The living shoreline approach as an alternative to shoreline hardening: Implications for the ecology and ecosystem service delivery of salt marshes
Ecosystems are modified by human activities globally, with degradation of coastal ecosystems occurring at unprecedented rates. The demand for coastal defense strategies against storms and sea-level rise (SLR) has increased with population growth and development along coastlines. Shoreline hardening, a common defense strategy that includes the use of seawalls and bulkheads, is resulting in a “coastal squeeze” on estuarine habitats. However, few studies have evaluated the extent and consequences of shoreline hardening on coastal ecosystems. In contrast to hardening, living shorelines, which range from vegetation plantings to offshore breakwaters (sills) and plantings, are deployed to restore/enhance ecosystem services. However, the effectiveness of living shorelines in sustaining/enhancing ecosystem services has not been evaluated. We determined the prevalence and impact of shoreline hardening on estuarine habitats by coalescing national datasets and relating factors such as population density and storminess to hardened shoreline (%) within U.S. coastal counties. We then quantified the effectiveness of shorelines consisting of (1) a sill with landward marsh (2) marsh alone, or (3) a bulkhead in providing habitat for fish and crustaceans (nekton). Finally, to determine the erosion protection capability during a storm, we surveyed shoreline damage and measured shoreline elevations pre- and post-Hurricane Irene.
Our analyses revealed that 22,842km of U.S. shoreline (14%) has been hardened, 66% of which is along the south-Atlantic and Gulf coasts. These coasts contain >50% of U.S. salt marshes and are also most vulnerable to SLR, storm events, and future development. Sills with planted marsh supported higher abundances and diversity of nekton than bulkheads and even marshes alone. The added structural complexity of sills likely provided nekton with more refuges from predation and greater opportunity to use available food resources than bulkheads. Erosion protection was also greater along shores with sills and marsh than bulkheaded shores during Hurricane Irene. In one NC region, 76% of bulkheads surveyed were damaged, while no damage to shorelines with sills was observed. Our results suggest that living shorelines may sustain fish habitat and reduce erosion better than traditional hardening.