Species Diversity Of Freshwater Mussels In Poyang Lake And Five Rivers Of Jiangxi Province And Its Response To Changing Water Level

Poyang Lake Basin is one of the hot-spots of biodiversity inhabiting freshwater mollusks in the middle and lower reaches of the Yangtze River. The freshwater mollusk classification and distribution pattern of this area are short of systematically collation and definitive data. A survey on Poyang Lake and the main stream of the five Rivers (Ganjiang river, Fuhe river, xinjiang river, Xiuhe river and Raohe river) were conducted in 2010-2013, and the taxonomy and ecology of freshwater mollusk were included. In addition to the species recording and description, the diversity pattern, standing crop and their relationships with environment factors in Poyang Lake and the main steams of "Five rivers" were also analyzed. The main results are as follows:1. A total number of 123 species of freshwater mollusks in Poyang Lake and the main streams of five rivers were recorded, of which 58 species of gastropod belonging to 21 genera and 12 families, and 65 species of bivalve belonging to 16 genera and 3 families, including 4 newly recorded species:Lepidodesma aligera (Heude), Solenaia triangularis (Heude), Solenaia rivularis (Heude) and Rivnlaria globosa (Heude). Further descriptions on the new record of snail Ferrissia parallela (Haldeman) and mussel Pilsbryoconcha compressa (von Martens) from China were given. The morphology of a kind of non-parasitic metamorphic glochidia was observed using light microscopy and scanning electron microscopy.2. At the view of distribution pattern, there were 109 mollusks distributed in Poyang Lake, while in the main stream of Ganjiang, Fuhe, Xiuhe, Xinjiang and Raohe Rivers, the numbers of the species were 64,22,47,37 and 32 respectively. Poyang lake basin is extremely rich in freshwater mollusks, it accounted for 40.73% of overall freshwater mollusk species in the Yangtze River basin, and 78 Chinese endemic species, of which 29 gastropods and 49 bivalves in Poyang Lake and the main stream of five rivers. Faunal similarity analysis showed that the freshwater mollusk distribution in Poyang Lake and main streams of the five rivers could be divided into three branches:branch Xiuhe, Raohe and Ganjiang River; branch Fuhe and Xinjiang River; and branch Poyang Lake. From the perspective of the mollusk distribution pattern in the main streams of five rivers, the results showed that mussel species diversity significantly increased along longitudinal gradient of the river in the middle and lower reaches of the main streams, while in Poyang Lake, mussel distributed intensively in the estuary delta and in southern area of Poyang Lake.3. The survey results of freshwater mollusk standing crop in Poyang Lake showed that the average density and biomass of snail were 51.271±160.545 ind/m2 and 33.743±102.609 g/m2 respectively. In terms of the unionid, both the density and biomass were the highest in north Poyang Lake, followed by middle Poyang Lake, and minimum in south Poyang Lake. The density and biomass of Corbicula fluminea were 4.484±6.870 ind/m2 and 11.465±15.141 g/m2 respectively.The standing crop of freshwater mollusks in main streams of five rivers was significantly less than the lake. The mean density and biomass of freshwater mollusks in Five Rivers were as follows:Ganjiang River 28.912±37.332 ind/m2,78.695 ± 99.250g/m2; Fuhe River 2.598±6.242 ind/m2,8.810± 16.229 g/m2; Xiuhe River 13.237±21.944 ind/m2,42.544 ±59.709 g/m2; Xinjiang River 34.252±30.869 ind/m2, 72.309± 67.645 g/m2; and Raohe River 40.325±38.740 ind/m2,94.697± 86.151 g/m2.4. A lot of complex factors influences the standing crop of freshwater mollusks. The impact of sediment, water depth, flow velocity and the transparency on mussel density and biomass in Poyang Lake were analyzed. The results showed that the standing crop was quite high in the mud and silt sediment. The standing crop was also high when the water depth was below 4 meters, while it was significantly decreasing in the water depth 5～6 m. The velocity below 0.5 m/s did have much effect on the standing crop. As for the transparency, the standing crop was relatively high when it was 0.25～0.75 m.Four types of habitats were sorted out and surveyed in downstream of Ganjiang River. Two types habitats were found to be suitable for the mussels, in which the species number were 37 and 33 respectively, accounting for 69% of the total number of survey habitats. Most of mussel beds were observed to be revealed when the water level at 8～9 m in the Ganjiang river downstream. The distribution pattern of the mussel bed was also considered to be the long-term adaptation of mussels to changeing water level, and it implies the significance for the mussel conservation that the water level of Ganjiang river downstream should maintained above 9 m in the dry season.