The density and biomass of Dreissena polymorpha living on submerged macrophytes in Lake Balaton (Hungary)

Abstract

Dreissena polymorpha appeared and spread throughout Lake Balaton in the 1930 s. We studied the density, the body length-body mass relationships and the biomass of D. polymorpha living on the submerged macrophytes in the littoral zone at four sites of different trophic status from May to October 2000. The dominant submerged macrophyte was Potamogeton perfoliatus in May/June and July and Myriophyllum spicatum in October, the fresh biomass of submerged macrophytes ranged between 450.64 and 3,171.51 g/m 2 , dry biomass ranged between 61.54 and 381.31 g/m 2 . D. polymorpha represented 2.48-84.85 % of all animals on submerged macrophytes. The density of zebra mussels ranged between 421 and 749,032 ind./m 2 , between 1 and 282 ind./g macrophyte fresh mass, and between 9 and 2,032ind./g macrophyte dry mass. The body length-body mass relationships could be described by simple power function equations for fresh body mass with and without shell and dry body mass with and without shell. Zebra mussel biomass in Lake Balaton varied widely between 0.35 and 1,106.55 g fresh mass with shell/m 2 , between 0.01 and 50.96 g dry mass with shell/ m 2 , between 0.09 and 260.39 g fresh mass without shell/m 2 and between 0.002 and 6.49 g dry mass without shell/m 2 . The estimated respiratory organic carbon loss of total D. polymorpha population in the zone of submerged macrophytes ranged between 0.15 and 338.27 mg C/m 2 day, which is 0.04-154 % of planktonic primary production in different parts of the lake, illustrating the important role of this Ponto-Caspian invasive mussel in the matter-energy flux in Lake Balaton. The density of the zebra mussel (ind./m 2 ) significantly depends on the type of submerged macrophytes and on the water depth. The type of submerged macrophytes and water depth have significant additive and interactive effects on the length of animals. Only the water depth determined significantly the biomass of zebra mussel.