Spread and distribution pattern of

The exotic Chinese pond mussel (Sinanodonta woodiana) is the biggest bivalve in Europe, it was first reported from Lake Balaton in 2006. In 2011 summer relative abundance and biomass of S. woodiana and native unionids were recorded at 21 sampling sites, in order to analyse the speed of dispersion of the Chinese pond mussel and to reveal its possible ecological impacts on native unionids. GPS coordinates of the sampling sites were recorded, spatial distribution of the data shows that high abundances and biomass are characteristic along the northern shore of the lake. In the western part of the lake, in the Keszthely Basin, its biomass may amount to as much as 50–80% of the total unionid biomass. In this basin, comparing these data to the distribution of unionids measured in 1992/93, the impact of S. woodiana seems high, as A. cygnea has been replaced by S. woodiana and the ratio of A. anatina reduced from 17.8% to 8.6%. Taking into consideration that S. woodiana has so rapidly developed high relative abundance and biomass close to the supposed source of introduction and it has a high spread potential in the lake, future increase in population size (and dominance) can be expected.