Ecological and Erosion Protection Functions of Chesapeake Bay Living Shorelines
Living shoreline habitat restoration activities are typically designed to control erosion, while simultaneously enhancing estuarine habitats. Expected outcomes are shoreline protection, estuarine habitat creation in the intertidal, beach and subaqueous zones, and enhanced habitat services for fauna and flora communities. To date, there has been limited research on the ecosystem functioning of living shorelines, particularly for living shoreline projects in higher energy systems that include rock structure, such as marsh-sills (low "free standing" stone structures placed near the marsh shoreline). Our recent research, funded by Chesapeake Bay Trust, NOAA Habitat Conservation and Maryland Department of the Environment, documented trade-offs involved in habitat conversion associated with various shoreline protection techniques (living shoreline, riprap revetment), which included relative increases in epifaunal suspension feeders on marsh sills.
Bilkovic, D. M., & Mitchell, M. M. (2013). Ecological tradeoffs of stabilized salt marshes as a shoreline protection strategy: Effects of artificial structures on macrobenthic assemblages. Ecological Engineering, 61, 469-481. (pdf)
Armoring shorelines to prevent erosion is a long-standing global practice
that has well-documentedadverse effects on coastal habitats and organisms. A relatively new form of shoreline protection, referredto as hybrid stabilization, incorporates created marsh in combination with a stabilizing structure such asa low-profile stone sill and is being implemented in many US coastal states as a means to not only con-trol erosion but also to restore coastal habitat. However, there has been limited scientific investigationof ecological benefits and impacts associated with implementation of hybrid stabilization. We evaluatedrelative habitat capacity of marsh-sills by comparing plant, sediment, and benthic macroinvertebrateattributes in intertidal and subtidal zones of existing marsh-sills, natural marshes, tidal flats, and ripraprevetment within two subestuaries of Chesapeake Bay, USA. Low and high marsh plant characteristics(stem count and height) of marsh-sills were similar to or greater than natural marshes. However, sedimentwas coarser, total organic carbon and total nitrogen concentrations were lower, and benthic macrofau-nal community structure differed in marsh-sills compared to natural marshes. Marsh-sills supportedlower deposit-feeding infaunal biomass than marshes in the intertidal. Epifaunal suspension-feederswere most prevalent at sites with artificial structure (riprap and marsh-sill), but highly variable amongsubestuaries. Infaunal abundance, biomass, diversity, and proportion of suspension/interface and depositfeeding animals were greater in shallow subtidal than in intertidal environments. Conversion of exist-ing habitat to marsh-sills may cause localized loss of benthic productivity and sediment bioturbationand nutrient-cycling functions, with the opportunity to enhance filtration capacity by epifaunal recruit-ment to structures. When creating marshes that require structural support, there should be a balance ofminimizing loss of existing habitats while encouraging use of suitable structural habitat for suspension-feeders. If properly implemented, the addition of structural habitat could subsidize secondary productivityparticularly in areas where loss of complex biogenic habitat (e.g., oyster reefs) has occurred.