| Abstract [eng] |
The main objective of this work was to investigate the effect of hydromorphological features of the rivers and invasive species to the molluscs community structure. The selected rivers were: Babrungas, Lakaja, Peršokšna, Verknė and Žeimena. In these rivers mollusc abundance, biomass, biodiversity and dominance were examined. What is more, the laboratory experiment was made to check the influence of infestation of Dreissena polymorpha on Unio pictorum mussel somatic growth. Durind the study, 31 species of freshwater molluscs were found in 5 examined rivers. The bigest species richness was found in a coldwater river Verknė (22 species) and the lowest – in warmwater river Lakaja (7 species). First time in a freshwaters of Lithuania, invasive species Potamopyrgus antipodarum was found in a lake Vilkokšnis and Verknė river. The hypothesis, that dreissena is most abundant near the outfall and decreases in the continuum of the rivers was tested. The most significant effect of Dreissena polymorpha to the mollusc communities was found to be near the outfall of the rivers, where its abundance and biomass are biggest. This effect declines, because zebra mussel abundance and biomass decreases in the continuum of the river. What is more, the effect of hydromorphological features, such as substrate and current speed, of the rivers to mollusc abundance, biomass and biodiversity was studied. Substrate, current speed and river were found to have significant effect to the abundance and biomass of the molluscs. However, the biodiversity of mollusc communities was significantly affected only by substrate. The hypothesis, that infestation of Dreissena polymorpha has no significant effect to Unio pictorum mussel somatic growth was tested. There were no significant differencies of Unio pictorum mussel dry biomass between the experimental groups in the end of experiment. This could be reffered to inadeaquate feeding during the experiment. |
