Fine-scale biochemical variation in Fucus serratus (Phaeophyceae): Point sampling vs bulk samples and implications for industrial applications

Abstract EU policies on nature restoration and sustainability open the door for Fucus cultivation, however, based on the applications of the biomass, industry will have to explicitly account for spatiotemporal fluctuations in biochemical profiles. In general, brown seaweeds show high levels of biochemical variation, adjusting polysaccharide, protein, lipid, and secondary metabolite profiles in response to physiochemical factors and biological interactions, which vary geographically and seasonally. Therefore, in this study we examined the fine-scale spatial variability in two high value components, the total phenolic and protein content of Fucus serratus across three sites in Strangford Lough, Northern Ireland at two timepoints. We assessed how sampling either homogenised bulk or point sampling of thalli could impact detection of variability on an inter- and intra-site scale in August 2024 and February 2025, finding a significant effect on the detection of fine-scale variation in biochemical composition. Homogenised bulk samples were able to display clearer relationships, with February collected samples always possessing a higher protein and phenolic content than August samples. Point sampled thalli displayed high variability, capturing the fine-scale intra-site and intra-specific variation. Homogenisation of biomass delivered a more reliable and reproducible assessment of F. serratus biochemical composition at fine-scale, balancing sensitivity to broad patterns (such as seasonal shifts) with robustness against the high variability observed in single-thallus measurements. Developing this sampling protocol can help deliver actionable, site-scale predictions of yield and metabolite trends, ensuring consistent bioproduct quality.