Potential novel habitat created by holdfasts from cultivated Laminaria digitata: assessing the macroinvertebrate assemblages

Interest in the cultivation of native kelp species is increasing within Europe. Obser- vations of seaweed farms suggest that they may act as a habitat for associated species, potentially altering the richness of the local area. Previous studies have generally focused on species associ- ated with wild kelps, showing the holdfast to be relatively species-rich. Little research has, how- ever, been conducted on the species associated with cultivated kelps. The habitat created by cul- tivated kelp holdfasts may act as a novel habitat and not simply an expansion of existing kelp habitat, due to differences in holdfast age, holdfast morphology and holdfast position in the water column. Laminaria digitata from the west of Ireland were examined to test if these differences result in the fauna of cultivated (suspended) holdfasts being distinct from wild (benthic) stands. To place the results in a broader context, patterns were compared to holdfastrichness relationships observed in comparable studies from the NE Atlantic. Total abundance of holdfast epifauna was similar across benthic and suspended holdfasts from the west of Ireland, although species richness was higher in suspended samples. Richness and abundance in suspended kelp holdfasts were consistent with the range of values recorded in other wild kelp studies. There were significant dif- ferences in assemblage composition between holdfast types (ANOSIM; R = 0.383, p < 0.05). The distributions of faunal feeding types did not, however, vary between suspended and benthic kelps. Suspended holdfasts in the west of Ireland represented a novel habitat with higher species richness and a different species assemblage when compared to adjacent benthic kelps.