This thesis represents the first landscape for understanding of the bacterial community associated with jellyfish, with special emphasis on ctenophore and scyphomedusae, at Helgoland Roads in the German Bight (North Sea). Bacterial community associated with the frequently occurring ctenophore species Mnemiopsis leidyi, Beroe sp., Bolinopsis infundibulum and Pleurobrachia pileus were investigated. Species-specific difference regarding the different ctenophores is revealed in present study. The bacterial communities of all ctenophore species were dominated by Proteobacteria as revealed by pyrosequencing. M. leidyi and P. pileus mainly harbored Gammaproteobacteria, with Marinomonas being the dominant phylotype of M. leidyi. This results also obtained from the Tampa Bay of Florida and the Gullmar fjord at the west coast of Sweden were confirmed by our study, suggesting ctenophores from geographically distinct regions shared high similarity in their dominant bacterial communities. In contrast, in P. pileus, Pseudoalteromonas and Psychrobacter were the dominating phylotypes of Gammaproteobacteria. Beroe sp. was mainly dominated by Alphaproteobacteria, particularly by the genus Thalassospira. For B. infundibulum, the bacterial community is comprised of Alphaproteobacteria and Gammaproteobacteria in equal parts consisting in particular of the genera Thalassospira and Marinomonas. Seasonal variation of bacterial community is observed in M. leidyi on a small scale. Regarding the typical metagenetic life cycle of scyphomedusae, the bacterial communities associated with two scyphomedusae species (Cyanea lamarckii and Chrysaora hysoscella) was firstly investigated at Helgoland Roads (North Sea, Germany) regarding with both different body parts and different life stages. Concerning the analysis of different body parts (umbrella, gonad, tentacle and mouth arm), significant differences are revealed between umbrella and other body parts (gonad and tentacle) in terms of the associated bacterial community in both species. With regarding to the different life stages, bacterial community structure varied from the early stage planula larva to polyp even to adult medusa with significant differences in both species with completely distinct patterns. A passive substrate colonized by diverse bacterial community presenting a dispersive structure among three life stages in C. lamarckii, while a strong selected processed of bacterial colonization in each life stage presenting a highly separated community structure in Ch. hysoscella. Furthermore, the impact of the food source on the associated bacterial community was investigated with polyp. Bacterial communities associated with polyps were significantly distinct from that with food in both species. Interestingly, the diversity of BCC associated with polyps was highly correlated with different food sources. However, for the bacterial community composition, significant differences were presented in response to different food source. Polyps might react differently during metabolism processing in response to different food source (A. salina and plankton) resulting in a significantly different bacterial community structure. In generally, the bacterial communities associated with two scyphomedusae species are species-specific confirmed in each life stage. In the third part of this thesis, the utilization of DOM released by live jellyfish was firstly investigated. We focused on the compositional succession of bacterioplankton community in response to the DOM released by live scyphomedusae (Cyanea lamarckii and Chrysaora hysoscella). Bacterial communities were significantly different regarding to different DOM source including jellyfish treatment (released by live jellyfish), “Kabeltonne” seawater (natural DOM from seawater) and artificial seawater (DOM-free). The bacterial community was significantly stimulated by the DOM released by live jellyfish with different dominant phylotypes regarding to different scyphomedusae species. Gammaproteobacteria and Bacteroidetes were consistent present in the experiment conducted with Ch. hysoscella, while Bacteroidetes decreased at the beginning and recovered at the end of the experiment conducted with C. lamarckii. The significant differences in the bacterial community composition and succession indicate that the DOM released by jellyfish might be consisted of different compounds which are species specific. Last but not the least, current study clearly showed that the bacterioplankton community not only influenced by the degradation of jellyfish biomass, but also strongly impacted by DOM released from live jellyfish in corresponds to the metabolic process of jellyfish.