STUDIES ON DYNAMICS OF POPULATION AND PRODUCTION OF SPHAERIUM LACUSTRE:IN LAKE DONGHU,WUHAN

Sphaerium lacustre is a fingernail clam,which is a predominant benthic macroinvertebrate in many shallow lakes along the middle and lower basins of the Yangtze River,and there is little published information on this species in China by far.This paper deals with the population dynamics and production of S.lacustre,a subtropical,shallow,eutrophic lake located near the middle reaches of the Yangtze River.S.lacuster was samples monthly at the eleven stations in Lake Donghu from June 1998 to May 1999.The results showed that the annual average density and biomass were 100.2 ind./m2和12.1g/m2,respectively,and the density and biomass peaks were observed in April(297 ind./m2)and in March(43.8g/m2),respectively.Sphaerium lacustre population was composed of three year classes,among which the 1999 year class was dominant.The annual production of the animal calculated by instantaneous growth rate method and the size-frequency method was:wet weight,42.79g/m2;dry weight(unshelled),2.44g/m2,and corresponding annual P/B ratio was 3.55.The production and P/B ratio of S.lacustre in the present paper were close to the medians of the values reported.The dynamic of mean daily production of S.lacustre was also studied,and it shows that the accumulation of production of S.lacuster mainly occurred in Spring and Autumn.