POPULATION DYNAMICS, ANNUAL PRODUCTION AND TROPHIC BASIS ANALYSIS OF THE DOMINANT SPECIES NEOCARDINA DENTICULATA SINENSIS (KEMP) IN HUJIAXI STREAM

Macrozoobenthos community plays an important role in material cycle and energy flow in riverine ecosystem. During the period of April 2006 to March 2007, an investigation on population dynamics, annual production, and trophic basis analysis of a dominant macrozoobenthic species Neocardina denticulata sinensis (Kemp) in a second order river (Hujiaxi Stream) of Qingjiang River Basin was conducted. From the upper to the lower reach of Hujiaxi Stream, we chose six types of habitats to collect quantitative samples. Station 1 (S1) was in the middle of a peaceful flowing section with grit bottom, station 2 (S2) was at a branch away with silver sand, station 3 (S3) was under a waterfall of the riffle with large boulders, station 4 (S4) was at the lower reach of a weir with slowly flowing water and cornbrash, station 5(S5) was at a riffle with much litter and many cobbles on the bed, station 6 (S6) was at the lower reach of a sewage outlet with gravel-sand bottom. At each station, samples were taken with a Surber net (60 mesh), and the specimens were kept in 10% formalin for later processing. The life cycle of N. denticulata sinensis was analyzed by the monthly size-class frequency distribution, the annual production were estimated by size-frequency method, the trophic basis analysis followed the method employed by Wallace and Benke (1997). The results showed that N. denticulata sinensis appeared to develop two generations per year. The density of its population reached its peaks in July (31 ind/m2), October (35 ind/m2), December (20 ind/m2) and February (20 ind/m2) of next year. The biomass reached its peaks in April (1.76 g/m2), July (4.74 g/m2) and February (2.38 g/m2) of next year, respectively. The annual production and the annual P/B ratio of N. denticulata sinensis estimated with size-frequency method were 67.40g/m2, 4.72. The proportions of various food types as well as their contribution to production with foregut content analysis were also examined. The results showed that amorphous detritus and animal materials were the most important food types, accounting for 79.9% and 12.5 % of foregut content, and contributing 62.50% and 34.18% of the production, respectively.