Functional Changes in Benthic Freshwater Communities after Dreissena polymorpha (Pallas) Invasion and Consequences for Filtration

Abstract

Dreissena is extremely abundant in waters it invades, and dramatically changes benthic invertebrate communities in terms of total biomass, species composition, and the relative abundance of functional groups. We analyzed the relative abundance of feeding functional groups of the benthic community before and after zebra mussel invasion in three Belarussian lakes, four lakes after invasion only, and one lake in the same region that has not been invaded. After invasion, benthic structure was dominated by one trophic group - filterers. This group accounted for greater than 96% of the total biomass of benthic invertebrates. We found that the relative abundance of feeding functional groups in the rest of the benthic community, without including Dreissena biomass, was also different in lakes examined before and after zebra mussel invasion. Before invasion and in the un invaded lake, planktonic invertebrates filtered a volume equivalent to the volume of the lake within few days, and were more than 200 times more effective than benthic filterers, which would take about 4 years to filter an equivalent volume. After Dreissena invaded the lakes, the total average biomass of all benthic invertebrates (including zebra mussels) increased more than 20 times. The filtration efficiency of the benthic community increased greater than 70 times, and the time required to filter the volume of the lake was not significantly different than that for zooplankton. These dramatic changes will alter the relative roles of the plankton and benthos in a variety of ecosystem functions, especially the movement of carbon from the plankton to the benthos.