Bacteria on Laminaria hyperborea: Spatial Patterns and Tissue-Specific AssemblagesReef-associated Biodiversity

Harry Catherall¹, Pippa Moore¹, Heather Sugden¹, Nathan King²

¹Newcastle University, UK - ²Marine Biological Association, UK

Kelps, large canopy-forming macroalgae, are foundational species that support diverse marine ecosystems and contribute significantly to coastal ecological processes. In the northeast Atlantic, Laminaria hyperborea dominates subtidal rocky reefs, offering habitat and resources for diverse associated communities. This study investigated the bacterial assemblages associated with L. hyperborea blades and holdfasts across sites within three locations along the northeast coast of England. Using 16S rDNA sequencing, we explored the diversity, structure, and functional assemblages of kelp-associated microbiomes. Results revealed strong microbial structuring by tissue type, with distinct assemblages on blades and holdfasts, and holdfast microbiome assemblages closely resembling those of rocky biofilms. Bacterial diversity and assemblage composition exhibited significant spatial variation across regions and sites, likely reflecting the influence of localised environmental conditions. Notably, blades harboured greater relative abundances of Planctomycetes and Alphaproteobacteria, taxa associated with bacterial decomposition and photosynthetic host interactions. These findings underscore the spatial complexity of kelp microbiome assemblages and the role of tissue-specific and regional factors in shaping microbial communities. These findings reveal the complexity and spatial variability of microbial assemblages associated with L. hyperborea, highlighting the importance of investigating microbial diversity as an integral part of understanding kelp forest ecosystems.