Marine and terrestrial communities are often hierarchically structured by one or more foundation species, which provide habitats for many other taxa. Interactions between coexisting habitat modifiers may have strong effects on patterns and processes in the dependent assemblage. Yet they are rarely studied, especially at a small scale. Small epibenthic patches co-dominated by barnacles Balanus crenatus Brugiere and several species of solitary ascidians in the White Sea soft bottoms support many dependent species. Barnacles occupy bivalve shells, small stones and conspecifics. Ascidian clumps develop on barnacles and their empty shells. Previous observations suggest that at the patch scale ascidians may replace barnacles over several years likely because of the negative interactions between them. Barnacles have distinct annual growth rings on their shells, which we used to trace their growth and survival in the field. No difference between the patches with different dominants would evidence no pronounced negati