Marine fouling is a commercially important problem affecting abiotic and biotic surfaces. In this study we investigated the surface fouling on a colonial reef-building invertebrate, the bryozoan Pentapora fascialis, from the Welsh coast. We captured 300 scanning electron microscope (SEM) images of 5 colonies of the bryozoan P. fascialis in order to quantify the level of fouling on the exterior surfaces. Evidence for differential fouling was found to occur at several spatial scales, including between older and newer zooids, between proximal and distal regions of the same zooids and between colonies. The current year's growing zooids were found to have a higher level of fouling than older zooids. The difference in the mean level of fouling of proximal regions of zooids compared to distal regions was found to be significant in P. fascialis. In agreement with the differential fouling previously observed by other authors in the laminar bryozoan Flustra foliacea where the proximal region of a zooid was observed to have a higher level of fouling, the fouling coverage in P. fascialis was higher in the proximal region of zooids. A reduction of fouling on some bryozoan surfaces may be caused by production of antimicrobial compounds. Further studies of microbial fouling of a similar quantitative scale in other bryozoans could aid in the identification of novel antimicrobial agents useful for preventing microbial fouling on abiotic surfaces in the marine environment.