Research On Feeding Ecology Of Zooplankton In Prawn Cultivated Pond And Natural Waters

Using the seawater dilution technique, microzooplankion grazing impact onphytoplankton was experimentally studied in Xiamen prawn cultivated pond andXiamen West Harbor.Copepod gut pigment contents were measured and thefeeding of Acartia pacme was studied. The grazing pressure of microzooplanktonon phytoplankton and its excretion of nitrogen derived from phytoplankton wereestimated. The effects of food concentration and diurnal photo period on thefiltering and grazing rates A. pacific were discussed. The main results are showedas follows:1. In the prawn cultivated pond, the year-round phytoplankton apparent growthrate ranged between 0.181 ~1 .2888 d-1. The maximum showed in spring withthe average 0.9762 d-1. Microzooplankton grazing rate was 0.1276~1 .3241d-1and summer had the highest rate. The herbivorous rates of themicrozooplankton were between 33.2~895.1mgC/(m3.d), equal to18.38~73.40% of the phytoplankton stock. Microzoopfankion grazing pressureon the primary production was high (37.47%~604.70%). The resultsconfirmed the idea that microzooplankton is very important in controlling thephytoplankton population and plays an influential role in the energy andmaterial flow in the ecosystem of ecosystem prawn cultivated pond.Microzooplankton grazing on phytoplankton took on obvious season changes.Microzooplankton grazing rate was 0.578~1.3241 d-1 in summer and theaverage of three sampling positions is 0.9762 d-1, the highest among fourseasons. Winter had the lowest grazing rate, varying between0.2037~0.255d-1, and the average was 0.2379d-1. In spring, microzooplanktongrazing rate was much lower than phytoplankton apparent growth rate. Thesetwo rates nearly equaled each other in autumn, with microzooplankton grazingon 86%, 106% of the primary production. For the first time, the basic data3at l, ] Aq{i9l lf tftk Abstractwere provided about seasonaI changes of microzooplankton grazing onphytoplankton in the ecosystem of subtropical prawn cultivated pond.2. Excretion of phytopIanktonederived nitrogen by microzoopIankton in prawncultivated pond was 2.52~15.27mg/(m'.d), 3.46~32.40mg/(m'.d) and5.92~67.98 mg/(m'.d) for the three sampling stations, respectjveIy Excretionof tota1 nitrogen by microzoopIankton was 2.52~15.27mg/(m'.d),3.46~32.40mg/(m'.d) and 5.92~67.98mg/(m'.d) respectiveIy. Themicrozooplankton excretion of phytoplanktonederived nitrogen couldpotentiaIly suppIy 2.90%, 1.19%, 0.063% and 0.55% of phy'topIanklonnitrogen demand for spring, summer, autumn and winter respectiveIyExcretion of nitrogen by microzoopIankton was estimated for the first time inprawn cultivated pond through microzooplanklon herbivorous rates, providingthe basic data for building the model of materials and energy in cuItivating seawaters.3. ln naturaI waters (Xiamen West Harbor), phy'toplankton apparent groWth ratewas 2.447 d-1 and microzooplankton grazing rate was 0.2542 d-1 in spring.The herbivorous rate of microzooplankton was 35.24mgC/(m'.d). The micro-zoopIankton grazing pressure on the primary production was 24.57%, equaI to22.45% of the phytoplankton stock. The results showed thatmicrozoop1ankton could controI the quantity of phytoplankton in Xiamen westharbor, preventing the formation of algae bloom. Excretion ofphytoplanktonederived nitrogen by microzoopIankton was 2.14mg/(m'-d),which couId potentiaIIy supply 0.2% of phytoplankton nitrogen demand.Excretion of totaI nitrogen by microzooplanklon was 2.68mg/(m'.d).Compared with the results from prawn cultivated pond in spring,.microzoopIankion grazing pressure was lower in Xiamen West Harbor. Thepotential supply to phy'toplankion nitrogen demand was smaIl in bothecosystems.4. As the food concentration ascended from 3.65x104to 1 .73x10'ceIlS/cm', thefiltering rates of Acarfis pacta intended to descend[0.33~0.14cm3/(ind..d)],but its grazing rates tended to increase[206~12050ce1ls/(ind..d A. pachodidn't show sig...