Open water seaweed cultivation in the North Atlantic is currently dominated by well-established kelp species, Saccharina latissima (sugar kelp) and Alaria esculenta (winged kelp). Other fast-growing species have received comparatively little attention, including the pseudo-kelp Saccorhiza polyschides (furbelows), a high-yielding annual species native to the coastlines of western Europe that has been harvested and utilised by coastal communities for centuries. Despite its rich and diverse compositional profile and substantial application potential, commercial cultivation of S. polyschides remains limited to small research-scale sites in Portugal and lacking entirely from the northern extent of the species' diistribution.
Here we present findings from a two-year, high-resolution monitoring study perfomed at an experimental seaweed farm operated by the Scottish Association for Marine Science (SAMS) on the west coast of Scotland. Across two consecutive cultivation cycles (October–June 2023/24 and 2024/25), S. polyschides progression in growth, biomass yield, biochemical (% dry weight dwt of ash, total lipid, protein, and carbohydrate content; alginate; antioxidant activity), and elemental composition (%dwt C and N; trace metals) were followed, alongside continuous monitoring of key environmental cultivation conditions.
Growth dynamics and yield were similar across both cultivation cycles, with S. polyschides exhibiting exponential growth from mid-February to early June. Maximum weekly growth rates reached 2.3 kg wet weight per meter of growing line (kg wwt/m), corresponding to harvestable yields of up to 30±6 kg wwt/m. Biochemical and elemental composition varied throughout and across cultivation cycles as well as among tissue types i.e. frond, stipe, and holdfast; the latter of which are commonly excluded from processing. Total lipid and protein contents were highest in fronds, ranging from 3.5-5.9 and 4.4–12.2 %dwt, respectively. Other copmpounds however were significantly higher in stipes and holdfasts compared to fronds, with ash and alginate contents ranging from 56.5–71.8 %dwt and 18.0–23.9 %dwt in stipes, and 45.1–61.7 %dwt and 20.6–23.9 %dwt in holdfasts, respectively.
Seawater temperatures during Spring of the second cultivation cycle were significantly warmer than in previous years and included several marine heatwave (MHW) events. These conditions coincided with a delayed onset of the phytoplankton bloom and influenced the timing, extent, and composition of the biofouling communities associated with the growing seaweed.
Overall, our results demonstrate substantial achievable yields and favourable biochemical profiles, highlighting S. polyschides as a promising candidate for commercial cultivation and a range of applications such as food and feed, biostimulants and -fertilizer, and nutraceuticals. It offers a potential alternative to commonly farmed kelp species that may be increasingly vulnerable to ocean warming due to their narrow thermal tolerance. In addition, biomass that is currently undervalued or discarded (stipes and holdfasts) were shown to be rich in compounds of interest for the seaweed food and biostimulant markets. This study provides new insights into the cultivation potential of S. polyschides in cooler waters and identifies key lessons to further optimise production methods.
Acknowledgements
This study was funded under the EU H2020 project 'All Atlantic Ocean, Sustainable, Profitable and Resilient Aquaculture' [ASTRAL, grant ID: 863034; Sep 2020-24] and the NSF-UKRI/BBSRC funded International Bioeconomy & Macroalgae Center [IBMC; Jan 2025- Dec 2029].