Triplicate samples of Corallina officinalis L. were collected from either side of 5 large mid-shore pools on 3 shores in north-eastern England (Ravenscar, Filey Brigg and Flamborough) in order to examine the patterns of variation in abundance of different ostracod species and in assemblage structure over a range of spatial scales. Three-way nested ANOVA showed that there was no significant difference in total ostracod abundance at any of the spatial scales examined. However, the 9 most abundant ostracod species showed different patterns of abundance at the different spatial scales. Only 3 species showed significant variation in abundance between shores; however, most of the variation was recorded at the between-pool, within-shore level. Seven species showed a significant variation in abundance between pools nested within shores (100 to 200 m scale), but not from within pools (5 to 10 m scale). Semicytherura nigrescens showed a significant variation in abundance at the km scale and within-pool level but not between pools, whereas Hirschmannia viridis showed a significant difference in abundance at 5 to 10 m scales, but not at the other scales. There was significant variability in species richness (i.e. number of species per quadrat) at the km scale, but not at the other scales. However, there was a significant variability in assemblage diversity (H') at the km scale and the 100 to 200 m scale, but not at the 5 to 10 m scale. H' and the number of species per quadrat were significantly higher at Filey Brigg than on the other 2 shores. An MDS plot generated from a Bray-Curtis similarity matrix showed that the Flamborough samples formed a discrete cluster, whereas there was some overlap between the Filey and Ravenscar samples. Two-way nested ANOSIM showed that there was a significant difference in assemblage similarity both between shores using pools as samples and between pools using shores as samples. SIMPER indicated that the absence of S. nigrescens and relative abundance of 2 other species accounted for most of the dissimilarity between Flamborough and the other 2 shores. There was a significant negative correlation between the percent similarity and the spatial distance between quadrat pairs. The current study showed that there was considerable variation in individual ostracod species abundance and in the assemblage composition at the 3 spatial scales and that overall assemblage similarity decreased with spatial distance between samples.