to 6 phyla were identified in H1 ponds and 35 gena belonging to 6 phyla were identified in H2 ponds. The common dominant species in both H1 and H2 ponds were Cyclotella Sp., Navicula Sp., Chlorella Sp., and Merismopedia Sp.. Microcystis Sp. and Chroomonas Hansg. Sp. became dominant species the middle and later periods in H1 ponds. Cymbella Sp. and Tetradesmus Sp. also became dominant species in H2 ponds. The Cyanophyta had been inhibited to some extent by the water exchange at high exchange rate.The density and biomass of phytoplankton in two groups of ponds were low in the early period, high in the middle period, and then reduced in the later period. The density and biomass of phytoplankton ranged from 360 to 178000×104 ind·L-1 and 0.94 to 159.37 mg·L-1, respectively in H1 ponds whereas 470 to 135000×104 ind·L-1 and 2.65 to 164.24 mg·L-1, respectively in H2 ponds. In the early period, the density of phytoplankton in H2 ponds were significantly higher than H1 ponds(P < 0.05), and the biomass of phytoplankton in H2 ponds were very significantly higher than H1 ponds(P < 0.01). There was no significant difference in density and biomass of phytoplankton between H1 and H2 ponds in the middle period. The density of phytoplankton in H2 ponds was significantly lower than H1 ponds in the later period(P < 0.01).