Seasonal variations in the metabolite content and the antioxidant capacity of the brown seaweed Halidrys siliquosa (Sargassaceae) from northwest Ireland

Abstract: Seaweed exploitation is considered an important element of environmental sustainability strategies in the global context of coastal resource management. Even though only a few species are commercially harvested and processed, the exploration of less-studied forms could help meet recent sustainability targets and reduce pressure on commonly exploited species. Here, the metabolic attributes of the brown seaweed Halidrys siliquosa (Order Fucales, Family Sargassaceae) from a tidal pool in the northwest of Ireland were investigated over a 12-month period. The total lipid and soluble protein and carbohydrate contents of the biomass of H. siliquosa thalli were analysed along with the pigments fucoxanthin and β-carotene and antioxidant activity potential. Results showed some seasonal patterns. Notably, lipids (max. 143.1 mg g⁻¹ DW) and β-carotene content (max. 2.8 mg g⁻¹) were higher in winter. Ethanolic extracts showed greater antioxidant capacity in winter and spring (> 1857.1 µmol Trolox eq. mg⁻¹ DW) with the FC assay. The monthly variations in the metabolic attributes of H. siliquosa were correlated to changes in environmental factors, including temperature and antioxidant activity as well as precipitations and carbohydrate and β-carotene content (P < 0.05). The peak metabolic contents in H. siliquosa occurred on different months of the year, making the identification of an optimal harvesting period difficult for this location. Yet, this species shows exploitation potential and would benefit from a tailored approach to being grown on novel aquaculture cultivation systems.