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During the day, changes in the spatial distributions of organisms in the water column occur repeatedly, especially in diurnal vertical migrations, which affect abiotic and biotic components of ecosystems. The migratory behaviour occurs worldwide in the oceans and in fresh water, in different habitats and under different physical conditions. The main migrants are gelatinous zooplankton, which are a heterogeneous group of invertebrate animals, although phytoplankton, nekton and other representatives of zooplankton also migrate. The main focus of the study of diurnal vertical migrations is proximate and ultimate factors that influence the migration. Furthermore, occurrence and density of organisms are examined. To study vertical migrations of gelatinous zooplankton, it is the easiest to study jellyfish because of their size. The distribution behaviour might also be observed in freshwater zooplankton. Two university studies of diurnal vertical migration of freshwater jellyfish were executed in previous years. This work aims to: summarise the current knowledge about spatial distribution - especially of diurnal vertical migration, describe in detail proximate and ultimate factors and compare them between freshwater jellyfish, gelatinous zooplankton and jellyfish. Key words: gelatinous zooplankton,...

Phosphorus (P) is considered as the most frequently limiting factor for phytoplankton growth in freshwater environments. One of the ways, how to solve the lack of P in algae and cyanobacteria, is the production of extracellular phosphatases. Extracellular phosphatase activity (PA) of phytoplankton at the single cell level was investigated in three acidified mountain lakes - Čertovo, Prášilské and Plešné in the Bohemian Forest (Czech Republic) from May to September 2007. PA of phytoplankton was detected directly at the site of enzyme activity using the fluorescence labelled enzyme activity technique (FLEA) and epifluorescence microscopy. The FLEA technique is based on colourless substrate ELF phosphate (ELFP) that is converted by enzymatic hydrolysis to the insoluble fluorescent product ELF alcohol (ELFA), which marks the site of PA. This thesis is divided into two parts. The first part (in Czech) is aimed at a general comparison of PA of phytoplankton in the three Bohemian Forest lakes. PA was characteristic for dinoflagellates Gymnodinium uberrimum, Gymnodinium sp. and Peridinium umbonatum that were ELFA labelled in all lakes almost during the whole season. Other species (e.g. Carteria sp., Chlorogonium fusiforme or Synura sp.) were active either in only one of lakes or in some samples. PA was...