Ecological studies of diversity at different spatial scales are important for our understanding of community processes. Here the patterns in the invertebrate fauna associated with the turf-forming red alga, Corallina officinalis, with increasing tide pool depth and in pools of different surface area and at different tidal heights are presented for two similar shores in north Wales. Corallina turf supports a diverse assemblage of invertebrates achieving high densities of individuals which makes an important contribution to local biodiversity. Overall 123 different taxa were identified with the most dominant species being the polychaete Spirorbis corallinae and small individuals of the mussel Mytilus edulis. There are significant differences in the invertebrate assemblage at different depths in tide pools and higher diversity and richness at shallower depths nearer the edge of pools where the alga is shorter and more compact than at deeper depths. Pool size and tidal height were also clearly important in structuring the assemblage where there were significant differences in diversity, richness and assemblage pattern, although these differences were not consistent between shores. Some measures of habitat complexity, such as algal volume, correlate well with species richness, though occasionally diversity is negatively correlated with the number of holdfasts. Variations in physical conditions afforded by different depths and in tide pools of different size at different tidal heights at the scales measured clearly play an important role in structuring both the complexity of habitat and its associated assemblage