L. Forró szerk.: Miscellanea Zoologica Hungarica 10. 1995 (Budapest, 1995)
Gulyás, P.: Rotatoria and Crustacea plankton of the River Danube between Bratislava and Budapest
species (95), while Copepoda (17 species) and Cladocera (36 species) were represented in smaller numbers. Table 1 shows the yearly changes of species number of different groups. Table 1. Changes in species numbers of different taxonomic groups 1992 1993 1994 Rotatoria 71 62 64 Copepoda 11 14 11 Cladocera 28 25 20 Sum 110 91 95 Occurrence of several rare species was also recorded having importance from faunistical point of view. These are: Brachionus diversicornis honioceros, Dicranophorus prolectes, D. uncinatus, Elosa worallii, Euchlanis triquetra, Lecane stichae, L. stokesii, Lepadella quadricarina, Lindia torulosa, Ptygura melicerta, Eurytemora velox, Alona intermedia, Bosmina coregoni, Daphnia galeata, Monospilus dispar. Species composition of the Rotatoria and Crustacea plankton communities of the Danube is dominated by the presence of Rotatoria species, from which Brachionus angularis, B. calyciflorus, Filinia longiseta, Keratella cochlearis, K. cochlearis tecta, K. quadrata and Polyarthra vulgaris occurred in almost all the samples. Amongst the microcrustaceans near dominant were only the larvae of copepods. With smaller relative frequency but in many places, the following taxa were identified: Asplanchna priodonta, Brachionus budapestinensis, B. leydigi tridentatus, B. quadridentatus, B. urceolaris, Cephalodella gibba, Euchlanis dilatata, Kellikottia longispina, Notholca acuminata, N. squamula, Synchaeta pectinata, Testudinella patina, Acanthocyclops robustus f. limnetica, A. vernalis, Mesocyclops leuckarti, Thermocyclops oithonoides, Alona rectangula, Bosmina longirostris, Chydorus sphaericus, Daphnia longispina, Diaphanosoma brachyurum, Disparalona rostrata. These species form the characteristic plankton of slow flowing or near-stagnant eutrophic waters, occurring occasionally in large numbers. Zooplankton communities of the Danube between Bratislava and Budapest can be characterized and described by the dominant and frequently occurring Rotatoria and Crustacea species: Brachionus angularis - B. calyciflorus - Filinia longiseta - Keratella cochlearis - K. cochlearis tecta - Polyarthra vulgaris - Acanthocyclops robustus f. limnetica - Bosmina longirostris. Smallest species number was found at the Bratislava cross-section (1869.0 rkm) during the investigated 3 years, species number varied between 42-46. Also, species diversity of the community was the lowest at this particular sampling site. Species composition is characterized by Rotatoria dominance, the crustaceans were represented in smaller numbers (3-10). Amongst the rare species Dipleuchlanis propatula, Lecane flexilis, L. stichae, L. stokesi, Notholca labis, Eurytemora velox, Bosmina coregoni and Monospilus dispar were recorded. Investigations revealed the occurrence of dominant species characteristic to the other sections of the River Danube. The fast flowing character of the river is unfavorable for the establishment of a species rich Zooplankton community. Near to Rajka, samples were taken from the right side (1848.4 rkm) and at Hrusov left side (1864.0 rkm). No significant differences could be found neither in the number of the taxa present nor in the species composition between the two banks. Taxon numbers of Rotatoria and Crustacea plankton communities varied between 39-61 in the investigated time period. Species number of Zooplankton sharply decreased after the river was diverted in Slovakia in
