Assessment of the vulnerability of Lithuanian lakes to expansion of Gonyostomum semen (Raphidophyceae)

Invasions in aquatic ecosystems can have negative ecological and economic effects. It is important to identify the impacts of non-native species in order to evaluate the outcomes of invasion processes and implement measures of management. A biopollution assessment method (BPL, or biopollution level index) was applied to measure the impact of Gonyostomum semen (Raphidophyceae) on the lakes of Lithuania. It occurred in humic, lobelia and eutrophic lakes. G. semen , comprising abundance up to 1.05 × 10 6 cells L −1 and biomass up to 24.8 mg L −1 , was assigned as an invasive species that caused recognisable changes on phytoplankton communities, habitats and ecosystem functioning. The dominance of G. semen shifted phytoplankton composition from the prevailing small chrysophytes and green algae to the raphidophyte and large dinophytes being dominant. The assessment for the lakes revealed the highest biopollution level (BPL = 3, strong impact) for the lakes in the northern part, and moderate biopollution (BPL = 2, moderate impact) for the other regions of Lithuania.