Community Structure And Secondary Production Of Benthic Macrozoobenthos In A Second Order River Of Qingjiang River Basin

The community structure and secondary production of the benthic macro zoobenthos in a second order river-Hujiaxi Stream of Qingjiang River Basin was investigated from April 2006 to March 2007. Major work dealt with exploitation of species composition and functional feeding group of the macrozoobenthos community, the biodiversity of the macrozoobenthos, evaluation of the water quality with the biological index, analysis of the macrozoobenthos life histories, measurement of annual variations of standing stocks of the dominant species, calculation of secondary production of the major taxa. The main results were as follows:1) Altogether 88 species of benthic macrozoobenthos ,from 6 stations, were sampled collected in Hujiaxi Stream, including 3 species of annelida, 3 species of mollusca, 77 species of insecta, 5 species of malacostraca. The spatial and temporal dynamics of the macrozoobenthos community showed that the species number reached its peak in June, and the species number descended to the lowest in December. For microhatitats, the species number in Station 5 (S5) was the largest, and that in Station 1(S1) was the least.2) Functional feeding groups were 7 species of shredders, 52 species of collectors, 7 species of scrapers and 22 species of predators.3) Biodiversities of the benthic macroinvertebrates were calculated. The annual dynamics of Simpson indices fluctuated intensely in S1 (ranging 2.57 to 11.05), while kept much stable in S5 (ranging 4.26 to 7.52). Both Margalef indices and Shannon-Wiener indices varied slightly.4) The community structures in various microhabitats were compared one another, and the Sφrensen indices of the microhabitats were calculated. Generally, the common species were the dominant ones in various microhabitats. More than 75% of the collected species could inhabit at six different microhabitats.The similarity of S4 and S5 was 0.85, that of S3 and S6 was 0.84, and that between S4 and S6 was 0.82.5) Annual variations of standing stocks of dominant species and the community were measured. The annual mean density (ind/m2) and biomass (g/m2 wet wt) of Choroterpes sp., Electrogena sp., Indobaetis sp., Caenis sp., Conchapelopia sp., Eukiefferiella potthasti , Hydropsyche sp.1 and Neureclipsis sp., Sinopotamon teritism , Cardina denticulata were 407 /1.00, 150/0.37, 232/0.30, 91/0.17, 105 /0.05,280 /0.33,167 /0.30, 25/0.02, 35/33.35,13 /1.19, respectively. The annual mean density and the biomass of the community were 2190 ind/m2 and 41.77g/m2.6) Bioassessment was conducted using Shannon-Wiener diversity index, FBI index and BI index. The water quality of Hujiaxi Stream was fairly clear, except for S6 where the water quality was slightly polluted due to the drainage of inhabitats and agriculture.7) The life histories of 10 dominant species were analyzed. Choroterpes sp., Electrogena sp., Indobaetis sp. had 3 generations per year, while Caenis sp. Conchapelopia sp., E. potthasti, Hydropsyche sp1., Neureclipsis sp. and C.denticulata were bivoltine. S.teritism developed one generation every four years.8) Secondary production of major groups of macrozoobenthos in Hujiaxi Stream was calculated. Production (g/m2 wet wt) and P/B ratios were:(1) Ephemeroptera: Choroterpes sp. was 441.42/14.31, Electrogena sp. was 434.88 /17.56, Indobaetis sp. was 747.21 /15.03, Caenis sp.was 40.52/7.16.(2) Chironomidae: Conchapelopia sp., 1.24/2.31; E. potthasti,2.80 /5.09.(3) Trichoptera: Hydropsyche sp1., 42.68 /11.44; Neureclipsis sp., 1.74/7.65.(4) Decapoda: S.teritism, 100.58 /0.26; C.denticulata, 67.40 /4.72.9) Patterns of daily production and temporal overlap were computed. All of the proportional similarity indices (PS) between the major groups of macrozoobenthos were more than 0.50.