Effects of Light Conditions on Biomass Production and Biochemical Composition of the Marine Diatom Thalassiosira weissflogii

The rapid development of aquaculture has led to a growing demand for live feed. Marine diatom Thalassiosira weissflogii is a high-quality larval feed due to its balanced nutrition and digestibility. The controlled regulation of light conditions is important for improving the cultivation efficiency and biochemical composition of marine microalgae. This study evaluated the effects of LED spectra, light intensity, photoperiod, and flashing frequency on algal growth and nutrient accumulation. The results showed that red light at 623 nm had the highest cell density of 1.746 × 106 cells/mL, which was 2.56-fold higher than that under green light, while blue light treatments resulted in relatively higher soluble sugar contents in the harvested biomass. A light intensity of 50 μmol·m−2·s−1 facilitated the accumulation of photosynthetic pigments, while high light intensities of 150 μmol·m−2·s−1 and 200 μmol·m−2·s−1 were optimal for lipid accumulation, with lipid content exceeding 34%. Under the 12L:12D photoperiod, relatively high contents of both lipids and proteins were observed. Flashing frequency produced particularly distinct responses. A flashing frequency of 90 Hz resulted in the highest biomass accumulation and markedly enhanced soluble sugar accumulation to 144.04 mg/g. Correlation analysis further indicated that increasing light intensity, photoperiod, and flashing frequency generally favored biomass and soluble sugar accumulation, whereas longer photoperiods and higher flashing frequencies were associated with reduced lipid accumulation. Volumetric productivity analysis further highlighted the potential of 18L:6D and low-frequency flashing (30–50 Hz) for lipid production. Precise light parameter regulation enables targeted improvement of biomass and nutrient accumulation in T. weissflogii, providing theoretical support and lighting optimization for its large-scale aquaculture feed cultivation.