Antibiofilm and Antifouling Properties of Sargassum plagiophyllum (C. Agardh, 1824) Extract

Biofouling poses significant challenges to the maritime industry. While many commercial antifouling agents are effective, their toxic effects on marine ecosystems have raised environmental concerns. To address this issue, this study aimed was to evaluate antifouling properties of Sargassum plagiophyllum extracts through a series of assays, including crystal violet antibiofilm activity, antibacterial screening, cytotoxicity evaluation, aquarium testing, and in situ field experiments. The methanolic crude extract of S. plagiophyllum demonstrated potent antibiofilm activity with an IC50 value of 0.014 mg/mL, while the aqueous fraction exhibited a higher IC50 of 0.690 mg/mL. Cytotoxicity assay using the brine shrimp lethality assay revealed that S. plagiophyllum crude extract indicated non-toxic action across various concentrations. S. plagiophyllum does not exhibit antibacterial activity against Pseudomonas aeruginosa but disrupts bacterial quorum sensing, as evidenced by the formation of a colorless opaque zone in Chromobacterium violaceum assay. Aquarium-based antifouling tests further demonstrated that a 5% formulation of S. plagiophyllum extract significantly reduced bacterial biofilm formation. Panels treated with the 5% S. plagiophyllum formulation exhibited a marked reduction in bacterial adhesion compared with the negative control. These results were comparable to those obtained with commercial antifouling paints: specific commercial antifouling formulations reference 1 (RF1) and reference 2 (RF2), which showed bacterial counts of 0.92×108 CFU/mL (p < 0.001) and 0.95×108 CFU/mL (p < 0.001), respectively. The active fractions identified several compounds, which likely contribute to the observed antifouling properties. In situ testing conducted in Redang Island and Kuala Kemaman, Malaysia, confirmed the efficacy of the 5% S. plagiophyllum formulation in reducing marine fouling over a three-month period, outperforming both RF1 and RF2. These findings highlight the potential of S. plagiophyllum as a sustainable and effective alternative for eco-friendly antifouling coatings on the environmental implications of using S. plagiophyllum.