Baza pokarmowa zooplanktonu jeziornego

Gliwicz, Zbigniew Maciej

doi:ISSN 0424-7205

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Tytuł: Baza pokarmowa zooplanktonu jeziornego

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There was made a revue of the literature on the problem of significance of phytoplankton, dissolved organic matter, bacteria and organic tripton (detritus and coagulums of dissolved organic matter ) in the feeding of lake zooplankton. Opinions on the subject of possibilities of utilization of dissolved organic matter by plankton animals uderwent numerous changes since the time of Pütter’s theory (1909). In recent years an opinion has prevailed, that the dissolved organic matter can be a considerable source of vitamins and other biologically active substances for zooplankton, but as a basic food material (energetic material) it can be neglected. It does not, certainly, exclude the possibility of utalization of dissolved organic matter in an indirect way, through its coagulums and bacteria developing on it. The basic food source of plankton animals consits thus only of the particulate organic matter, i.e. a matter in the form of particles of the organic fraction of seston (algal cells, bacteria and particles of organic tripton), which can be cought on nets of filtering apparatuses of crustaceans or settled due to sedimentation on the coronae of ciliary trochal discs of rotifers , as a result of water currents caused by these apparatuses. On the basis of scores of the cited papers which discuss the results of alimentary canals analyses of various crustaceans and rotifers species, results of observations on the mechanism of the food intake, results of animals cultures on various kinds of food, and results of experiments on feeding of animals with various species of algae for checking, which of them are grazed the most intensively, it can be stated that the upper size limit of particles available as a food for pelagic species of filtering crustaceans is always lower than a score of microns, and in the case of rotifers even some microns. In connection with the above, large phytoplankton cells and colonies (so called net phytoplankton mainly blue-green algae, diatoms and dinoflagellates) are not available as a food for these species, which are generally a dominant component of lake zooplankton communities. Thus the direct utilization of these big net phytoplankton forms is not significant in the lake pelagial and depends in a great extent on the quantity of certain carnivorous forms in zooplankton communities, which complete the animal food with large quantities of the plant material. These forms can suck (e.g. Leptodora) or even consume whole cells of diatoms or dinoflagellates (e.g. Asplanchna) some hundred microns in diameter. Therefore the plant food directly available for the majority of not predatory zooplankton species is the nannophytoplankton. It results, however, from the comparison of the production value of nannophytoplankton and the food (energy) demand of zooplankton (e.g. Nauwerck 1963), that the production of minute eatable algae does not satisfy the energy demand of zooplankton. The other direct food sources, i.e. bacteria and organic tripton should be then considered. Since the works of Naumann (1918, 1921, 1923) who considered these elements as a main food source, a lot of evidence was collected with the help of laboratory experiments, which show that a lot of common pelagic lake zooplankton species of crustaceans and rotifers can not only consume and assimilate bacteria, but even for many generations they can live without any plant food, even then when the concentration of bacteria does not exceed concentrations met in natural water environments. More controversial is the problem of the significance of the organic tripton (detritus and coagulums of dissolved organic matter) as a food source, as it is considered by many authors as a material of the low value, difficult to assimilate, with the significance rather as a “ballast” material in alimentary canals. ; The significance of bacteria and organic tripton as a food source for zooplanktonbecomes even more important if the fact of often contacts of plankters with the bottom zone of lakes is take n into consideration, as there are quantities of highly calorific organic substances in sediments, and the bacteria concentration is some hundred times higher than in pelagial. These contacts are confirmed by the near bottom maxima of plankton rotifers and crustaceans, which are often observed, especially at the time of Winter stagnation. The field observations on the dynamic of the numbers and production of phytoplankton, bacterioplankton and zooplankton are an additional source of information on the significance of algae, bacteria and tripton in feeding of plankton animals. It results from a revue of papers on this topie that the peaks of numbers and production are observed very often in the following sequence: phytoplankton bacterioplankton zooplankton. It confirms the indirect utilization of primary production by zooplankton through the whole complicated system which can consist of: the dissolved organic matter (often secreated in large quantities to the environment by living algae), bacteria which develop on it, and the organic tripton not living organic matter in the form of particles formed from dead organisms, or due to the physical processes from the dissolved organic matter. Functioning of this system (see also Sorokin 1967, G1iwicz 1969a and Saunders , in press) can have, of course, various relative intensity depending on the type of primary production (more energy reaches zooplankton by this indirect way if the participation of big, uneatable directly phytoplankton forms is bigger), and on the dominant zooplankton species. Dominating macrofiltrators will graze mainly nannoplankton algae of some or even more microns in diameter, the microfiltrators and sedim ntators will graze rather smaller bacteria (G1iwicz 1969b, 1969c).