Vízügyi Közlemények, 2002 (84. évfolyam)

4. füzet - Gulyás Pál: A rotatoria és crustacea plankton minőségi és mennyiségi vizsgálata a Dunán

618 Gulyás PáI Rotatoria and Crustacea, Cladocera, and Copepoda were determined from the filtrate of these samples. The composition and density of the species were determined for each station and the water quality of the river and the mouth stations of their tributaries was determined on the basis of these data The results were compared to those of earlier investigations. A list of taxa were defined on the basis of the count of individuals in a unit volume of water for each station. The mean values of the individuum-counts were defined on the basis of the following scaling: found at a single site: +; in 2-20% of the samples: 1; in 21—40% of the samples: 2; in 41-60% of the samples: 3; in 61-80% of the samples: 4; an in 81-100% of the samples: 5. Next a synthetic species list was generated for the identified water bodies, giving the percentage presence of the specie on the basis of the average counts. The frequency of occurrence was also evaluated in these species lists in the following way: — Rare (+) = in a single sample or in 2—20% of the samples — Frequent (++) = in 21-40% of the samples — Dominant (+++) = in 41-100% of the samples. Results of the investigations are given in Table I. In the Danube reach between Neu-Ulm and Tulcea and in the respective tributaries the following numbers of species were identified: 79 Rotatoria, 27 Cladocera and 14 Copepoda, 120 species all together. Most of the species were of the planktonic type, but tychoplanktonic elements were also found in considerable number. The latter could enter the plankton via the scouring of the bottom deposit, or from among the water plants or from the tributaries. The number of taxa identified in individual sites varied in the following ranges: 4—26 in the Danube, 6-30 in the tributaries. The increase of the number of species and individuals can be observed along the longitudinal profile of the Danube towards the downstream. The occurrence of real potamoplankton communities can be observed from the Hungarian reach and downstream-ward. This is indicated by the presence and frequency of occurrence of the dominant species in the river reach between river kilometres 1806 and 0.00. This river reach was characterised by the dominance of the following species: Brachionus angularis angularis, В. budapestinensis budapestinensis, В. calyciflorus, Keratella cochlearis cochlearis, К. c. var. tecta, Polyarthra vulgaris, Bosmina (Bosmina) longirostris, Acanthocyclops robustus, Thermocyclops crassus. The above listed species are dominant ones in nutrient rich eutrophic and politrophic waters, forming communities of high population density. The list of species was the same as that of the earlier investigations. In certain river sections several other taxons were also identified as dominant ones. Some rare species were also found, such as: Brachionus falcatus, Collotheca atrochoides, Cupelopagis vora.x, Lecane brachydactyla, L. (Monostyla) psammophila, L. (Monostyla) scutata, Monommata longiseta, Trichotria curta (Rotatoria), Alona guttata, A. karelica, Graptoleberis testudinaria (Cladocera). The individual count of the communities varied also within wide ranges. Between 280 and 1,383,600 in the Danube and in 1,140-799,640 in the tributaries (jFigure 3.). The occurrence of several rare species were identified in the German, Austrian and Hungarian Danube reaches: Brachionus falcatus, Collotheca atrochoides, Cupelopagis vorax, Lecane brachydactyla, L. (Monostyla) psammophila, L. (Monostyla) scutata, Monommata longiseta, Trichotria curta (Rotatoria). Alona guttata, A. karelica, Graptoleberis testudinaria (Cladocera). The most species-rich communities were found in the Hungarian and Yugoslav reaches. In the reservoirs of the Danube neither the number of species not the individual count was increased considerably. The individual counts were the lowest in the Austrian, Romanian and Bulgarian Danube reaches. The communities of the highest count were found downstream of Budapest, at Novi-Sad in Yugoslavia and along the Danube reach between the confluences of the rivers Tisza