Enhancing Bioproducts in Seaweeds via Sustainable Aquaculture: Antioxidant and Sun-Protection Compounds

Abstract

Marine macroalgae are considered an untapped source of healthy natural metabolites and their market demand is rapidly increasing. Intertidal macroalgae present chemical defense mechanisms that enable them to thrive under changing environmental conditions. These intracellular chemicals include compounds that can be used for human benefit. The aim of this study was to test cultivation protocols that direct seaweed metabolic responses to enhance the production of target antioxidant and photoprotective biomaterials. We present an original integrated multi-trophic aquaculture (IMTA) design, based on a two-phase cultivation plan, in which three seaweed species were initially fed by fish effluents, and subsequently exposed to various abiotic stresses, namely, high irradiance, nutrient starvation, and high salinity. The combined effect of the IMTA's high nutrient concentrations and/or followed by the abiotic stressors enhanced the seaweeds' content of mycosporine-like amino acids (MAAs) by 2.3-fold, phenolic compounds by 1.4-fold, and their antioxidant capacity by 1.8-fold. The Sun Protection Factor (SPF) rose by 2.7-fold, and the chlorophyll and phycobiliprotein synthesis was stimulated dramatically by an order of magnitude. Our integrated cultivation system design offers a sustainable approach, with the potential to be adopted by emerging industries for food and health applications.

Keywords: Gracilaria; Ulva; antioxidants; bioproducts; integrated aquaculture; mycosporine-like amino acids; phenolic compounds; pigments; seaweeds; sun protection factor.

Figure 1

Mycosporine-like Amino Acids (MAAs) content (mg g⁻¹ DW), for Gracilaria conferta (red) and Hypnea musciformis (blue), cultivated under the different culture conditions. SW (seawater). Statistical analysis was performed for each species separately. Different letters indicate significant differences (uppercase letters: Gracilaria, lowercase: Hypnea).

Figure 2

MAA proportions (%) for Gracilaria conferta (a) and Hypnea musciformis (b), cultivated under different culture conditions. SW (seawater).

Figure 3

Antioxidant activity (µg TE mg⁻¹ DW) for Ulva rigida (green), Gracilaria conferta (red), and Hypnea musciformis (blue), cultivated under the different culture conditions. SW (seawater). Statistical analysis was performed for each species separately. Different letters indicate significant differences (uppercase letters: Ulva, lowercase: Gracilaria, italics: Hypnea).

Figure 4

Phenolic content (μg PE mg⁻¹ DW) for Ulva rigida cultivated under the different culture conditions. SW (seawater). Different letters indicate significant differences.

Figure 5

Sun Protection Factor (SPF) for Ulva rigida (green), Gracilaria conferta (red) and Hypnea musciformis (blue), cultivated under the different culture conditions. SW (seawater). Statistical analysis was performed for each species separately. Different letters indicate significant differences (uppercase: Ulva, lowercase: Gracilaria, italics: Hypnea).

Figure 6

Layout of the experimental system: (a) integrated cultivation in the initial two weeks, (b) integrated cultivation in the third week, (c–e) third week environmental stresses.