Seaweed Essential Oils as a New Source of Bioactive Compounds for Cyanobacteria Growth Control: Innovative Ecological Biocontrol Approach

The application of natural compounds extracted from seaweeds is a promising eco-friendly alternative solution for harmful algae control in aquatic ecosystems. In the present study, the anti-cyanobacterial activity of three Moroccan marine macroalgae essential oils (EOs) was tested and evaluated on unicellular <i>Microcystis aeruginosa</i> cyanobacterium. Additionally, the possible anti-cyanobacterial response mechanisms were investigated by analyzing the antioxidant enzyme activities of <i>M. aeruginosa</i> cells. The results of EOs GC-MS analyses revealed a complex chemical composition, allowing the identification of 91 constituents. Palmitic acid, palmitoleic acid, and eicosapentaenoic acid were the most predominant compounds in <i>Cystoseira tamariscifolia, Sargassum muticum</i>, and <i>Ulva lactuca</i> EOs, respectively. The highest anti-cyanobacterial activity was recorded for <i>Cystoseira tamariscifolia</i> EO (ZI = 46.33 mm, MIC = 7.81 μg mL^-1, and MBC = 15.62 μg mL^-1). The growth, chlorophyll-<i>a</i> and protein content of the tested cyanobacteria were significantly reduced by <i>C. tamariscifolia</i> EO at both used concentrations (inhibition rate >67% during the 6 days test period in liquid media). Furthermore, oxidative stress caused by <i>C. tamariscifolia</i> EO on cyanobacterium cells showed an increase of the activities of superoxide dismutase (SOD) and catalase (CAT), and malondialdehyde (MDA) concentration was significantly elevated after 2 days of exposure. Overall, these experimental findings can open a promising new natural pathway based on the use of seaweed essential oils to the fight against potent toxic harmful cyanobacterial blooms (HCBs).