Bacterial communities of Cassiopea in the Florida Keys share major bacterial taxa with coral microbiomes

Interactions with microbial communities fundamentally shape metazoans’ physiology, development, and health across marine ecosystems. This is especially true in zooxanthellate (symbiotic algae-containing) cnidarians. In photosymbiotic anthozoans (eg. shallow water anemones and corals), the key members of the associated microbiota are increasingly well studied, but there is limited data on photosymbiotic scyphozoans (true jellyfish). Using 16S rRNA barcoding, we sampled the internal and external mucus of the zooxanthellate Upside- Down Jellyfish, Cassiopea xamachana and C. andromeda, throughout eight sites covering the full length of the Florida Keys. We find these medusae to have low-diversity internal microbial communities distinct from the communities of their external surfaces and their environment. These internal communities are dominated by only three taxa: Endozoicomonadaceae, Mycoplasmataceae, and Vibrionaceae. External mucosal samples conform largely to the communities of surrounding sediment with the addition of Endozoicomonadaceae. The microbial taxa we identify associated with wild Florida Keys Cassiopea bear a strong resemblance to those found within photosymbiotic anthozoans, increasing the known links in ecological position between these groups.