Effect Of Lake Eutrophication On Community Structure Of Rotifers And Sexual Reproduction Of Filinia Longiseta

The rotifer community structure and species diversity were surveied in five lakes arranged by the trophic state gradient. All lakes locate in Wuhu region (Yangtze River valley). Otherwise, sexual reproduction of Filinia longiseta in two different trophic state areas of Lake Jinghu was investigated, the main contents and results as below:The trophic states of five lakes including Lake Longwohu, Lake Jinghu, Lake Tingtanghu, Lake Fengminghu and Lake Yinhu were evaluated using comprehensive index of trophic state (TLI_C), and the community structure of rotifers, species diversity index (measured by Shannon-Weinner index, Margalef index, and Simpson index) and their relationships with trophic state were analyzed from July 2005 to June 2006. In the five lakes, 82 species of rotifers were identified, which belong to 20 families and 34 genera. 35 species were found in Lake Longwohu, 52 species in Lake Jinghu, 50 species in Lake Tingtang, 41 species in Lake Fengminghu, and 31 species in Lake Yinhu. There were significant differences in the number of rotifer species among the five lakes with different trophic states (P<0.01). The number of rotifer species in each of the five lakes except for Lake Longwohu was negatively correlated with the TLI_C (r=-0.984,P<0.05). Eutrophication increased the total density of rotifers and dominance of the first dominant species but decreased the community evenness and the species diversity index. The decreased species diversity caused by eutrophication was attributed to the increased dominance of the first dominant species.The occurrence and extension of sexual reproduction of Filinia longiseta in the two regions of Lake Jinghu, and their relationships with water temperature, Chl-a concentration, Secchi's disc reading, total rotifer density and F. longiseta density were examined from May to November in 2004. Mictic F. longiseta females were not detected until water temperature was up to 22℃, and Secchi's disc reading was up to 95cm at the small region and 100cm at the large region, respectively. The sexual reproduction of F. longiseta occurred when its density was higher than 122ind.L^-1 at the small region and 113ind.L^-1 at the large region, respectively. The density of mictic females was positively related to the F. longiseta density and the total rotifer density (r_1P=0.665,r_1T=0.500;r_2P=0.611,r_2T=0.538,p<0.01), but the relationships between the density of mictic females and water temperature, Chl-a concentration and Secchi's disc reading were not significant. All the stated-above factors had no significant effects on mictic and fertilization rates. The sexual reproduction of F. longiseta occurred in the early phase of the population growth cycle, and the mictic females were produced in the pattern of punctuation and multi cycles. Maximal mictic ratio...