‘Hanging gardens’—comparing fauna communities in kelp farms and wild kelp forests

Abstract

A growing need for food is causing increased interest for seaweed farming globally. This requires the knowledge of the industry’s effects on the marine environment. We therefore aimed to explore the communities hosted by a kelp farm compared to that of wild kelp forests. The study was performed in mid-western Norway. Kelp associated fauna were collected from farmed kelp (Saccharina latissima and Alaria esculenta), in wild kelp forests (S. latissima, A. esculenta, and Laminaria hyperborea), and from fauna traps in the water column. The study showed that the kelp farm had lower taxa abundance and richness and a lower biodiversity than the wild kelp forests. Nonetheless, the farmed kelp hosted many associated species, with communities different from what was found on ropes without kelp (i.e., in the water column). The fauna communities among the farmed kelp were more similar to what was found in the wild L. hyperborea kelp forest than to its wild counterparts. The difference between the fauna communities of ‘old’ and ‘young’ farmed kelp (grown for 3 and 7 months, respectively) was not significant, but the fauna was dominated by the isopod species Idotea pelagica in the young forest and by amphipods, mainly belonging to the genus Caprella, in the older. The study contributes to our knowledge of kelp farms’ ecological role in the marine environment, which is of importance for today’s management as well as for ensuring a sustainable future development of the kelp farming industry.

Home sweet home: Comparison of epibiont assemblages associated with cultivated and wild sugar kelp (Saccharina latissima), co-cultivated blue mussels (Mytilus edulis) and farm infrastructure

“…2020; Walls et al 2016, 2017, 2019) and wild plants (Arnold et al 2016; Bekkby et al 2023; Bué et al 2020; Salland and Smale 2021; Teagle et al 2018;Walls et al 2016). This study also supports recent ndings that kelp farms in Europe form distinct habitats to wild kelp forests, as there were consistent differences in epibiont assemblage structure and taxa richness between farmed and wild kelps(Bekkby et al 2023;Walls et al 2016). In Ireland, species richness was higher on cultivated rather than wild Laminaria digitata holdfasts(Walls et al 2016), whereas in Porthallow Bay, farmed kelps supported lower taxa richness per kelp than wild kelps, despite overall taxa richness at the Porthallow farm being comparable to the wild sites in August.…”

“…A study in Ireland compared unseeded, or bare ropes, to those seeded with A. esculenta and found different epibiont assemblages between them, indicating that cultivated kelps offer distinct habitat and potentially suppress other algae from settling (Walls et al 2019). Similarly in Norway, farmed kelp and bare ropes hosted distinct faunal assemblages (Bekkby et al 2023), highlighting how farm infrastructure alone may in uence habitat provisioning at aquaculture sites.…”

“…epibiont taxa present in this study were consistent with those previously recorded on kelp plants at the farm in Porthallow Bay(Corrigan et al 2023), as well as studies conducted elsewhere at comparable sites in Europe on both farmed (Bak, Mols-Mortensen, and Gregersen 2018; Bekkby et al 2023; Forbord et al 2020; Førde et al 2016; Peteiro and Freire 2013; Rolin et al 2017; Visch, Kononets, et al 2020; Visch, Nylund, et al In Norway, entire plants of both S. latissima andA. esculenta exhibited lower faunal richness and lower overall biodiversity than wild kelp plants after both three and seven months of cultivation(Bekkby et al 2023). Similarly, in Porthallow Bay, epibiont assemblages on farmed kelp did not become more similar to those associated with wild kelp plants following an additional three-month growth period beyond their typical harvest time, suggesting that dissimilarity between assemblage types is persistent at the time frames studied.Farmed kelp assemblages may be distinct from those hosted by wild kelps for several reasons.…”

“…The difference in results between these studies may be due to the different kelp species or regions investigated, or because only assemblages associated with holdfasts were examined in Ireland, whereas assemblages associated with entire plants were examined here. depths (due to tides) and are often attached to xed, stable substrate, resulting in a very different hydrodynamic environment(Bekkby et al 2023;Walls et al 2016). Suspended farmed kelps are also isolated, to some extent, from benthic habitats so that less dispersive species (e.g.…”

Integrating environmental and ecological monitoring with seaweed farming

“…They can improve water quality through biofiltration and serve as a food source for benthic organisms when they dislodge from the seaweed farm canopy and settle on the ocean floor [16], [17]. In the northeast Atlantic context, studies indicate that cultivated seaweed environments may equal or surpass the biodiversity found in their natural counterparts by offering ‘hanging gardens’ as an alternative suspended living space for marine organisms [18], [19].…”