Reframing marine host-microbe symbioses: from taxonomic inventories to functional convergence

<jats:p>In October 2025, the Trends in Host-Microbe Symbioses Symposium at the University of Padova (Italy) brought together a global community of researchers, with the aim of taking stock of the current trajectory of marine host-microbiome research. Integrating perspectives from ecology, evolution, biogeochemistry, and biotechnology, the symposium documented a clear transition from descriptive surveys of microbial diversity toward a mechanistic understanding of host–microbe interactions. Across an unusually broad taxonomic spectrum – corals, sponges, fishes, molluscs, algae and seagrasses, cnidarians, acoels, arthropods and mammals - microbiomes were consistently framed as integral components of host biology, shaping nutrient cycling, development, immunity, and ecosystem function. Despite phylogenetic diversity across host groups, convergent functional processes (notably N and C cycling, stress buffering, immune priming, and metabolic complementation) emerged as a unifying framework, even though their taxonomic underpinnings remained system-specific. Advances in multi-omics, spatially resolved imaging (MALDI-MSI, NanoSIMS, FISH/CARD-FISH) and experimental microbiome manipulation are increasingly linking microbial identity to activity and function, enabling early predictive frameworks across scales. Collectively, the symposium laid the groundwork for microbiome-based interventions to enhance host resilience and support ecosystem conservation in a rapidly changing ocean.</jats:p>