Microbiomes of a Corallivore (Hermodice carunculata): Where in the Worm are the Coral Microbes?

The bearded fireworm, Hermodice carunculata , is a widespread annelid generally considered a nuisance species in reef environments and in aquaria alike as it feeds preferentially on members of the Phylum Cnidaria. As H. carunculata is a mobile corallivore, it has the potential to spread microbes by transporting them on its body surfaces and in its digestive tract. Here, we sequenced the V3-V4 16S ribosomal RNA region from four worm tissue types (anterior end, pharynx, posterior end with excrement, and middle body segments). We also characterized whole worms, substrates, diseased and healthy colonies of Montastrea cavernosa , in order to characterize the microbiome of the worm and its prey. Preliminary analyses suggest distinct microbial communities between the different tissue types and sections of the bearded fireworm as well as between the disease and healthy coral colonies. These initial results also indicate a higher number of pathogenic bacteria (e.g. Vibrio spp.) on the diseased coral and higher bacterial diversity in the substrate. The pharynx communities were primarily dominated by members of the Pseudomonadales and Flavobacteriales orders, while the middle and posterior ends contained higher proportions of Desulfobacterales. Since these annelids move between healthy and diseased coral colonies, determining the method and location of microbial abundance and exchange will lead to improved understanding of marine disease dynamics and mitigation efforts.