Multiscale spatial variability in epibiont assemblage structure associated with stipes of kelp Laminaria hyperborea in the northeast Atlantic

Foundation species elevate local biodiversity and underpin critical ecological processes and functions. Kelp species are distributed along ~25% of the world’s coastlines, where they serve as foundation species in intertidal and subtidal habitats. As well as ameliorating environmental conditions and producing organic matter, they provide biogenic habitat for a vast array of associated organisms. Here, we investigated patterns of diversity and structure in assemblages associated with the stipe of the kelp Laminaria hyperborea in the NE Atlantic. Stipes were sampled at 4 study regions (with 3 sites nested within each region) in the UK, spanning ~9° of latitude. Stipe-associated communities were highly diverse (134 species) and abundant (16-4532 ind. stipe-1), with no obvious sequential shift in diversity or overall trends in abundance/biomass of assemblages with latitude. However, we observed high degrees of variability between sites from the same region and individuals within sites, indicating that processes working across smaller spatial scales were more important than those at regional scales. While we observed high between-site variability in assemblage structure, regional differences were also evident. Most notably, sites within our southernmost region (southern England) were largely devoid of amphipods that dominated all other regions. This study highlights the important role of L. hyperborea in elevating biodiversity at local to regional scales through a facilitative interaction. Moreover, given that L. hyperborea forests may be increasingly impacted by ocean warming, changes in coastal water quality and proposed exploitation, our study serves as an important benchmark against which to detect future changes