A Preliminary Stady Of Changes In Plankton Community And Energy Utilization In Cobia High-level Breeding Ponds

Based on the data of ecological surveys made in May-June 2009 in two higher-level ponds of Guangdong ocean university's Science and Technology Park of Zhangjiang, analysis of the physical and chemical indexs of water, the species composition and changes of phytoplankton, the species composition of zooplankton; the relationship between phytoplankton and physichemical indexs has been analysised; analyze the relationship between the main environmental factors and primary production; analysis of the main environmental factors and analysis of the route of energy flow with energetics in ponds ecosystem. The main findings are as follows:1 Average value of each index during the trial period: water Temperature 29.7℃, Light Intensity 46KLux, Salinity 31.7, pH value 8.3, Secchi Disc depth 75cm, Total Suspended Solids 74mg·L^-1, Dissolved Oxygen 4.5mg·L^-1, Ammonia Nitrogen 0.15mg·L^-1, Nitrate Nitrogen 0.63mg·L^-1, Nitrite 0.045mg·L^-1, Phosphate 0.11mg·L^-1, Total Nitrogen 0.11mg·L^-1, TP 0.65mg·L^-1, N/P ratio of 10.27. According to available nitrogen, available phosphorus measured results, combined with the specific content of effective nitrogen and phosphorus, early phosphorus limiting factor to phytoplankton, phosphorus element can not be the restriction factor.2. 31 species of phytoplankton, which belonged to 15 genera of 3 phyla. Dominant species ascribing to Chlorophyta accounted for 51.61 percent and the quantity is 16 species belonging to 9 Genera; secondly the percentage of Bacillariophyta is 41.94 belonging to 5 Genera 13 species and the last of Cryptophyta is 6.45 percent belonging to 1 Genera 2 species. Average abundance of phytoplankton (AP) in pond A is 3489×10⁴ind·L^-1 from 1515-5910×10⁴ind·L^-1 and in pond B is 3896×10⁴ind·L^-1 from 2220-6260×10⁴ind·L^-1, overall average is 3963×10⁴ind·L^-1. Average weight biomass of phytoplankton (BP) is 6.46mg·L^-1 from 3.65-9.34mg·L^-1 in pond A and in pond B is 6.77mg·L^-1 from 4.13-9.88mg·L^-1, overall average is 6.63mg·L^-1. The total trend of AP and BP are earlier stage lower than later stage.The dominant species are Chlorella and Chlamydomonas. Average concentration of Chla is 26.93mg·m^-3, reached the maximum in the late breeding (26.93mg·m^-3).Analyse Shannon-Wieaver index, Simpson index and evenness index to phytoplankton, the results showed that three indices were slightly higher in pond A than in pond B, according to the evaluation criteria of diversity index, A pond showed moderately pollution, B pond showed moderately pollution on the beginning and serious pollution on the last. The biological indicators and chemical indicators of Pearson correlation analysis shows: the quantity biomass of phytoplankton, the density of phytoplankton, chlorophyll a and pH, TSS was very significantly positive correlation, and Transprancy was highly significant negative correlation. Phytoplankton biomass and light was significant positive correlation, chlorophyll a and phosphate was significantly correlated.3. 13 species of zooplankton were identified, among which there were protozoa 9 species, rotifers 2 species, copepod 2 species. The average biomass of zooplankton were 1.80mg·L^-1, of which protozoa had absolute dominance and the percentage was 88.6; the average weight of zooplankton were 1.80mg·L^-1, of which rotifera had absoluted dominance and the percentage is 52.7. The total trend of AZ and BZ are earlier stage higher than later stage.At the trend of daily variation, protozoa occupied the absolute partion in the quantity biomass, while at the weight biomass, rotifera occupied the absolute partion in earlier stage, copepoda occupied the absolute partion in middle stage, protozoa and artemia occupied the absolute partion in later stage.4. During the experiment, the average gross primary productivity of pond A is 5.81gO₂·m^-2·d^-1 and B is 6.98 gO₂·m^-2·d^-1, the average net primary productivity of pond A is 2.80gO₂·m^-2·d^-1 and B is 1.90gO₂·m^-2·d^-1.The average gross production and respiration ratio (P/R) in pond A is 1.98, higher than 1.38 in pond B. The distribution of phytoplankton primary production vertical change significantly. Gross production was significantly higher than the lower in upper, the highest level often appear in the surface layer. The distribution of respiration is relatively well-distributed, and not significant different in upper, middle and lower layer, the largest surface, followed by the bottom, middle minimum.By means of Pearson relevant analysis: the quantity biomass of phytoplankton, transprancy, TSS, light intensity and so on showed very significant positive correction to the gross primary production in pond A; the net primary production in pond A showed very significant positive correction to light intensity, and showed significant positive correction to Transprancy and TSS; the quantity biomass of phytoplankton, Transprancy, water temperature, TSS and so on showed very significant positive correction to the gross primary production in pond B, and the gross primary production showed significant positive correction to light intensity; the net primary production in pond B showed very significant positive correction to Transprancy and TSS, and showed significant positive correction to Chla, the quantity biomass of phytoplankton, TSS.During the experiment, the secondary productivity in pond A and B were zooplankton 0.46kJ·m^-2·d^-1, 0.65kJ·m^-2·d^-1; barancle 481.46J·m^-2·d^-1, 589.54J·m^-2·d^-1; zoobenthos 10.78J·m^-2·d^-1, 20.65J·m^-2·d^-1; fish production 17.88kJ·m^-2·d^-1, 24.26kJ·m^-2·d^-1, respectively. Respiratory oxygen consumption in pond A and B were fish 18078.06g, 13292.69g; barnacle 9528.06g, 11433.67g; water respiratory 78840.00g, 132732.50g; bottom respiratory 28890g, 38295g, respectively. During the test, sediment were 445.06kJ·m^-2·d^-1, 732.17kJ·m^-2·d^-1 in pond A and B respectively. Rotifers, Copeoods, Artemia salina and surimi were fed during the experiment, converted into the energy of the two pools were 2239.02kJ·m^-2, 3726.85 kJ·m^-2.Utilization rate of the solar radiation energy by the gross production of phytoplankton is 0.23% for pond A and 0.25% for pond B, respectively. The utilization of food energy is 20.77%,16.93% respectively. The food energy for unit kg fish is 24.15kJ,29.63kJ respectively. Clastic and bacterical accounted for 15.01% of the primary production in pond A and 18.02% in pond B, respectively. During the whole experimental period, without considering the drainage, there is 14.93% of the synthesized energy deposited in pond A, while 16.24% in pond B.