L. Forró szerk.: Miscellanea Zoologica Hungarica 10. 1995 (Budapest, 1995)
Gulyás, P.: Rotatoria and Crustacea plankton of the River Danube between Bratislava and Budapest
in all cases Rotatoria, Crustacea were represented generally at lower species number, compared to the two previous upstream sampling sites. New rare species, in addition to the previously listed were: Dicranophorus uncinatus, Keratella cochlearis macracantha, K. cochlearis micracantha and Daphnia galeata. Dominant taxa were identical with the previous sampling sites. On the approximately 35 rkm long river section no water quality changes can be observed on the basis of the species composition of Zooplankton communities. Quantitative composition of Rotatoria and Crustacea plankton communities Abundance of the animals changed between 12-6648/100 liters in the river section of Bratislava-Budapest in the period of 1992-1994 (Figs 1-3). In general, it is concluded that values are showing a constant increase in the downstream direction. The degree of this increase was still slight in 1992, while in 1993 and 1994 this trend was more expressed. In certain seasons the abundance was especially high downstream of Medve, and at Szob and Nagymaros. River section downstream of Medve has lowered water velocities providing better environmental conditions for the formation of communities usually observed at high abundance, with eutrophic water species, such as Brachionus, Filinia, Keratella, Polyarthra, Acanthocyclops, Bosmina, Daphnia, Diaphanosoma, Moina. As it can be seen from the figures and tables, largest values were measured in the above named sampling points in May and September of 1992, and also in May and June of 1993. Individual abundance of the animals were noticeably less in 1994, than in the two previous years. These phenomena - longitudinal increase of individual abundance values, and large individual number of a few species - indicate an increasing eutrophication process in the River Danube. Fig. 1. Longitudinal changes of the Rotatoria and Crustacea fauna of the River Danube in 1992
