(1) Background: To increase the biochemical productivity and to reduce the production cost of microalgal biodiesel, this study aimed to investigate the effects of CO₂ on biomass, fatty acids, carbon-hydrogen, and biochemical accumulation of the marine diatom, Amphora coffeaeformis RR03 (A. coffeaeformis) RR03. (2) Methods: Fatty acid composition of the dry biomass of A. coffeaeformis RR03 was analysed using Gas chromatography-mass spectrometry (GC-MS). (3) Results: The results showed that A. coffeaeformis RR03 contained high biomass productivity and biochemical composition in different cultivation conditions. A. coffeaeformis RR03 showed maximum growth of 5.2 × 10⁶/mL on 21st day cultivation under CO₂ supply. The bio-crude oil production from A. coffeaeformis RR03 was 36.19 megajoule (MJ). GC-MS analysis found that the dry biomass of A. coffeaeformis RR03 contained maximum of 47.72% fatty acids of 16-octadecanoic acid methyl ester (10:12) and 19.58% pentadecanoic acid, 13-methyl-, and methyl ester (9.24). (4) Conclusion: The results of this study may suggest that a novel diatom of A. coffeaeformis RR03 could be a suitable candidate for biocrude production in order to meet the future demand of energy.

Four different strains of marine algae viz. Tetraselmis tetrathele, Tetraselmis striata, Tetraselmis chuii, and Tetraselmis gracilis were isolated from the saltpans in Kovelong, Chennai, Tamil Nadu, India. The systematic position of Tetraselmis striata BBRR1 was confirmed through molecular identification. Under laboratory conditions, T. striata Butcher BBRR1 grown in f/2-medium recorded highest biomass concentration of 0.58 ± 0.021 g L⁻¹, volumetric productivity of 0.025 ± 0.004 g L⁻¹ d⁻¹, 19 ± 2.3% proteins, 17 ± 1.5% carbohydrates, and 15 ± 2.4% lipids. Volumetric biomass productivity of 0.063 ± 0.08 g L⁻¹ d⁻¹, specific growth rate of 0.45 day⁻¹ and lipid content of 19.42 ± 0.98% were recorded for the alga T. striata Butcher BBRR1 cultivated in 10-m² open raceway ponds using Modified CFTRI ABRR1 medium. The fatty acid profile of T. striata Butcher BBRR1 showed the presence of 33.14% palmitic acid, 22.64% 11-octadecenoic acid, and 21.94% heptadecanoic acid. This study confirms the feasibility of cultivating the marine alga T. striata in open raceway ponds to produce biomass, which can be used for the production of biofuels.