Habitat mimics were used to investigate the role of coralline algal frond length in determining spatial patterns in diverse gastropod assemblages on a rocky shore near Sydney, Australia. Frond length represents the vertical scale component of habitat structure, which is rarely experimentally manipulated. Length of fronds did not explain differences between gastropod assemblages at different tidal heights or among patches of turf separated by tens of metres in mid-shore areas. In contrast, changes in frond length caused large differences in the structure of gastropod assemblages in low-shore areas. Contrary to previous studies, the total abundance and diversity of gastropods was greater in turf with short fronds than with long fronds. Possible mechanisms for this negative relationship are discussed. Overall, the vertical scale component of habitat structure can have strong effects on associated faunal assemblages, but the magnitude of these effects depend heavily on local environmental conditions (e.g. different tidal heights).