While the majority of people on Earth live in cities, the majority (60%) of the world’s largest cities are located within 100 kilometers of a coast. The pollution and urban infrastructure (such as marinas, sea walls, or oil/gas platforms) emanating from cities greatly stresses coastal marine habitats. Coastal infrastructure tends to be vertical and smooth, offering little or nothing in the way of habitat niches or physical protection for various marine organisms. An eco-engineering approach to improve habitat quality and increase biodiversity is the addition of textural features, such as ledges, small holes, basins or crevices to the hard surfaces of urban marine infrastructure.
As predicted, overall microhabitat-enhancing interventions had a positive effect on the abundance and number of species across the studies. Nevertheless, the magnitude of their effects varied considerably, from zero to highly positive according to the type of intervention, the target taxa, and tidal elevation [Strain 2017: 434].
In the intertidal, interventions that provided moisture and shade had the greatest effect on the richness of sessile and mobile organisms, while water-retaining features had the greatest effect on the richness of fish. In contrast, in the subtidal, small-scale depressions which provide refuge to new recruits from predators and other environmental stressors such as waves, had higher abundances of sessile organisms while elevated structures had higher numbers and abundances of fish. The taxa that responded most positively to eco-engineering in the intertidal were those whose body size most closely matched the dimensions of the resulting intervention [Strain 2017: 426].
Strain, Elisabeth, et al., 2017, Eco- engineering urban infrastructure for marine and coastal biodiversity: Which interventions have the greatest ecological benefit?, Journal of Applied Ecology 55, https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2664.12961.
 The intertidal refers to the area between the low and high tide marks.
 Attached in place.
 Shallow area below/beyond the low-tide mark.