L. Forró szerk.: Miscellanea Zoologica Hungarica 10. 1995 (Budapest, 1995)
Gulyás, P.: Rotatoria and Crustacea plankton of the River Danube between Bratislava and Budapest
nearly 70 Cladocera and more than, 40 Copepoda species (Bothár & Ponyi 1968, Bothár 1968, 1975, 1985, 1988). In the framework of the International Danube River Expedition in March 1988 the Danube Rotatoria and Crustacea plankton was investigated at 35 sampling points. From these we have investigated 3 sites: 1869, 1819, 1694 rkms. On the basis of this series of investigation Naidenov & Sevcova (1991) identified 59 Rotatoria, 13 Cladocera and 9 Copepoda taxa, while Pujin (1991) indicated the presence of 28 Rotatoria, 3 Cladocera and 5 Copepoda species. According to the latter author the Hungarian Danube section is characterized by the presence of 21 Rotatoria, 2 Cladocera and 3 Copepoda species. For the evaluation of these results, however, one has to consider the very unfavorable early spring conditions for sampling. The investigation of the Zooplankton communities of the Danube between Rajka-Budapest at our Institute has started in 1981. In the first period the primary aim was to establish a baseline data set for preliminary investigation. Later on the scope of the research somewhat changed, to investigate the interaction between the planktonic communities and hydrological conditions and of hydrobiological state (Gulyás, 1990a, b, 1994a, b, c, Forró & Gulyás 1992). Material and methods Within the frame of the investigations of the Hungarian-Slovakian border waterways financed by the Hungarian Ministry of Environment and Regional Policy research has started in 1992 with regards to the species composition and abundance of Rotatoria and Crustacea plankton. The Danube was sampled at 8 locations between Bratislava and Budapest at bi-weekly intervals. Samples were taken from the middle of the river to achieve a characteristic plankton sample. Collection of the samples therefore, was carried out from ships, ferries, from bridges and from different hydraulic constructions. Samples were taken from the surface and filtered through a 60 urn mesh size plankton net. Volume of the filtered water was 50 liters each. The filtrate was conserved on-site by using 40% formaldehyde solution to achieve a final concentration of 4%, occasionally lugol (iodine) solution was also used. For the taxonomic determination of the animals identification keys by Bancsi (1986, 1988), Gulyás (1974), and Dévai (1977) were used. Taxa lists were prepared on the basis of the above cited manuals (see Appendix). Quantitative samples were counted by using Utermöhl plankton counter microscope, with 5 ml counting chambers. Sampling sites were the following: 1. Bratislava, middle of river (Br) 1869,0 rkm 2. Rajka, right side (Rj) 1848,4 rkm 3. Rajka, left side (Hrusov) (Rb) 1864,0 rkm 4. Medve, middle of river (Me) 1805,5 rkm 5. Komárom, middle of river (Ko) 1868,3 rkm 6. Szob, middle of river (Sz) 1708,0 rkm 7. Nagymaros, middle of river (Nm) 1694,6 rkm 8. Budapest, Surface Water Works (Bp) 1659,0 rkm Evaluation of the results Qualitative composition of Rotatoria and Crustacea plankton communities Analysis of the plankton samples revealed the occurrence of altogether 148 Zooplankton taxa. Largest species and individual numbers were almost always connected to the Rotatoria
