A community perspective on the concept of 1 marine holobionts : current status , challenges , 2 and future directions 3 4 The Holomarine working group

89 Host-microbe interactions play crucial roles in marine ecosystems, but we still have very 90 little understanding of the mechanisms that govern these relationships, the evolutionary 91 processes that shape them, and their ecological consequences. The holobiont concept is a 92 renewed paradigm in biology that can help to describe and understand these complex systems. It 93 posits that a host and its associated microbiota, living together in a stable relationship, form the 94 holobiont, and have to be studied together as a coherent biological and functional unit to 95 understand its biology, ecology, and evolution. Here we discuss critical concepts and 96 opportunities in marine holobiont research and identify key challenges in the field. We highlight 97 the potential economic, sociological, and environmental impacts of the holobiont concept in 98 marine biological, evolutionary, and environmental sciences with comparisons to terrestrial 99 sciences where appropriate. Given the connectivity and the unexplored biodiversity specific to 100 marine ecosystems, a deeper understanding of such complex systems requires further 101 technological and conceptual advances, e.g. the development of controlled experimental model 102 systems for holobionts from all major lineages and the modeling of (info)chemical-mediated 103 interactions between organisms. The most significant challenge is to bridge cross-disciplinary 104 research on tractable model systems in order to address key ecological and evolutionary 105 questions. This will be crucial to decipher the roles of marine holobionts in biogeochemical 106 cycles, but also developing concrete applications of the holobiont concept e.g. to increase yield 107 or disease resistance in aquacultures or to protect and restore marine ecosystems through 108 management projects. 109 110 PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.27519v3 | CC BY 4.0 Open Access | rec: 23 Aug 2019, publ: 23 Aug 2019