Typology of a Great River Using Fish Assemblages: Implications for the Bioassessment of the Danube River

Abstract

Matching habitat typology and ecological assemblages can be useful in environmental management. We examined whether a priori defined riverine sections correspond with distinct fish assemblage types along the >2000 km long course of the Danube River, Europe.We also tested whether different sampling methods (i.e. day and night inshore electric fishing and offshore benthic trawling) provide consistent typological results. Analysis of assemblage similarities, indicator species analysis, non-metric multidimensional scaling (NMDS) and kmeans analyses indicated that fish assemblages of the a priori defined Upper-, Middle and Lower-Danubian sections differed slightly, within class variability was high. Although indicator species analysis showed that the Upper-Danube belongs to the barbel (Barbus barbus) zone and the Middle-and Lower Danube belong to the bream (Abramis spp) zone, indicator values of the character species were generally low. The NMDS analyses suggested a weak gradient in assemblage structure along the course of the river with relatively high variability between neighbouring sites. K-means analyses revealed that many sampling sites were in a different class than the a priori defined sections, and classifications at other group numbers did not lead to better classification outcome. Overall, the results do not suggest clearly distinguishable assemblage types with distinct boundaries in the potamal section of a great river. Nevertheless, the division of the potamon to smaller sections may explain some variability in fish assemblage structure, and could be used for bioassessment purposes. The study also shows the importance of multihabitat and multigear surveys in the typological assessment of great rivers.

Habitat mapping of riverine fish by means of hydromorphological tools

“…The results of recent fish surveys were used to determine habitat suitability for the two model species. During these surveys, altogether, 197 sampling units, 500 m long each, were electrofished using an electrified benthic frame trawl at a variety of depth, bed material, and flow conditions along an approximately 350‐km‐long reach of the 417‐km Hungarian Danube River section (for details, see Szalóky, György, Tóth, Sevcsik, Csányi, et al, ; Szalóky, György, Tóth, Sevcsik, Specziár, et al, ; Erős et al, ). In brief, the sampling units were selected along predefined transects to cover representatively the cross sectional (i.e., bank to bank) profile of the main channel.…”

Comparison of littoral and deep water sampling methods for assessing macroinvertebrate assemblages along the longitudinal profile of a very large river (the Danube River, Europe)

“…From source to mouth, the Danube drains 19 countries, which makes the Danube Basin the most international catchment in the world (http://www.icpdr.org/main/danube-basin). The river can be subdivided into three main segments based on its hydromorphological features, namely, the Upper, the Middle, and the Lower Danube (Erős et al, ; Literáthy et al, ; Schiemer, Guti, Keckeis, & Staras, ), although the impressive Danube Delta could be also considered as a separate and unique system. Thus, Lászlóffy (1965) suggested sectioning the Danube River into four sectors—Upper, Middle, Lower, and the Danube Delta.…”

“…However, no comparative study examined to date the differences in inshore and offshore macroinvertebrate assemblages across countries, along the longitudinal profile of the Danube River. Such a study could, among others, help in refining established typological systems, which is often an essential step in bioassessment (Erős et al, ; Hering et al, ). It can also contribute to the increasing knowledge about the organization of inshore and offshore macroinvertebrate assemblages in very large rivers and the effect of sampling on observed community structure.…”

“…On the basis of former studies, we hypothesized the lower spatial variability of deep water samples due to the more homogenous structure of the habitat, at least compared with shoreline assemblages, which usually show a higher species richness and are more variable (Angradi et al, ; Rempel et al, ). We also expected longitudinal changes along the course of the river and especially between the Upper, the Middle, and the Lower Danubian segments, because these differ largely in their hydromorphological characteristics, at least at the segment scale (Erős et al, ; Literáthy, Koller‐Kreimel, & Liška, ; see below). However, the magnitude of differences between littoral and deep water samples relative to longitudinal patterns and the effects of different sampling methods on typological results were largely unknown in this and other large or very large rivers.…”

Scaling fish metacommunities in stream networks: synthesis and future research avenues

“…In addition, the spatial extent of the potamon is much longer than the movement distance of most of its characteristic species, such as those from the genera Barbus and Abramis (Cyprinidae) in Europe. Yet, relatively homogeneous communities can be found for hundreds or even thousands of kilometres in the potamon (McGarvey 2011, Erős et al 2016b). …”