The continued development of the aquaculture industry is contributing to the proliferation of artificial structures in the marine environment. Observations of seaweed farms (infrastructure and biomass) suggest they act as a habitat for associated species. Seaweed farms differ from other forms of artificial infrastructure as the material deployed already has marine organisms (i.e. culture species) growing on it. This ‘priming’ of ropes with juvenile sporophytes may affect future development of communities by facilitating colonizing species or suppressing competitors. We call this process ‘ecological priming’: the provision of a biological platform that influences the successional development of specific communities. The communities that developed on ropes primed with Alaria esculenta individuals were compared with unprimed ropes to assess the ecological priming effect, at a commercial kelp farm in south-west Ireland. Species richness increased over two cultivation seasons and species composition was consistent between years, with distinct communities developing on primed and unprimed treatments. Timing of species occurrence on primed ropes was predictable with no predictable pattern occurring on unprimed ropes. Multivariate tests indicated distinct communities between treatments, with suppression of other algal species and potential facilitation of some species that have a particular association with A. esculenta on primed ropes. Communities from primed holdfasts contained a lower diversity of algal species compared with unprimed communities. Cultivated kelp holdfasts represent a habitat for distinct assemblages that reflect ecological priming of the substratum.

All habitats are modified to some extent by the species that live within them. Kelp is known to have a very strong influence on the surrounding environment providing a habitat for a wide range of organisms including marine mammals, fish and invertebrates. Here we examine the consequences of a subtle shift in the relative abundance of two species of kelp, Laminaria digitata and Laminaria ochroleuca, and compare the holdfast epibiont assemblages on both. These species are morphologically very similar and both provide important biologically generated habitats. The distribution of these kelp species is predicted to alter as a consequence of climate change with L. ochroleuca extending its range northward and potentially outcompeting L. digitata in the north-eastern Atlantic. The epibiont fauna common to both species of kelp were predominantly made up of annelids, molluscs and bryozoans. Most of the epibiont flora we found on the holdfasts was from the class Rhodophyceae. Multivariate analysis showed that the richness of epibiont species associated with L. ochroleuca was significantly lower, a mean of 0.62 species per cm3, when compared to the northern species, L. digitata which had a mean of 1.13 species per cm3. Laminaria digitata also had more unique epibiont species indicating that species richness of holdfast assemblages is likely to decline if L. digitata is replaced by L. ochroleuca. These data illustrate the importance of studying biologically generated habitats when considering the potential consequences of climate change on marine assemblages.