Research progress on eco-friendly natural antifouling agents and their antifouling mechanisms

Biofouling can cause economic losses in the marine sector and adversely affect the environment. Antifouling coatings are special paints that prevent marine organisms from attaching to a surface, with different paints exhibiting different antifouling effects, such as broad-spectrum bactericidal effects, antilarval settlement, antibiofilm activity, and antibiological adhesion. However, traditional antifouling agents usually exert varying degrees of toxic effects on marine organisms or other effects on their metabolism when used for marine antifouling. For example, tributyltin exerts broad-spectrum bactericidal effects owing to its high toxicity. Therefore, natural antifouling agents with biocompatibility, low pollution, low toxicity, and nontoxic characteristics have received widespread attention in various fields. To investigate the effects of antifouling agents on the fouling materials produced by marine organisms adhering to and growing on marine steel structures such as ships, this review summarizes the general antifouling mechanisms of antifouling agents, mainly focusing on the effects of inhibitors on antibiofilm, antibacterial, and antialgal activity. Moreover, the current state of research in the field of green antifouling coatings is elaborated, primarily summarizing research on four types of natural antifouling agents, namely marine microorganisms, macroalgae, marine invertebrates, and terrestrial natural products. Finally, the review summarizes and discusses the directions for the development of marine antifouling coatings. Overall, this review indicates that many natural antifouling agents have potential commercial value and are expected to provide theoretical value for marine antifouling technicians in developing new and environmentally friendly antifouling agents.