Maximising the ecological value of hard coastal structures using textured formliners

In order to enhance the ecological value of vertical hard coastal structures, hybrid designs with complex surface textures (such as a combination of grooves and pits) have been recommended. This strategy optimises ecological colonisation at two spatial scales: 1) at the mm-scale for barnacle abundance (shown to have bioprotective capabilities), and 2) at the cm-scale for species richness and abundance through the incorporation/creation of habitat features. To determine the optimal design for improving the intertidal habitat quality of vertical coastal defence structures, we conducted an ecological enhancement trial involving 160 artificial concrete tiles of different designs (and thus topographic complexity) and 24 cleared natural surfaces (150 × 150 mm) at three sites in the UK. Within 18 months, tile designs with intermediate levels of complexity (mm-scale surface roughness) were optimal in increasing barnacle cover compared to plain-cast tiles. Tiles with high complexity (with microhabitat recesses up to 30 mm deep) developed greatest species richness and mobile species abundance and had lowest peak air temperatures and highest humidity. Such textured ecological enhancements can help improve the habitat value of existing and future hard coastal structures by favouring the conservation of intertidal species in urban marine habitats and enhancing otherwise weak or absent ecosystem service provision.