TEMPORAL AND SPATIAL DISTRIBUTIONAL PATTERNS OF MOLLUSCA IN A TYPICAL AQUACULTURAL LAKE -- DATONG LAKE

The environmental characteristics and Mollusca community in Datong Lake were investigated seasonally from December 2008 to October 2009. Potential effects of intensive aquaculture on water quality and Mollusca in Datong Lake were studied by comparing the current sampling with the historical data in 1960, to provide theoretical support for sustainable fishery of the freshwater lakes. The results showed that Datong Lake was eutrophic and the water was alkaline (8.62 0.07), with higher reducibility (-88.40 9.10 mv). Fifteen Mollusca species were recorded, belonging to 5 families. Bellamya purificata, Corbicula fluminea and Unio douglasiae were the dominant species. Both the mean density and biomass of Mollusca showed significant seasonal and temporal variations. These two parameters in-creased gradually as the sequence of Spring, Summer, Autumn and Winter. In a spatial scale, they showed a pattern of decreasing from Northeast to Southwest. CCA analysis showed that the relationship between Oxidation-reduction po-tential (ORP), pH, dissolved oxygen (DO), depth, electrical conductivity (EC) and temperature (T) and the community variance was more significant. Compared with 1960, the water quality of Datong Lake changed dramatically. The water alkalinity became much higher (7.0-7.5 vs 8.4-8.6); EC was 9 times than before (0.25-0.27 vs 2.17-2.56 mS/cm), and water type changed to reducibility from oxidizability. For Mollusca, Gyraulus albus, Segmentina nitida and Radix which preferred habitat of aquatic macrophytes, and Stenothyra divalis, Limnoperna lacustris and Solenaia oleivara which preferred lotic habitat disappeared. The dominant species of Mollusca have been changed from Lamellibranchia to Gastropoda. The results indicated that habitat destruction and overexploitation were the main factors affecting the Mollusca community in Datong Lake, and they are also the key problems for sustainable fishery in the future.