An analysis of the spider assemblage structure and the presence of indicator species in the Flemish coastal dunes are presented. The analysis is based on data from more than 170 year-round pitfall sampling campaigns from the 1970s onwards. We were able to find indicator species for all identified habitats. The assemblages are determined by variation in vegetation structure (succession), atmospheric and soil humidity and the occurrence of both natural of anthropogenic disturbance. In the fragmented habitats (grasslands and grey dunes), a clear relationship was found between the mean habitat size and the stability of the assemblage composition. In moss dominated dunes and short grasslands total species numbers do not increase with patch size. Due to microhabitat variation and the possibility of attaining viable population sizes the total number of typical species is, however, higher in larger patches. In small patches, edge effects are more important and the number of observed species is enlarged by the intrusion of species from nearby habitats.