During gelatinous zooplankton blooms, an enormous quantity of organic matter is released into the environment at once. Dissolved organic matter is exclusively available to marine microorganisms which contribute to its cycling process. Decomposing gelatinous zooplankton represents an excellent substrate for rapid growth of opportunistic, potentially even pathogenic bacterial species, which can drastically influence the structure of marine ecosystems as well as human wellbeing. To predict the response of marine ecosystems on gelatinous blooms, it is important to understand the mechanisms and biochemical processes which regulate the interactions between organic matter of jellyfish origin and metabolic network of the microbial community. The ctenophore Mnemiopsis leidyi is an invasive species, blooming massively in the coastal area of the North Adriatic since 2016. In the thesis, we conducted detailed studies of the microbial decomposition of ctenophores. We studied composition of ctenophore detritus at individual compound level and found out that it contains proteins and lesser amounts of carbohydrates. We were not able to determine lipid content due to its low concentration. We studied the effects of the chemical composition of ctenophore detritus on the microbial metabolic processes. We linked the chemical composition of ctenophores to the microbial metabolic processes as a part of a bigger microcosm experiment. In particular, we examined enzymatic activities of the bacterial species playing a key role in microbial degradation of ctenophore organic detritus (Vibrio splendidus ter Pseudoalteromonas). We compared these results to the activities of the enzymes from the microbial species which are usually not an important part of the marine microbial community (Pseudomonas sp., Vibrio campbelli in Zunongwangia profunda). The affinities of the chosen enzymes from the aforementioned bacterial species that we determined during the experiment do not confirm the hypothesis claiming that synthetic protein substrates, similar to the natural ones from the ctenophore detritus, are most effectively decomposed by the extracellular proteases, excreted by the bacteria which degrade detritus in their natural habitat. What we did confirm is that glycosidases from the carbohydrate-rich phytoplankton remains-degrading bacteria are usually the most active in the presence of carbohydrate substrates. Since detritus does not contain chitin and contains very low concentrations of lipids, enhanced chitinase activity was sporadic and we could not determine olease activity at all. The consequence of the bacterial degradation of gelatinous zooplankton detritus is the release of organic and inorganic degradation products, concentrations of which we determined as well. We also studied the response of the microbial community to the presence of ctenothore detritus and detected an increase of all bacterial species, the ones that degrade detritus as well as the one that do not. While studying remineralisation, we detected the expected trend showing the initial consumption of labile organic products and limiting nutrients and the conversion of organic products into the inorganic ones.
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