STUDIES ON THE ZOOBENTHIC COMMUNITIES OF THE WEST LAKE, HANGZHOU

The West Lake in Hangzhou is an eutrophic lake with a surface area of 5.66 km2 and a mean depth of 1.5 m. In October 1982 and January, April and July 1983, benthic macroinvertebrates were collected at 25 sampling stations in the lake. A total of 54 species were identified, including 22 species of Oligochaeta, 18 chironomids, 6 Insecta other than Chironomidae, 5 Gastropoda, 1 Hirudinea, 1 Nematoda and 1 Isopoda. Only 21 species of Zoobenths were found in the lake excluding the santanyinyue area. Of them, 11 were oligochaetes, 6 chironomids, 1 ceratopogonid, and 3 gastropods. The weighted annual mean density and biomass of zoobenthos were 443.9 ind./m2 and 1.473g/m2 respectively. Oligochaetes and chironomids contributed to, respectively, 80.1% and 19.4% of the total density, and 82.9% and 16.6% of the total biomass. Molluscs, found at the edges of the lake only, were nearly absent due to the particularly soft sediment and the lake of aquatic vegetation caused by eutrophication. Both density and biomass of zoobenthos in the three subareas to the west of the Su Causeway were much higher than those in the two subareas to its east. This reflected the differences in environmental conditions between the two regions. The dominant species in the lake were Limnodrilus hoffmeisteri, Branchiura sowerbyi, Aulodrilus pluriseta, Tanypus punctipennis, Proclaims choreus and Chironomus plumosus. I8 -index indicated that the distribution of each of these species was aggregative. In the Santanyinyue area where aquatic macrophytes were abundant, the number of zoobenthic species was 48 and the composition of dominant species was considerably different from that in the other subareas. The seasonal changes in density and biomass of zoobenthos in the lake were analysed. An evaluation was made on the potential fish production that can be supported by zoobenthos.