The ecology and ecological enhancement of artificial coastal structures.

Abstract

Due to predicted sea level rise, increased storm frequency and coastal urbanisation, artificial coastal structures are proliferating worldwide. It is now vital to understand the impact that artificial structures are having on the marine environment and it is becoming increasingly necessary to incorporate ecologically enhanced designs into both new and existing coastal infrastructure. This thesis examines the communities associated with coastal artificial structures and trials ways in which we can improve the habitat provided for marine organisms. Firstly, the existing communities present on wooden and rock groynes within four regions along the south coast of England were surveyed and quantified and compared to natural rocky shores. The groynes were found to be less diverse than the natural rocky shores yet the wooden groynes supported a greater variety of species compared to the rock groynes. Secondly in order to assess the stability of individual populations, the variation in recruitment and mortality of the barnacle Semibalanus balanoides, and recruitment of the limpet Patella vulgata and the mussel Mytilus edulis were monitored on wooden and rock groynes within two regions and compared to natural rocky shores. High spatial variation in recruitment was observed, yet overall, communities on the groynes were comparably stable to those on the natural rocky shores. This thesis also investigates the impacts of artificial structures on surrounding mobile communities and their contribution into the food web. Baited Remote Underwater Video (BRUV) and Stable Isotope Analysis (SIA) were used to assess the distribution of mobile fauna around pleasure piers and to determine if the mobile fauna were using the pier as a feeding resource. The results showed a greater number of species in close proximity to the pier and the SIA found evidence of links between trophic levels of species collected on and around the piers. In order to assess the connectivity between populations, hydrodynamic and particle tracking models were used to determine the potential for artificial structures to act as stepping stones for the dispersal of native and non-native species. As the majority of artificial structures are known to lack biological diversity, this thesis explores how increasing the surface heterogeneity of rock armour using low cost enhancement options and improving water retention on seawalls by attaching artificial rock pools can improve diversity. The ecological enhancements attracted new species including mobile fauna which were previously absent and increased the overall diversity of the structures. To conclude the key findings are summarised and future work and management advice is outlined.