To examine the effects of submergence time, free-space availability, and larval supply on height-related differences in settlement density of Semibalanus cariosus, we monitored the daily settlement density in plots where all benthos were removed daily and in natural-community plots, which were left undisturbed, at two sites with different tidal heights: the centre and the upper limit of S. cariosus zone, during one settlement season. Settlement density was higher at the low-tidal site, where settler mortality was low, than at the mid-tidal site, where settler mortality was high. The between-site differences in settlement was determined by larval preference for height and not immersion time. The settlement preference for height was masked on days with high larval supply, since suitable settlement sites in lower height were saturated by settlers.