Bacterial associations with the hydromedusa Nemopsis bachei and scyphomedusa Aurelia aurita from the North Atlantic Ocean

Recent studies suggest that jellyfish influence the community composition of marine microorganisms, but few studies have been conducted contrasting communities among different jellyfish taxa. In this study microbial communities were compared between two cnidarians found in North Atlantic Ocean coastal waters during the spring–summer months. Microbial communities associated with the invasive hydrozoan Nemopsis bachei and the cosmopolitan scyphozoan Aurelia aurita (Cnidaria) were characterized based on the 16S rRNA gene sequence. The bacterial communities associated with the jellyfish were significantly different from the communities in seawater, and N. bachei and A. aurita hosted taxon-specific bacterial groups. Gammaproteobacteria, Bacteroidetes and Alphaproteobacteria dominated bacterial sequences on N. bachei, the dominant orders including Vibrionales, Flavobacteriales, Rhizobiales and Rickettsiales. Vibrio spp. and Photobacterium spp. were abundant in N. bachei, and Tenacibaculum sp. (Bacteroidetes) had a host-specific association with N. bachei. Mycoplasmatales was a prominent, unique, and potentially host-promoted association in A. aurita, and overall Cyanobacteria, Tenericutes and unclassified bacteria dominated the sequences in A. aurita. This is the first description of the microbial community composition in N. bachei, which has been reported as an invasive species in eastern North Atlantic waters. Overall these results suggest that different cnidarians in North Atlantic coastal waters promote growth of distinct microbial communities. Jellyfish could thus differentially influence microbially mediated biogeochemical cycles and food webs in regions where they proliferate.