Salinity is an important abiotic factor since it is responsible for the local and/or regional distribution of algae. In coastal regions, salinity changes with prevailing winds, precipitation and tide, and particularly in extreme intertidal conditions. Acanthophora spicifera is a red seaweed that occurs in the supratidal region in which changes in abiotic conditions occur frequently. This study evaluated the effects of salinity on the metabolism and morphology of A. spicifera. Algae were acclimatized under culture conditions with sterilized seawater for seven days. Experiments used different salinities (15 to 50 psu) for seven days, followed by metabolic analyses. This study demonstrates that extreme salinities affect physiological parameters of A. spicifera, such as decrease in growth rate, as well as morphological parameters and concentrations of secondary metabolites. Acanthophora spicifera exhibited high tolerance to 25 to 40 psu, with little change in physiology, which favors the occurrence of this species in diverse environments. However, 15, 20, 45 and 50 psu were the most damaging and led to loss of biomass, depigmentation of apices, and the highest concentrations of antioxidant metabolites. The 50 psu treatment caused the greatest changes in general, greatly reducing a biomass and chlorophyll content, and facilitating the presence of endophytes.

Porphyra sensu lato has economic importance for food and pharmaceutical industries due to its significant physiological activities resulting from its bioactive compounds (BACs). This study aimed to determine the optimal nitrate dosage required in short-term cultivation to achieve substantial BAC production. A nitrate experiment using varied concentrations (0 to 6.5 mM) revealed optimal nitrate uptake at 0.5 mM in the first two days and at 3 and 5 mM in the last five days. Polyphenols and carbohydrates showed no differences between treatments, while soluble proteins peaked at 1.5 and 3 mM. Total mycosporine-like amino acids (MAAs) were highest in algae incubated at 5 and 6.5 mM, and the highest antioxidant activity was observed in the 5 mM, potentially related to the MAAs amount. Total carbon and sulfur did not differ between treatments, while nitrogen decreased at higher nitrate. This discovery highlights the nuanced role of nitrate in algal physiology, suggesting that biological and chemical responses to nitrate supplementation can optimize an organism’s health and its commercially significant bioactive potential. Furthermore, given its ability to absorb high doses of nitrate, this alga can be cultivated in eutrophic zones or even in out-/indoor tanks, becoming an excellent option for integrated multi-trophic aquaculture (IMTA) and bioremediation.

Porphyra sensu lato is one of the most economically significant and widely cultured and consumed algae in the world. Porphyra species present excellent nutraceutic properties due to their bioactive compounds (BACs). This research aimed to find the most efficient aqueous extraction method for BACs by examining alkaline and enzymatic hydrolysis. Alkaline hydrolysis with 2.5% sodium carbonate (SC) and at 80 °C proved optimal for extracting all BACs (phycobiliproteins, soluble proteins, polyphenols, and carbohydrates) except mycosporine-like amino acids (MAAs), which were best extracted with water only, and at 80 °C. Enzymatic hydrolysis, particularly with the ‘Miura’ enzymatic cocktail (cellulase, xylanase, glycoside hydrolase, and β-glucanase), showed superior results in extracting phycoerythrin (PE), phycocyanin (PC), soluble proteins, and carbohydrates, with increases of approximately 195%, 510%, 890%, and 65%, respectively, compared to the best alkaline hydrolysis extraction (2.5% SC and 80 °C). Phenolic content analysis showed no significant difference between the ‘Miura’ cocktail and 2.5% SC treatments. Antioxidant activity was higher in samples from alkaline hydrolysis, while extraction of MAAs showed no significant difference between water-only and ‘Miura’ treatments. The study concludes that enzymatic hydrolysis improves the efficiency of BACs extraction in P. linearis, highlighting its potential for the nutraceutical industry, and especially with respect to MAAs for topical and oral UV-photoprotectors.