Biofouling propagation and its impact on non-biocidal antifouling coating performance evaluation under static and dynamic conditions

Biofouling significantly degrades vessel performance by increasing fuel consumption, harmful emissions (SO2, NOx, CO2), and maintenance costs, underscoring the role of effective fouling control coatings. However, the accuracy of antifouling coating performance assessments may be compromised by local fouling dynamics, particularly the influence of adjacent biofouled surfaces. This study investigates how proximity to pre-fouled panels coated with an epoxy primer affects biofouling settlement and growth on newly immersed coatings under both static and dynamic exposure conditions. Panels placed adjacent to heavily fouled surfaces exhibited accelerated colonization, with fouling coverage nearly doubling within three weeks compared to isolated controls. In static exposures, proximity led to the bypassing of early biofilm stages through lateral propagation via spores, sloughed fragments, and biofilm material. Under dynamic conditions, hydrodynamic forces amplified this effect, promoting faster dispersal and settlement, particularly of filamentous green and brown algae. These findings reveal that local propagation can significantly alter biofouling succession and growth rates, resulting in earlier community development and increased fouling intensity. Without careful spatial separation and test design, localized fouling pressure may be artificially elevated, leading to skewed interpretations of antifouling performance. Conversely, controlled propagation may serve as a tool for accelerated stress testing under high-biofouling conditions. This study emphasizes the need to account for biofouling propagation in experimental design to ensure reliable, reproducible antifouling evaluations.