FIGURE 4.

Sustaining the rare: schematic view of macroorganisms, and especially fishes, as key contributors of microbial diversity maintenance. As highlighted in the main text, macroorganisms are expected to participate in the maintenance of marine microbial diversity by favoring certain rare taxa in seawater and sediment microbial communities but also through their horizontal and vertical transfer capacities. Full arrows depict transfer of microbes through trophic processes and dashed arrows depict microbial release from macroorganisms and passive processes. Gray arrows correspond to macroorganisms’ horizontal and/or vertical transfer potential. Asterisks on the abundance distributions represent the two types of host-associated microbes discussed in the main text, symbionts/mutualists (blue) and opportunist copiotrophs (red). Interrogation points depict ecosystem compartments for which there is currently not enough available data to generalize the proposed mechanisms of macroorganisms impact on microbial diversity.