Correction to: Niche differentiation among invasive Ponto-Caspian Chelicorophium species (Crustacea, Amphipoda, Corophiidae) by food particle size

A calibration mistake caused systematic error in the microscopic measurements; all filter mesh size values should be divided by a factor of 2.56. As our conclusions were based on the inter- and intraspecific variations of the trait, this systematic error does not influence them in any way

Niche differentiation among invasive Ponto-Caspian Chelicorophium species (Crustacea, Amphipoda, Corophiidae) by food particle size

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

Longitudinal distributional patterns of Peracarida (Crustacea, Malacostraca) in the River Danube

The River Danube plays a central role in the spread of Ponto-Caspian species as a part of the so-called southern invasion corridor (Danube-Main-Rhine system); therefore, changes in its peracarid fauna (comprising the bulk of invasives) merit special attention. The latest international research expedition (Joint Danube Survey 3, 2013) offered an opportunity for updating and synthesizing our knowledge about this group along the Danube, previously based on studies covering only certain river sections and/or dealing with a subset of species. Altogether 17 amphipod, 7 mysid, 3 isopod, and one cumacean species were recorded at 55 sites investigated between Ulm (river km 2581) and the Delta. Recent large-distance expansion of additional Ponto-Caspian species was not observed, but three species (Chelicorophium robustum, C. sowinskyi, and Echinogammarus trichiatus) have been able to shorten their distributional gap in the Middle Danube, E. trichiatus being recorded for the first time in Serbia. Ponto-Caspian peracarids are still gradually advancing in the German section, as well, implying retreat of native Gammarus spp., and impeding the spread of non-Ponto-Caspian invaders. On the contrary, some Ponto-Caspian species seem to have declined in certain river sections; Dikerogammarus bispinosus was entirely missing in the Lower Danube, and several species characteristic of the lower reaches had been recorded previously much farther upstream (most notably Chelicorophium maeoticum and Obesogammarus crassus). The analysis of current and historical distributional patterns revealed that the crucial step in the large-scale spread of Ponto-Caspian species is crossing the section between Baja and the Sava estuary (rkm similar to 1480-1170) - characterized by an unfavorable combination of relatively strong currents and fine bed material - by passive transport. Presence immediately downstream of this section does not appear to promote further expansion in most of the cases; the source region of large-distance dispersal is most likely the Delta, implying that potential future invaders cannot be identified based on their previous expansion in the lower reaches of the river