Standardized 16S Meta-Analysis Reveals Consistent Host-Associated Patterns in Laminariales Epiphytic Microbiomes.

Macroalgae and their associated microbes form tightly integrated holobionts, yet cross-study comparisons of epiphytic microbiomes remain constrained by heterogeneous sampling designs, primer selection, and analytical pipelines. We performed a harmonized meta-analysis of publicly available 16S rRNA gene datasets to examine diversity, community structure, and inferred functional profiles within a common analytical framework. A structured search identified 16 studies, totaling 763 samples, from macroalgae and adjacent seawater across four oceanic regions. All datasets were reprocessed using a standardized workflow to ensure cross-study comparability. The compiled dataset was strongly skewed towards brown macroalgae (Phaeophyceae) and the V4 region of the 16S gene, highlighting both the prominence of Laminariales in current research and the need for methodological harmonization. Within this framework, alpha diversity differed among macroalgal orders, with Fucales hosting the richest epiphytic assemblages, Desmarestiales intermediate diversity, and Laminariales the lowest, while seawater exhibited intermediate values. Community composition was structured by host taxonomic identity and sample type. Within Laminariales, thalli supported assemblages distinct from seawater, sharing a limited taxonomic core and displaying reproducible genus-level signatures. Trait-based functional annotation indicated enrichment of aerobic chemoheterotrophy and polysaccharide-associated metabolisms in Laminariales communities, whereas seawater showed greater representation of nitrogen- and sulfur-related processes. These findings demonstrate that cross-study reprocessing resolves consistent host-associated patterns and establishes a quantitative framework for future multi-omics and experimental investigations.