Diversity and seasonal dynamics of rotifer in Dianshan Lake

The dynamics of rotifer community structure in Dianshan Lake,Shanghai,was studied from 2004 to 2006.Species composition,temporal and spatial distribution,biodiversity index of Rotifer and the relationship between rotifer density and water temperature,Chl.a were analyzed.A total of 53 species were identified,with Polyarthra trigla,Brachionus angularis,Brachionus calyciflorus,Keratella cochlearis,Keratella valga,Filinia longiseta and Epiphanes senta being dominant species.The total density of dominant species accounted for 82.2%,82.7% and 78.8% of the total rotifer density of the corresponding year.The mean rotifer density and biomass,averaged over 2004-2006 were 2 514 ind·L-1 and 2.94 mg·L-1,respectively.The highest density of 11 700 ind·L-1 appeared in St6,March,2005.Seasonal distribution of rotifer density and biomass were consistent among the studied years,that is,spring(4 862 ind·L-1 and 5.45 mg·L-1) autumn(2 300 ind·L-1 and 3.45 mg·L-1)summer(1 773 ind·L-1 and 1.88 mg·L-1) winter(940 ind·L-1 and 0.45 mg·L-1).Spatial distribution of the rotifer density and biomass tends to be higher in the Lake centre site than that at inflow or outflow sites,and lowest at St3 close to the cage culture area.The mean Shannon-Wiener diversity index(H),averaged over year,and among sampling sites was 2.27(ranged 2.08 to 2.50).The rotifer density was positively correlated with Chl.a concentration and the regressive equation is: Rotifer density(ind·L-1)= 521.6 + 64.11 chl.a(μg·L-1)(r=0.634,P0.001).