Understanding community diversity on coastal defences : the role of key drivers and ecological enhancements

Coastal defences have become prevalent in the marine environment in response to rising sea levels and increasingly frequent coastal storms. However, due to insufficient habitat heterogeneity and physical complexity such structures support lower biodiversity than natural rocky shores. As a result, a range of ecological enhancements have been developed to address the diversity deficit. This thesis monitored colonization of an ecologically enhanced rock armour defence at Runswick Bay, North Yorkshire. Artificial rock pools and sandstone boulder habitats were incorporated into the defence design to increase habitat heterogeneity and groove microhabitats were engineered to increase small-scale complexity of granite boulders. Fourteen months after construction, diversity of sessile and mobile assemblages was significantly higher in artificial pool and sandstone boulder habitats than in unmodified granite boulder habitats. The community which developed on engineered grooves was not different to that of substrates without grooves. This thesis also examined whether fine-scale complexity (rugosity) and substrate orientation act as drivers of diversity on coastal defences. At both mid and upper shore height, the most rugose substrate had the highest diversity of sessile and mobile species. Over a regional scale, the age of defence was more important in determining community structure than rugosity. In addition, diversity and structure of communities differed significantly between North, North-east and East orientations at mid and upper shore height. This thesis demonstrates that increasing the habitat heterogeneity and incorporating natural substrata into rock armour defences can improve biodiversity. This thesis also demonstrates the importance of fine-scale complexity across tidal heights, and that environmental factors determined by orientation affect community structure. These results can be used to inform how ecological enhancements are applied in future developments