Summary

1. Urbanization of coastal habitats is increasing worldwide. However, most man‐made structures are poor surrogates for the habitats they replace and can strongly impact the diversity and functioning of coastal habitats.
2. The value of coastal engineering can be enhanced by the provision of microhabitats that facilitate colonization by marine life. One step forward is moved in this research by combining species coexistence theory, resource patchiness and applied ecology in order to find ways that maximize the biological diversity of coastal defence structures.
3. Featureless areas of a seawall were modified by the addition of microhabitats (resource) that were distributed in different configurations of patchiness.
4. Gastropod diversity peaked at intermediate levels of microhabitat patchiness. This appeared to be driven by different patterns of resource use among species. Gastropods dispersed longer distances on unmodified seawalls than on natural rocky shores, but when microhabitats were added the dispersal decreased. The ability to find microhabitats differed among species.
5. Our results confirm that patchiness in microhabitat distribution affects biodiversity. The extent of microhabitat patchiness could potentially be tailored by coastal engineers to meet specific conservation priorities: increasing diversity versus increasing number of individuals.