In China, few researches have been carried out on meiofauna of lakes. To understand basic characteristics of meiofauna communities in the Yangtze shallow lakes, an algae lake (Eastern Tangsunhu Lake) and a macrophytic lake (Eastern Xilianghu Lake) were investigated seasonally during 2007-2008. Community characteristics of meiofauna in the Yangtze shallow lakes have been comprehensively described, with a discussion on environmental parameters and density of meiofauna. Also, ecological role of meiofauna in these lakes was discussed. The results are mainly as follows:
1. A brief systematic account of meiofauna was presented. A systematic account of 12 species belonging 9 families and 12 genera were presented. Among which 5 species were from Nematoda, 2 species from Cladocera, 2 species from Ostracoda and 2 species from Copepoda.
2. Community characteristics of meiofauna in the shallow lakes were systematically described. A total of 34 species belonging to 5 orders, 17 families and 30 genera were identified. The species number was 25 in both Eastern Tangsunhu Lake and Eastern Xilianghu Lake. The biodiversity of meiofauna in the Eastern Xilianghu Lake were higher than that in the Eastern Tangsunhu Lake. The density, wet biomass and production of meiofauna in the Eastern Tangsunhu Lake were 139.5×103ind/m2, 2.8g/m2 and 25.1g/(m2.a), respectively. And the density, wet biomass and production of meiofauna in the Eastern Xilianghu Lake were 58.5×103ind/m2, 0.78g/m2 and 7.0g/(m2.a), respectively. No significant seasonal changes of meiofauna density were found in these two lakes. Nematodes were the most predominant group, comprising 44-52% in species number, 53.4-72.5% in density and 35.0-63.8% in wet biomass. The analysis of vertical distribution showed that 68.4-69.5% of the meiofauna were in the top 0-5cm of sediment.
3. Dominant families and functional feeding groups of the Nematoda were analyzed in these lakes. The dominant families of Nematoda were Dorylaimidae, Tobrilidae in the Eastern Tangsunhu Lake and Actinolaimidae, Mylonchulidae, Dorylaimidae, Ironidae, Tobrilidae in the Eastern Xilianghu Lake. Most Nematoda feed on organic matter, other nematodes and algae. Organic matter accounted for a higher proportion of food in the algal lake, and bacteria accounted for a higher proportion of food in the macrophytic lake.
4. Relationship between community characteristics and environmental factors were analyzed. Environmental analyses showed that the density of meiofauna correlated significantly with Secchi depth (r=0.57，p=0.03) and total phosphorus of lake water (r=-0.55，p=0.01) in the Eastern Tangsunhu Lake. This indicates that total phosphorus was the factor influenced community characteristics. However, there is no obvious relationship between density of meiofauna and environmental factors in the Eastern Xilianghu Lake.
5. Ecological role of meiofauna in these lakes was discussed. Meiofauna are not only decomposers but also consumers in food chain. The ratio of wet biomass between meiofauna and macrofauna was 2.3-4.9%, and that of production was 8.7-37.5%. Our result shows that meiofauna plays an important role in the material circulation and energy flow of benthic food webs in the Yangtze shallow lakes.