Investigation with Computer ICL System 4 on the morphometry and composition of the population of Dreissena shells from the upper sediment layer of Lake Balaton

Ponyi, Jenő and Tusnádi, Győző and Vanger, Éva and Richnovszky, Andor (1974) Investigation with Computer ICL System 4 on the morphometry and composition of the population of Dreissena shells from the upper sediment layer of Lake Balaton. A Magyar Tudományos Akadémia Tihanyi Biológiai Kutatóintézetének évkönyve, 41. pp. 217-234. ISSN 0365-3005

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Abstract

The authors divided into three age-groups (old, middle-aged, young) the 26 600 Dreissena polymorpha shells found in the upper sediment layer of five transversal sections of Lake Balaton. The age of shells comprises a period of 33-34 years from their settling in the sediment to the investigations. They investigated the volume of shells from different parts of the lake with an ICL System 4 computer, on the basis of 15 statistically comparable samples they established the following: 1. On the basis of hystogram program the morphometries of shells from the different collecting sites and belonging to different age-groups are more or less identical. The size of old and young shells was nearly the same, but the middle-aged ones significantly differed from both. 2. The results of the analysis of variance showed that the variability of samples is different both in the longitudinal axis of the lake and in the three age-groups. Averaging the observed frequencies of the three age-groups and plotting their cumulative curve it is apparent that the structure of young shell population conspicuously differs from the other two. The mean volume of shells is different in both the longitudinal axis of the lake and the age-groups. From this point of view the old and young age-groups are fairly similar, although, they are separated by a long time. The size of middle-aged shells entirely differs from the other two groups. 3. In each of the three age-groups the density of Dreissena shells was most frequent in the south-western corner of the lake (mmsversal section M). The abundance of middle-aged and young groups was nearly identical in the longitudinal axis of the lake, while that of the old group significantly differed. Denoting the values of abundance in per cent, it is apparent that in one of the water areas of the lake (section K) the density of individuals gradually increased from the “old” age to the “young” one. 4. The authors compared their results obtained from the hystogram program and the analysis of variance by two factors with the biological changes observed in Lake Balaton up to now and with the ecological knowledge on this species. They established that the different structure of population of the three Dreissena age-groups may be connected to the horizontal distribution of the suspended available food in the lake and the increasing eutrophication.

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