Factors affecting the distribution of fouling assemblages in seawalls of a recreational marina of northern Portugal

Recreational marinas are increasing worldwide due to the growing demand for recreational boating. Although marinas generate chemical and physical disturbances, submerged artificial structures create new habitats for fouling assemblages. However, the factors shaping the distribution of these assemblages within marinas remain understudied.

To fill this gap, fouling assemblages on seawalls were studied in the recreational marina of Póvoa de Varzim (northern Portugal) in June 2026 using a hierarchical sampling design including two docks, two distances from the marina entrance (near and far), and two seawall orientations (north and south). Species cover was estimated at low tide using 50×50 cm quadrats. The influence of each factor on the richness and structure of fouling assemblages was assessed using univariate and multivariate analyses, while SIMPER routine was used to identify the species contributing to the observed differences.

Our results showed that assemblage structure was significantly affected by the interaction between distance from the marina entrance and orientation, whereas no significant effects were detected on species richness. Pairwise comparisons revealed significant differences between near and far locations only in the northern orientation. SIMPER analysis indicated an average dissimilarity of assemblages of ∼40 % between near and far sites. Of the 12 recorded taxa, nine contributed most to the observed differences, of which only turf algae and the barnacle Perforatus perforatus were exclusive or more abundant in near sites. Moreover, only two NIS, Watersipora subatra and Magallana gigas, were recorded in the far sites of the northern orientation.

Our findings demonstrate that fouling assemblages in marinas are structured by the interaction of factors rather than by single factors acting independently. The interactive effects of distance from the marina entrance and orientation highlight the role of the spatial configuration of marinas in shaping fouling assemblages, with implications for monitoring and the ecological design of artificial infrastructures.