Populations of Caryophyllia smithii were studied at three sites of differing sedimentation regime in Lough Hyne, Ireland. The height, length, width and density of individuals were measured along with the depth of accumulated sediment on the rock substratum at each site. Calyx size was largest at the site of least sedimentation and smallest at the site of most sedimentation. In contrast, height of individuals was greatest at the site of most sedimentation and smallest at the site of least sedimentation. The height of individuals was correlated with the level of surrounding sediment (Pearson's correlation 0.836 P<0.05). The uppermost limit of C. smithii corresponded with the downward limit of the infralittoral zone at each site; 15, 13, and 12 m at the low, mid and highly sedimented site respectively. Density averaged over depth was greatest (70 ind m−2) at the site of moderate sedimentation and lowest (13 ind m−2) at the site of least sedimentation. Density was also found to increase with depth at the sites of moderate and high sedimentation.