Light Spectra, a Promising Tool to Modulate Ulva lacinulata Productivity and Composition

Light quality is a key factor affecting algal growth and biomass composition, particularly pigments such as carotenoids, known for their antioxidant properties. Light-emitting diodes (LEDs) are becoming a cost-effective solution for indoor seaweed production when compared to fluorescent bulbs, allowing full control of the light spectra. However, knowledge of its effects on <i>Ulva</i> biomass production is still scarce. In this study, we investigated the effects of LEDs on the phenotype of an <i>Ulva lacinulata</i> strain, collected on the Northern Portuguese coast. Effects of white (W), green (G), red (R), and blue (B) LEDs were evaluated for growth (fresh weight and area), photosynthetic activity, sporulation, and content of pigments and antioxidant compounds. The results showed that there were no significant differences in terms of fresh weight accumulation and reduced sporulation among the tested LEDs, while W light induced the highest expansion rate. Under G, <i>U. lacinulata</i> attained a quicker photoacclimation, and the highest content of pigments and total antioxidant activity; but with R and W, antioxidant compounds against the specific radicals O₂^•- and ^•NO were produced in a higher content when compared to other LEDs. Altogether, this study demonstrated that it is possible to modulate the bioactive properties of <i>U. lacinulata</i> by using W, R, and G light, opening the path to the production of biomass tailored for specific nutraceutical applications.