Roughness-dependent exploration strategies regulate barnacle cyprid settlement on titanium surfaces

Increasing TA2 roughness induces a non-monotonic trend in barnacle settlement • Moderate roughness promotes exploration and protein deposition to enhance settlement • Excessive roughness triggers rapid settlement but limits pheromone dispersal • Surface roughness regulates cyprid settlement even in the presence of biofilm . The widespread use of titanium in marine structures is hindered by its susceptibility to biofouling. As a promising antifouling approach, the rational design of direct surface modification relies on a fundamental understanding of how surface properties regulate the settlement of fouling organisms. Herein, this study investigated the effect of TA2 titanium surface roughness on the settlement process of barnacle cyprids. Increased roughness enhanced the temporary attachment of cyprids through sacrificial bonds and mechanical interlocking of deposited footprint proteins. A moderate roughness increase facilitated more surface exploration and footprint protein deposition, thus likely enhanced the distribution of settlement-inducing protein complex (SIPC, a key settlement pheromone), thereby increasing the final settlement ratio. In contrast, excessive roughness enabled cyprids to locate favorable settlement sites with minimal surface exploration, leading to localized surface inspection, increased footprint protein area, and reduced coverage, which may lead to a concentration-dependent avoidance response and reduced cyprid-protein contact probability, resulting in a plateau in the settlement ratio. Field experiments further confirmed that direct cyprid-substrate contact is a prerequisite for firm settlement even in the presence of biofilm, consistent with the mechanistic insights obtained from laboratory assays. These findings elucidate roughness-dependent exploration strategies of barnacle cyprids and provide a theoretical basis for designing antifouling TA2 for marine applications.