To fit or to belong: characterization of the non-native invader Eurytemora carolleeae (Copepoda: Calanoida) in the Oder River system (Central Europe)

The Eurytemora affinis species complex (Copepoda: Calanoida) is widespread in coastal and estuarine waters in the northern hemisphere. The species Eurytemora carolleeae belongs to this complex. It was recently described and recognized as an invasive copepod for European waters. Since then, it was found in a few European estuaries. Based on molecular and morphological studies, we observed that E. carolleeae has expanded into new freshwater habitats in Central Europe. We carried out detailed morphological analysis for this species which indicates the potential higher stability of the populations in freshwater habitats compared to brackish waters. Fluctuating asymmetry did not significantly differ between freshwater and brackish water habitats, but the share of deformed specimens was considerably larger in brackish waters. We also found that season and habitat influenced t he morphology of Eurytemora. In the molecular analyses, we focused on mitochondrial (COI) as well as nuclear gene markers (18S rDNA, ITS1-2) in E. carolleeae. In addition, for the first time, we analyzed the cytochrome b gene of the latter species. A wide distribution of E. carolleeae in the Oder River system in Central Europe indicates that it is a suitable habitat for the present populations and suggests further expansion of the species into continental waters.