Marine biofouling communities increasingly develop on artificial marine structures associated with expanding port infrastructure and global shipping activity. These assemblages contribute to the spread of non-indigenous species and the restructuring of coastal biodiversity. However, the mechanisms governing spatial differentiation of fouling communities remain poorly understood, particularly the relative roles of nestedness and species turnover in shaping beta-diversity patterns. This study investigates spatial differentiation in marine biofouling assemblages using species occurrence records from 48 international ports collected between 2016 and 2023. Beta diversity was decomposed into nestedness and turnover components and linked to environmental gradients through multivariate ecological analysis and supervised machine-learning models. Results show that community differentiation is strongly dominated by nestedness processes, with a mean Jaccard dissimilarity of βjac = 0.267, while species turnover contributes minimally to compositional variation. Environmental analysis identifies turbidity and chlorophyll concentration as key predictors of fouling intensity, and machine-learning models achieve predictive accuracy above 0.82.