Bioactive Coatings and Engineered Settlement Interfaces for Artificial Coral Reefs: A Systematic Review of Advances, Challenges, and Future Perspectives

The use of concrete in artificial reefs presents a “recruitment paradox”: its inherent hyperalkalinity and delayed natural neutralization severely impair coral larval settlement. Functional surface coatings can mitigate this cytotoxicity and actively provide biological settlement cues. Following PRISMA 2020 guidelines, this systematic review evaluates 16 years of experimental evidence on cementitious surface modifications across Web of Science, Scopus, and ScienceDirect up to September 2026. From 6436 screened records, 127 studies were assessed for full-text eligibility, with a strictly filtered subset of 12 experimental studies included for quantitative data extraction. To systematically categorize these technologies, we propose a novel dual classification framework mapping engineered interfaces by restoration approach (Classes I–IV) and Interfacial Activity Mode (A0–A4). The review evaluates relationships between coating architecture, bio-interfacial stability, and biological performance, identifying current technological bottlenecks. Addressing the need for scalable solutions, we propose a research roadmap integrating circular bioeconomy models and green biomaterials. Methodological quality was assessed by requiring biological validation of coatings in realistic larval settlement models, excluding purely theoretical material simulations. This systematic review was not prospectively registered. Ultimately, this materials-oriented framework clarifies bio-interfacial interactions and identifies research priorities for developing durable, biologically compatible substrates for coral reef restoration.