L. Forró szerk.: Miscellanea Zoologica Hungarica 13. 2000 (Budapest, 2000)
Spolwind, R., Schludermann, C. , Schuster, A.; Waidbacher, H.: Comparison of fish and amphibian communities in a floodplain system of the rivers Traisen and Danube westwards of Vienna
Distance was applied. In our case cluster analysis after Ward provides homogenous cluster results (Bortz 1993, Brosius 1995, Ward 1963), and this statistical procedure was used in similar studies (Pintar & Spolwind 1998, Kummer et al. 1999). Results of the cluster analysis are presented as tables, segregation into clusters and subclusters was performed by interpretation of dendrogams not shown in this paper. Results The comparison of the two alluvial systems reveals that the Danube-Traisen and the Traisen region differ in various parameters. The Traisen region is defined by its larger extent, and due to massive human impacts (settlements, critical groundwater situation) the total number of backwaters, the detected spawning places of amphibians as well as suitable habitats of fish are lower, than in the compared Traisen-Danube area. Table 1. Characterising area - Parameters for the 2 floodplain systems, the Traisen and the Traisen-Danube area. The ecologically usable area is defined as total area minus settlement used area. Parameter Traisen system Danube-Traisen system Total area (m 2 ) 11.546.825 6.184.253 Traisen River length within the system (km) 30.6 8.1 Ecologically usable area (m 2 ) 2.180.512 6.032.512 Total number of backwaters 41 44 Number of Amphibian spawning habitats 26 34 Number of relevant fish habitats 15 20 Number of fish habitats with stable coenoseses 5 10 We defined the "ecologically suitable area" as the total area of a subsystem minus areas influenced by massive human impact (settlements, roads). Although the Traisen subsystem has a much larger total area, the amount of the ecologically usable surface is significantly smaller, than in the compared Danube-Traisen Subsystem. Figure 2 shows differences in size-distribution of backwater habitats in the two distinguished subsystems. Habitats with an extent larger than 5000 m 2 are mainly restricted to the Danube-Traisen area. Small, mainly shadowed, filled in backwaters are dominant in both subsystems. The occurrence of larger habitats in the Danube-Traisen region is reflected by biocoenotic parameters indicating stable fish habitats. Recorded fish and amphibian species During our field investigations we found 30 fish species in the backwater systems, of these only a small portion can form vital populations. We found 13 amphibian species in the entire system, Rana lessonae and Rana esculenta were combined as Greenfrog-complex. The following figure shows the distribution of the detected fish species in the two different sampling areas of the region. The Danube-Traisen area with its heterogeneous backwater characteristics shows higher species numbers and abundances. Most records of rheophilic species can be explained through drift during flood events during summer 1997; only few of the studied running water habitats provide suitable environments for rheophilic species.
