A community perspective on the concept of marine holobionts: current status, challenges, and future directions

Host-microbe interactions play crucial roles in marine ecosystems, but we still have very little understanding of the mechanisms that govern these relationships, the evolutionary processes that shape them, and their ecological consequences. The holobiont concept is a renewed paradigm in biology that can help describe and understand these complex systems. It posits that a host and its associated microbiota, living together in a stable relationship, form the holobiont, and have to be studied together, as a coherent biological and functional unit, to understand its biology, ecology and evolution. Here we discuss critical concepts and opportunities in marine holobiont research and identify key challenges in the field. We highlight the potential economic, sociological, and environmental impacts of the holobiont concept in marine biological, evolutionary, and environmental sciences with comparisons to terrestrial science wherever appropriate. Given the connectivity and the unexplored biodiversity of marine ecosystems, a deeper understanding of such complex systems requires further technological and conceptual advances. For the marine scientific community, the most significant challenge is to bridge functional research on tractable and original model systems and global approaches addressing ecological and evolutionary questions. This will be crucial for establishing the roles of marine holobionts in biogeochemical cycles, but also developing concrete applications of the holobiont concept in aquaculture and marine ecosystem management projects.