From waste to value: cultivating Palmaria palmata in liquid seafood side stream enhances its growth and nutritional composition

The red seaweed Palmaria palmata is a promising candidate for sustainable food production due to its unique nutritional and sensory properties. Using side streams from the seafood industry to cultivate seaweed is an innovative circular approach to return otherwise lost nutrients back into the food chain. Our study investigates the use of herring production process water (HPPW) as a cultivation medium to improve the growth and nutritional quality of P. palmata in land-based systems. We identified the most favorable salinity and irradiance conditions (22.5PSU and 180 μmol photons m−2 s−1) as well as the dilution level of HPPW (40 μM NH4+) to establish optimal cultivation conditions. When P. palmata was cultivated under these optimized conditions, it significantly improved growth rates, tissue nitrogen content, pigments, and total amino acid levels, including all essential amino acids in levels exceeding dietary recommendations. The toxic and potentially toxic elements arsenic, inorganic arsenic, mercury, lead, and cadmium did not limit the safe daily intake of the biomass, instead, iodine was the limiting factor restricting safe daily consumption of HPPW-cultivated P. palmata to 23 g dry weight. A portion of this size could make a valuable contribution to macro- and trace element intake, providing approximately 63 % of the recommended daily intake for potassium, 22 % for magnesium, and 17 % for copper. Together, these findings show that P. palmata has a strong potential as an alternative food source in sustainable food systems when cultivated under optimized land-based conditions and supplemented with repurposed liquid seafood industry side streams.