## 2 This Special Issue  
The present Special Issue covers review articles and research papers addressing the biological activities of marine resources which may present high applicability and potential for industrial purposes. From submissions, eight high-quality manuscripts were selected covering the above-mentioned topics. The importance of marine micro- and macroalgae, yeast, and even bacteriophages in the applied biotechnology field is evident from the well-split number of manuscripts presented here. The potential of microalgae strains as sustainable alternative sources for commercial lutein, known to help maintain normal visual function, was critically reviewed by [PERSON] and co-workers [1], who also address appropriate cultivation strategies and market challenges. The authors argue that microalgae can, in fact, be a competitive and sustainable natural source, presenting higher growth rates and not requiring arable land and/or a growth season, compared to marigold flowers, the predominant natural source of lutein. [PERSON] and co-workers [2] focused their work on the premise that diatoms are potential added-value biorefineries producing unique pigments, triglycerides (TAGs), and long-chain polyunsaturated fatty acids (LC-PUFAs), with potential applications for feed, food, or even biofuel industries. This manuscript describes how pigments and fatty acid production in the diatom _Phaeodactylum tricornutum_ can be modulated by spectral light control during their growth and contribute towards a better cultivation of these organisms for biotechnological purposes, and additionally discuss how diatoms may use such mechanisms to efficiently regulate light absorption and cell buoyancy. [PERSON] and co-workers [3] argue that the microalgae _Isochrysis galbana_ offers a broad range of bioactive compounds such as carotenoids, PUFA, and antioxidants, but most of current extraction solutions use toxic solvents, which causes environmental concerns. In their work, they optimized a method for the enhanced extraction of bioactive compounds from this species, using green technology of supercritical fluid extraction and applying a Box-Behnken design, presenting this methodology as a relevant and sustainable alternative to obtain important functional ingredients to be used in food and nutraceuticals. To obtain a sustainable alternative to fish oil and to find natural alternatives for pigments to be used in animal nutrition, [PERSON] and co-workers [4] propose Rhodotorula strains in their work, which were isolated from seawater, for the biosynthesis of docosahexaenoic acid (DHA) and canthaxanthin using a low-cost source of carbon. The results presented are the foundation to use sustainable and low-cost growth media, in a circular economy framework, to potentially scale the production and provide novel sources of these essential nutrients. Two studies were submitted proposing the seaweed _Grateloupia turuturu_ as a potential source of bioactive compound. This seaweed is considered an invasive species in Europe, although it is known to contain a myriad of bioactive secondary metabolites with different potentialities. Invasive species have damaging effects on the environment and, by adding value to this biomass, the harvesting industry will contribute to control and even restore impacted environments, thus turning these threats into opportunities [5]. [PERSON] and co-workers [6] addressed the development of green and cost-effective extraction protocols to optimally obtain UV-shielding and antioxidant compounds from _G. turuturu_, using response surface methodology, and evaluated the effect of ethanol concentration, liquid-solid ratio, pH, temperature, and time to enhance bioactive compound extraction. They argue that these protocols will allow for an optimized and sustainable use of this marine resource, contributing to the potential development of natural and eco-friendly cosmeceuticals from low-cost biomass.