Investigating the Effects of Site Characteristics and Installation Material Type on Intertidal Living Shoreline Performance in Coastal South Carolina, USA

Abstract The efficacy of experimental intertidal living shorelines to create new reef oyster habitat and protect salt marshes from erosion has generated substantial public interest in their adoption as a nature-based solution to address coastal habitat loss. There is, however, a high degree of variability in natural shoreline physical characteristics, which are important to consider in terms of the likelihood of living shorelines reducing erosion and associated habitat loss. In this study, multiple treatment types were installed and monitored for 6 years, including sites with shoreline types that were previously avoided for traditional habitat enhancement projects (e.g., steep banks, very fine substrate, high wave exposure). Fiber-based treatments performed poorly, becoming dislodged or deteriorating before the end of the study in all cases. Oyster-supporting treatments, which included bagged oyster shells and cement-coated wire reefs, were more resilient and resulted in the accretion of marsh habitat, in some cases on the order of several meters of lateral marsh expansion. The best-performing treatments were placed above the bottom 25% of the tidal frame, close to the marsh (< 3 m from the marsh edge), and on moderately steep bank slopes (> 0.15). Poorly performing or failed treatments were often located on shorelines that did not exhibit one or more of these characteristics. Some treatments experienced marsh erosion but at slower rates than the negative controls. These results indicate that site selection, placement, and installation material are critical factors in determining the effectiveness of living shorelines to protect marsh shorelines from erosion.