Globally, shoreline protection approaches are evolving towards the incorporation of natural and nature-based features (living shorelines henceforth) as a preferred alternative to shoreline armoring. Emerging research suggests that living shorelines may be a viable approach to conserving coastal habitats (marshes, beaches, shallows, seagrasses) along eroding shorelines. Living shorelines typically involve the use of coastal habitats, such as wetlands, that have a natural capacity to stabilize the shore, restore or conserve habitat, and maintain coastal processes. They provide stability while still being dynamic components of the ecosystem, but due to their dynamic nature, careful designs and some maintenance will be required if habitat conservation is a goal. Living shorelines may represent a singular opportunity for habitat conservation in urban and developing estuaries because of their value to society as a shoreline protection approach and resilience to sea level rise. However, enhanced public acceptance and coordination among regulatory and advisory authorities will be essential to expand their use. To fully understand their significance as habitat conservation strategies, systematic and standardized monitoring at both regional and national scales is vital to evaluate the evolution, persistence, and maximum achievable functionality (e.g., ecosystem service provision) of living shoreline habitats.

Salt marsh ecosystems have declined globally and are increasingly threatened by erosion, sea level rise, and urban development. These highly productive, physically demanding ecosystems are populated by core species groups that often have strong trophic interactions with implications for ecosystem function and service provision. Positive interactions occur between ribbed mussels (Geukensia demissa) and cordgrass (Spartina alterniflora). Mussels transfer particulate nitrogen from the water column to the marsh sediments, which stimulates cordgrass growth, and cordgrass provides predator and/or heat stress refuge for mussels. Here, we test mussel facilitation of two functions in salt marshes that relate to N removal: microbial denitrification and water filtration. Microcosm experiments revealed that the highest rates of N₂ production and nitrification occurred when mussels were present with marsh vegetation, suggesting that mussels enhanced coupling of the nitrification–denitrification. Surveys spanning the York River Estuary, Chesapeake Bay, showed that the highest densities of mussels occurred in the first meter for all marsh types with mainstem fringing (1207 ± 265 mussels/m²) being the most densely populated. The mussel population was estimated to be ~197 million animals with a water filtration potential of 90–135 million L/hr. Erosion simulation models demonstrated that suitable marsh habitat for ribbed mussels along the York River Estuary would be reduced by 11.8% after 50 years. This reduction in mussel habitat resulted in a projected 15% reduction in ribbed mussel abundance and filtration capacity. Denitrification potential was reduced in conjunction with projected marsh loss (35,536 m²) by 205 g N/hr, a 16% reduction. Because of the predominant occurrence of ribbed mussels at the marsh seaward edge and because the highest proportional loss will occur for fringing marshes (20%), shoreline management practices that restore or create fringing marsh may help offset these projected losses.

Introduction: Marshes contribute to habitat and water quality in estuaries and coastal bays. Their importance to continued ecosystem functioning has led to concerns about their persistence. Outcomes: Concurrent with sea-level rise, marshes are eroding and appear to be disappearing through ponding in their interior; in addition, in many places, they are being replaced with shoreline stabilization structures. We examined the changes in marsh extent over the past 40 years within a subestuary of Chesapeake Bay, the largest estuary in the United States, to better understand the effects of sea-level rise and human pressure on marsh coverage. Discussion: Approximately 30 years ago, an inventory of York River estuary marshes documented the historic extent of marshes. Marshes were resurveyed in 2010 to examine shifts in tidal marsh extent and distribution. Marsh change varied spatially along the estuary, with watershed changes between a 32% loss and an 11% gain in marsh area. Loss of marsh was apparent in high energy sections of the estuary while there was marsh gain in the upper/riverine section of the estuary and where forested hummocks on marsh islands have become inundated. Marshes showed little change in the small tributary creeks, except in the creeks dominated by fringing marshes and high shoreline development. Conclusions: Differential resilience to sea-level rise and spatial variations in erosion, sediment supply, and human development have resulted in spatially variable changes in specific marsh extents and are predicted to lead to a redistribution of marshes along the estuarine gradient, with consequences for their unique communities.

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