L. Forró szerk.: Miscellanea Zoologica Hungarica 9. 1994 (Budapest, 1994)
Csányi, B.: The macrozoobenthon community of the Danube between Rajka and Budapest
Results Results of the faunal survey The total number of benthic taxa in the kick samples was relatively high everywhere (Fig. 2), but it increased to its maximum in the section just upstream of Budapest (36 taxa just at the Surface Drinking Water Works). The cummulated taxon list contains 48 benthic taxa collected by kick sampling from the littoral zone of the Danube (Table 1). Altogether 2 flatworm, 21 mollusc, 7 annelid, 5 crustacean and 14 insect taxa were found in the shallow, permanently inundated region of the river. Almost half of the taxa (22) were found at 5 or more sampling sites during the research period, indicating the relatively high number of common taxa. Numerous new faunal data were gained during the last few years, some species were never detected in this river section. The aquatic neritid snail Theodoxus fluviaülis was known only in few locations of the Tisza river sofar. A considerable population was discovered in 1987, living just above Budapest. The species is distributed along the whole Budapest stretch of the river according to the detailed survey carried out in 1990. New localities were revealed in the next years in Gönyü (1991), in Rajka (1992), by dredging in the middle of the river bed. All of these data suggest that considerable isolation exists between the populations within one river system. Similar results concerning other species of the same genus (Th. transversalis in the Tisza river system) were gained during the last few years, but the reason of the disjunct occurences are still unknown. The characteristic Danubian snail, Theodoxus danubialis is found only in the lower half of the sampled river section, although this species is present at many sites in the Mosoni Danube, situated in the Szigetköz flood plain (Nesemann 1992). The data on the occurrence of the Potamopyrgus antipodarum in the Danube are also new. Two thiarid species, Esperiana esperi and Microcolpia acicularis are found only in the lower Sampling sites Fig. 2. Macrozoobenthon taxa along the Danube River (cummulated results of kick samples collected in 1987-1993)
