The effect of light and nutrient availability on growth, nitrogen, and pigment contents of Saccharina latissima (Phaeophyceae) grown in outdoor tanks, under natural variation of sunlight and temperature, during autumn and early winter in Denmark

Late summer harvest of cultivated Saccharina latissima, prior to seasonally determined negative length growth, is considered advantageous in North Atlantic waters to optimize biomass yields. We hypothesized that seasonal increase in tissue protein and pigments over autumn and early winter would counterbalance the loss of biomass, and increase the absolute harvestable amount of protein and pigments. The hypothesis was tested in a land-based, factorial-designed, pilot-scale experiment using whole algae individuals exposed to naturally relevant high or low availability of nutrients and light. The experiment was conducted during fall/early winter in Grenaa, Denmark, in outdoor tanks, exposed to ambient light and temperature variations. With high nutrient availability, the absolute harvestable amounts of nitrogen, fucoxanthin, and chlorophyll a increased by 50.1–60.1, 21.7–53.7, and 47.0–73.5 %, respectively, despite a loss of biomass of 16.2–18.7 %. Under low nutrient availability, there was a net loss of biomass (8.1–9.5 %), tissue nitrogen (10.7–44.1 %), and fucoxanthin (7.1–17.2 %), and a minor increase in chlorophyll a (2.5–22.8 %). Nutrient availability had a significant negative impact on the biomass growth, but a positive control on the tissue concentration of nitrogen, chlorophyll a, and fucoxanthin. Our results, from a land-based experiment, indicate that early winter harvest of S. latissima biomass grown under high nutrient availability in Denmark, fulfills a higher degree of nutrient bioremediation, and has an improved biomass quality in regards of increased concentrations of pigments and nitrogen rich compounds.