LAUSR

After Chelicorophium curvispinum, two other Ponto-Caspian tube-dwelling, filter-feeding amphipod species (Chelicorophium robustum and Chelicorophium sowinskyi) have colonized several catchments in Central and Western Europe in recent decades. To reveal the mechanism of niche differentiation among them, we measured the mesh sizes of their filtering apparatus and analyzed multi-habitat sampling data from the River Danube using RDA-based variance partitioning between environmental and spatial explanatory variables. Morphometric data showed a clear differentiation among the species by filter mesh size (C. curvispinum > C. robustum > C. sowinskyi). Field data also indicated the relevance of suspended matter; however, the mere quantity of suspended solids included in the analysis could not explain the abundance patterns effectively. Current velocity, substrate types, and total nitrogen content also had a non-negligible effect; however, their role in the niche differentiation of the species is not evident. In summary, differences in their filter mesh sizes indicate a niche differentiation by food particle size among the invasive Chelicorophium species, allowing their stable coexistence given sufficient size variability in their food source. Consequently, the two recent invaders increase the effectiveness of resource utilization, resulting in a more intensive benthic–pelagic coupling in the colonized ecosystems.