Ecology And Toxicology Of Planktonic Protists In Semi-closed Mariculture Waters

The community and population dynamics of planktonic protists were investigated in a semi-closedmariculture waters for shrimp Penaeus japonicus in the suburb area of Qingdao. Nine of main environmental and biological factors were sampled, analyzed and presented. In addition, the functions of ciliated protozoa and removal of the harmful protozoan were also investigated using experimental and ecotoxicological method.Results reveal that (i) the variations of protist abundance and biomass follow seasonal cycle i.e. nonoplanktonic flagellates were the dominant fraction, mainly cryptophyceans during early spring, dinoflagellates during summer, chrysophyceans and chlorophyceans during autumn, while diatoms showed high summer blooms of nanoplanktonic centric genera and were very scarce during the other seasons, mainly with pinnate genera; (ii) the succession of functional-trophic groups follows the sequence of P-groupA-group-R-group and the sequence of B-group-P-group-A-group-B-group in pre-culturing stage and culturing, respectively; (iii) effects of shrimp culture on the succession of protist communities is considerably significant; (v) the protist abundance is considerably related to the assemble of five environmental factors (water temperature, ammonium-N, nitrite-N, nitrate-N and phosphate), while the protist biomass is related to two environmental factors (phosphate and bacteria); (iv) there are a closed relationship between the variation of chemical factors and the procedure of shrimp culture; (vi) 54 species (41 genus, 8 phylum) were examined, of which the dominants species consist of Teleaulax acuta, Hillea fusiformis, Pseudoscourfieldia marina, Gyrodinium spirale, Prorocentrum minimum, Prorocentnan rostratum, Tintinnopsis beroidea, Euplotes vannus and Mesodinium pupula, in which Prorocentrum minimum and Mesodinium pupula are red-tide forming species; (vii) it is available to monitor water quality of semi-closed maricuture biotopes using protists.Investigations on experimental ecology show that with the development of ciliate population the ammonium accumulation follows the model: ambient ammonium concentration reachs a peak in the logarithmic phase, drops sharply to a low level in the equilibrium phase and then exhibits a increasing trend in the decaying phase. The results demonstrate that ciliates can interrupt the normal population growth of bacteria, enhance breaking down organic pollutants and improving water quality. Therefore, it is suggested that ciliated protozoa play a posative role in improving and maintaining water quality.Our works on ecotoxicity indicate that the tolerance of Euplotes vannus to ammonia is higher than some metazoa and their juveniles or larva.