L. Forró szerk.: Miscellanea Zoologica Hungarica 7. 1992 (Budapest, 1992)
Gulyás, P.; Forró, L.: Composition and abundance of microcrustacean fauna in the Upper Reservoir (Hídvégi-tó) of the Kis-Balaton
MISCELLANEA ZOOLOGICA HUNGARICA Tomus7. 1992. p. 39-51 Composition and abundance of microcrustacean fauna in the Upper Reservoir (Hídvégi-tó) of the Kis-Balaton by P. Gulyás and L. Forró (Received March 11,1992) Abstract: The first stage of the Kis-Balaton Protective System has been operating since 1985. It was constructed with the aim to inhibit or reverse the deterioration of water quality in Lake Balaton. From 1985 through 1989, 32 cladoceran and 13 copepod species were recorded from the various habitats of it (plankton, mud surface, phytal). On the basis of species composition of planktonic crustaceans five water quality regions could be distinguished in this impounded water between 1985 and 1987, while in 1989 only 3. In the samples collected from mud surface by means of funnel traps only few species were found, the copepod species Acanthocyclops robustus £ limnetica being also dominant in the plankton was the most frequent. Along the longitudinal axis of this lake the number of individuals diminished in southern direction. The results showed that the lake is still young, and the assemblages of planktonic and mudliving crustaceans are not constant. Key words: Kis-Balaton Protective System, Cladocera, Copepoda, number of individuals, biomass, water quality region. Introduction Attention was called to the deterioration of water quality in Lake Balaton as early as in the fifties by Sebestyén (1953). Algae appeared in increasingly greater amounts, areas covered with aquatic macrophytes diminished, and planktonic eutrophication intensified. The first spectacular sign of these changes was the algal bloom in the Bay of Keszthely in 1965, which in the subsequent years has frequently recurred. Water quality studies revealed that 35-40% of the plant nutrients in Lake Balaton originates from the catchment area of the River Zala, and enriches the Bay of Keszthely (Joó & Lötz 1980). That is why the water quality has most drastically deteriorated here. To slow down or stop this process, the first stage of the Kis-Balaton Protective System was constructed on the lower section of the River Zala in 1985, and was named lake Hídvégi-tó. This lake has the following dimensions: area = 18 km 2 , volume = 21 million m 3 , average depth = 1.14 m, average retention time = 30 days (Joó et al. 1987). The crustacean fauna has also been systematically investigated here since 1985. The results of this 5-year study are presented in this paper. The results of studies carried out from 1985 to 1990 were summarized by Pomogyi (1991) in a comprehensive work. The most important collisions drawn from the qualitative and quantitative studies on the rotatorian u;;d crustacean plankton in this lake constitute one of the chapters (Gulyás 1991) of this work. The changes and growth of planktonic and benthic biocenoses in relation to water quality are published by Csányi et al. (1989). Other studies on these groups of organisms have not been published so far.
