Dr. Éva Murai szerk.: Miscellanea Zoologica Hungarica 4. 1987 (Budapest, 1987)

Kiss, I.: Ecological studies on zooplankton species important for fish farms. II. Interspecific relations between zooplankton species

MISCELLANEA ZOOLOGICA HUNGARICA Tomus 4. 1987 p. 93-101 Ecological studies on Zooplankton species important for fish farms. II. Interspecific relations between Zooplankton species By I. KISS (Received May 9, 1985) ABSTRACT. Some cases of competition and prédation were examined in Rotatoria and Cladocera species providing the fish progeny with a basic natural food. In the Rotatoria breeds, Brachionus calyciflorus, which multiplies rapidly, appeared in the beginning, then reproduction of the consuming predator Asplanchna species commenced. It has been established that the Cladocera species are able to crowd out the Rotatoria species from the biocenosis of the progeny breeding ponds. There exists a competition for food between the two Cladocera species too, as a result of the more intensive filtering activity. In the case of Brachionus calyciflorus, in the presence of the predator Asplanchna species spine length increases, which means unambiguous protection for the adult animals, and also for most of the young ones. KEY WORDS: Zooplankton breeds, population dynamics, competition, prédation, cyclomorphosis INTRODUCTION The biological relations in Zooplankton communities can generally be observed in connection with the phenomena of nutrition, respiration, reproduction, defense, vertical and horizontal distribution (SEBESTYÉN, 1959). Since the environmental active components function in a complex way, the communal relations of different characters correlate with one another concurrently. Amongy the biotic relations, food relations can be considered as most important. In the characterization of the feeding of planktonic animals, the size of the food, the relation of the consuming animal and the nourishment in terms of order of magnitude, and research on the ways of ingesting the food particles are significant besides the description of the formal and functional features of the nutritive organs (SEBESTYÉN, 1959). The character of the relations among the species was revealed by research on population dynamics. From the changes in the population dynamics of co-existing species (in presence of certain species the low number of individuals of other species, the sudden disappearance of some species from the water habitat) a conclusion could be drawn as to the existent phenomena of competition and prédation. Several experiments prove that Zooplankton species requiring similar environmental conditions and food partition the regions of the water habitat among themselves, thus showing definite vertical and horizontal distribution (MAKAREWICZ and LIKENS, 1975; LANE, 1978, HALBACH, 1979). Certain planktonic organisms form communities of seasonally varying composition of species as a result of the difference of their ecological requirements. Thus, e. g. in the case of most Cladocera spp., it can be proved that they are not concurrently present in a water habitat (LYNCH, 1978). Besides prédation, the decrease in the number of individuals of certain populations can also be caused by competition. The clarification of the causal relations is rendered more difficult by the fact that a species normally practising filtering activity can appear as a facultative predator species. This is true for most Copepoda spp. (PUJIN, 1971).