Zoological investigations in the open water Potamogeton perfoliatus stands of Lake Balaton

Biró, Kálmán and Gulyás, Pál (1974) Zoological investigations in the open water Potamogeton perfoliatus stands of Lake Balaton. A Magyar Tudományos Akadémia Tihanyi Biológiai Kutatóintézetének évkönyve, 41. pp. 181-203. ISSN 0365-3005

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Abstract

With a well-closing reed-grass collecting net (Fig. 2) we collected the fauna of Potamogeton perfoliatus at seven points of Lake Balaton (Fig. 1) in 1970-72. The most frequent species in these submerged vegetations were Sida crystallina, Corophium curvispinum, Eudiaptomus gracilis and Mesocyclops leuckarti. Apart from the frequently collected Chironomida larvae, the rarer Dicerogammarus villosus, Limnomysis benedeni and Trichoptera larvae may also be regarded as constant inhabitants of the reed-grass stands (Table 1). More than half of the species are metaphytic (Table 2). There is also a difference between the submerged vegetations in the different areas of Lake Balaton. The formation of the openwater fauna at the two ends of the lake is different from that found a t the other collecting sites. In the reed-grass vegetation, in front of the mouth of river Zala, at the beginning and middle of summer the Chironomida larvae and cladocerans (Sida crystallina, Chydorus sphaericus), while at the end of the season the copepods (Eudiaptomus gracilis, Eucyclops serrulatus, Mesocyclops leuckarti, Acanthocyclops vernalis) were dominant. Also in the Bay of Fűzfő, at the beginning of summer, the Chironomida larvae and Sida crystallina were predominant. Sometimes the number of Eudiaptomus gracilis and Mesocyclops leuckarti was also high. At the end of the season, however, in addition to the copepods the Corophium curvispinum and Chironomida larvae were the most frequent. For the other vegetations of the lake Sida cyrstallina might also be regarded as the most common species at the beginning of summer, but it was replaced by Corophium curvispinum and some copepods (Eudiaptomus gracilis, Eucyclops serrulatus, Mesocyclops leuckarti). In the last 30 years, the fauna in P. perfoliatus has undergone a change. We were not able to collect Asellus aquaticus, but some cladocerans and copepods, formerly unknown in the fauna of the lake, were found. Anchistropus emarginatus new to the fauna of Lake Balaton was collected (Fig. 3). Since Entz’s investigations (1947) and those of Ponyi (1956), Sida crystallina and Corophium curvispinum have been dominant species in the P. perfoliatus stands of Lake Balaton. The quantity of fauna ranged from 1.055 to 11.798 i/100 ml P. perfoliatus. At the mouth of river Zala, in the Keszthely Bay, the number of animals was 2.500 i/100 ml P. perfoliatus in 1970, while in 1971-72 it was 7.700 i/100 ml P. perfoliatus. From Szigliget to Fűzfő this average was 3.300 i/100 ml P. perfoliatus during the three years. The biomass value of the fauna, determined with measuring the volume, ranged from 0.4 to 3.3 g/100 ml P. perfoliatus. In the Keszthely Bay the average value was 2.0 g/100 ml P . perfoliatus, while in the other regions, it was 1.5 g/100 ml P . perfoliatus during the three-year period. The quantity of the biomass mostly depended on the on the number of Corophium curvispinum (Table 1, and Figs. 4, 5, 6).

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