DIVERSITY AND DISTRIBUTION PATTERN OF FRESHWATER MOLLUSCS IN THE YANGTZE RIVER BASIN

Based on published studies and some unpublished data of our survey, we analyzed diversity and distribution pattern of freshwater molluscs in the Yangtze River basin. Altogether, 297 valid species are recognized, belonging to 62 genera in 17 families; particularly197 species are endemic to China. Viviparidae, Plenroseridae, Pomatiopsidae, Limnaeidae and Unionidae are the predominant components, accounting for 250 species and 84.2% of the total. Total species richness decreases while the ratio of endemic species richness to total species increases with elevated elevation. Species richness in the tributaries and lakes of the Yangtze River were greatly higher than those in the mainstream, suggesting that the tributaries and lakes were essentially important for sustaining molluscan biodiversity in the basin. Species richness, endemic species and endemisity were significantly variable at the sub-basin scale with the most diverse fauna occurred in the Lake Dongting sub-basin and Lake Poyang sub-bain. Cluster analysis indicated that distribution the patterns of freshwater molluscs reflected the topographic characteristics of the basin, and formed the patten of medium altitude plateau, medium-low altitude hilly area, and low-altitude plain. Species distribution of the major groups extremely varied: 1) the Viviparidae and Limnaeidae had the broadest distribution; 2) most species of the Plenroseridae and Pomatiopsidae had a restricted distribution only at one sub-basin; 3) the species of the Unionidae were concentrated in the mid-lower Yangtze Basin, especially in Lake Poyang and Lake Dongting with 58 species and 45 species respectively. Our study indicated that Lake Dongting, Lake Poyang and the lower Jinshajiang sub-basin (especially lakes in Yunnan-Guizhou Plateau) had most diverse molluscan fauna, and they should be considered as hotspots for conservation of freshwater molluscs.