Hard substrates including animal body surfaces are valuable resources for sessile organisms. The shell of a marine intertidal mollusc Turbo (Lunella) coreensis is often colonized by a number of epibiotic organisms. Orientation preferences and potential competitive relations in these epibionts were investigated in the present study.

Algal species exhibited a strong preference for dorsal surfaces, being nearly absent on ventral surfaces. Sessile animals exhibited a strong preference for the peripheries of the aperture and, in contrast to algae, less common on the dorsal surfaces of Turbo.

Colonization by algae, especially of foliate forms, was restricted to the dorsal surfaces due perhaps to their need for sunlight and susceptibility to friction. Consideration was given to ecological background of these phenomena.