Abstract
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.
Highlights
Coastal and estuarine environments worldwide are under increasing pressure from a variety of human and environmental factors, including coastal urbanisation and climate change related impacts, such as sea level rise and increased storm events
Three species of barnacles were recorded at the sites surveyed, Semibalanus balanoides, Autrominius modestus and Chthamalus montagui, with Autrominius modestus the only non-native species recorded
At Blackness, Semibalanus balanoides and Autrominius modestus were recorded as Chthamalus montagui was out of its geographical range (Crisp et al, 1981)
Summary
Coastal and estuarine environments worldwide are under increasing pressure from a variety of human and environmental factors, including coastal urbanisation and climate change related impacts, such as sea level rise and increased storm events. Artificial structures are typically designed as plain-cast and lack the habitat structural complexity (hereafter complexity) associated with the geodiversity of natural rocky shores such as fine-scale (mm-cm) surface roughness, grooves (mm) and microhabitats (cm). Another key factor influencing the success of intertidal organisms, higher up in the tidal frame, is risk of desiccation (Cartwright and Williams, 2012), which is closely linked to microclimate. Ecological Engineering: X 1 (2019) 100002 the complexity of hard structures potentially influences the microclimate as well as the physical habitat available for intertidal species
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