ON ECOLOGICAL DISTRIBUTIONS AND POPULATION DENSITIES OF MOLLUSCA IN LAKE TUNG-HU,WUCHANG

By analysing the data of mollusca from quantitative samples taken by a 1/7 M2 hand-grab from 101 sampling positions randomly distributed in Lake Tung-hu dur-ing March-April and October-November 1963,preliminary results concerning someecological aspects of Mollusca in this shallow lake were obtained.They may besummarized as follows:(1) The most abundant forms of Mollusca are the gastropods,among which Alocinma longicornis,Parafossarulus striatulus and Bellamya aeruginosa are predo-minant.They represented 79% of total molluscan biomass in spring and 91% inautumn. (2) The population structures of predominant species exhibit a definite patchi-ness.The values of ∑(x-x)2/x(n-1) as computed from the data of three predo-minant gastropods were all significantly greater than unity.(3) The distributions of population densities of predominant species are cor-related with certain environmental factors.It was found that A.longicornis and P.striatulus were more abundant in localities where aquatic vascular plants were presentwhile B.aeruginosa was plenteous upon sandy bottom.The numerical distributionsof P.striatulus and B.aeruginosa were also shown to be correlated with the waterdepth.(4) The standing crop of Mollusca as a whole in the lake during 1963 was 8.7 g.per M2 (ca.243 metric tons in whole lake) in spring and 30.5 g.per M2 (ca.850metric tons in whole lake) in autumn.