Studies On The Community Structure And Some Ecological Function Of Macrozoobenthos In Pond

With the rapid development of the pond aquaculture in China, the output in pond has been more than50%of the total aquacultural output. However, the traditional feeding model with high density and high feeding ratio not only aggravate endogenous pollution, but the waste water promote the eutrophication in the water around.Macrozoobenthos is an important component of aquatic ecosystem which has many significant functions. Such as playing a important role in the aquatic substantial circulation, promoting the substantial exchange of the sediment-water interface. Meaningwhile, Macrozoobenthos is not only the natural food of the bottom-living fish, such as the carp (Cyprinus carpio L.), but also the indicator of water pollution.The community structure and some ecological functions of Macrozoobenthos in the ponds of the Chonghu fishery in Gong’an, Hubei are researched in this paper. The results are summarized as follow:1. Investigation on the community structure of Macrozoobenthos in3ponds with Grass carp as major cultured fish, the species are few. In pond1, the dominant specie was Alocina longicornis. But in pond2and pond3, only Olignehaeta and Chironomid larva had been found, the dominant species were Limnodrilus hoffmeisteri、Branchiuro sowerbyi、Microchironomus sp.and Chironomus plumosus. The average standing crop of Alocina longicornis in pond1was153.19kg, which had contained TN、TP6.24kg and0.43kg respectively. In pond2, Chironomid larva and Oligochaeta’s total weight were11.34kg and21.98kg respectively, which had contained TN、TP0.77kg、0.08kg and1.47kg、0.19kg separately. The average standing crop of Chironomid larva and Oligochaeta in pond3were3.97kg and13.01kg,which had contained TN、TP0.27kg、0.03kg and0.87kg、0.11kg respectively. Macrozoobenthos can be ingested by fish and then fished out of the water bodies; aquatic adult insects can fly away from the water, which are effective ways to clean the nitrogen and phosphorus in the pond.2. A total of10species were found in ponds, among which Oligochaeta(5) and Chironomid larva(5), accounted for50%and50%. The community structure of macrozoobenthos in ponds with Grass carp (Group C) and in ponds with Pelteobagrus fulvidraco (Group H) were significantly different(p<0.01). In group C, the average standing crop of Macrozoobenthos were0.52g/m2and86.44ind./m2respectively, the dominant species were Limnodrilus hoffmeisteri、Microchironomus sp. and Propsilocerus akamusi, which accounted for20.46%、19.12%、37.89%. Besides, in group H, the dominant specie was Limnodrilus hoffmeisteri, the average biomass and density were9.30g/m2and1411.96ind./m2, which accounted for59.90%and86.84%.3. Reported the efficiency of water purification in pond by Bellamy a purificata with the different densities. The experiment was carried out by culturing different densities (287.86g/m2、590.28g/m2、1237.03g/m2) of Bellamya purificata in pond water at30.5℃. The result showed that DO contents of differernt groups, which were positively correlated to the densities of Bellamya purificata(R2=0.8568,p<0.05), all decreased in varying degrees with significant differernce from the contrl group(p<0.05). The concentration of pH fluctuated in the range of7.76-9.63and was dramatically lower than that of the control group(p<0.05). Bellamya purificata showed effective removal effect on TN, NH4+-N, SS, Chl-a. Except for NH4+-N, the removal efficiency showed a certain correlation with the stocking densities. Bellamya purificata in different treatment groups removed TN by14.41%,29.43%,32.88%; NH4+-N by15.65%,11.38%, and19.92%, respectively. While the suspended substance and chlorophyll removal rates were40.22%,59.78%,73.91%and1.59%,10.59%,26.60%.4. Macrozoobenthos is very significant in circulation of the sediment-water interface. Bellamya purificata、Branchiuro sowerbyi and Propsilocerus akamusi can release nutrition from the sediment to the water, a positive correlation appeared between the releaser and the biomass. The concentration of NH4+-N and PO43--P changed rapidly, until the forth day, they settled out. The reason may be the strenuous activity of the Macrozoobenthos to adjust to the new environment.