Seasonal variation of biodiversity and assemblage structure in freshwater nematodes

In a three-year field study we determined the seasonal and annual variation of abundance, biomass, species richness, and community structure of freshwater nematodes at a single station in the eutrophic Lake Obersee. The seasonal patterns observed were consistent and varied little between sampling years. Nematode abundance and biomass were highest in summer. Species richness and diversity peaked in winter. With 152 identified species, Obersee is the most species-rich lake ever described. Species number was not constant over years but the main assemblage structure hardly changed. The community was dominated by the same 4 species throughout the study. Colonization was very strong in winter while extinction rates were high in summer. This study shows that the community structure of free-living nematodes depends strongly on the season investigated.