Mitigating Impacts of Natural Hazards on Fishery Ecosystems

The Use of Living Shorelines to Mitigate the Effects of Storm Events on Dauphin Island, Alabama, USA

LaDon Swann

doi: https://doi.org/10.47886/9781934874011.ch4

Abstract.—Gulf of Mexico marshes have been found to support more than 80 species of fish, 60 species of birds, and many reptile, mammal, and invertebrate species (Stout 1984). In addition to the ecological services provided by salt marshes, the 2005 hurricanes in the Gulf of Mexico raised public awareness of the ability of intertidal marshes to reduce personal property damage from storm surges. Since marshes can be destroyed through natural or anthropogenic processes, methods to protect these areas are being developed; one such method is the use of “living shorelines.” Living shorelines serve multiple roles by controlling erosion, maintaining natural coastal processes, and sustaining biodiversity through land-use management, soft armoring, or combinations of soft and semihard armoring techniques. Living shorelines provide a viable alternative to common hardened structures such as bulkheads, stone revetments, and seawalls. One type of living shoreline was used at Saw Grass Point Salt Marsh on Dauphin Island, Alabama. Dauphin Island’s Fort Gaines Harbor was constructed in the 1950s by removing approximately 3 ha from Saw Grass Point Salt Marsh. The harbor now serves as one of Dauphin Island’s two primary access points for recreational and commercial boats to the Gulf of Mexico. Chronic erosion has resulted in the loss of 0.5 ha of the remaining marsh. This saline tidal marsh is of significant ecological importance and is one of only two on Dauphin Island. In 2004, a community-based restoration grant was used to protect and restore the marsh through the use of exposed nearshore precast concrete breakwaters called Coastal Havens. These structures function as detached breakwaters to minimize the effect of storm surge and boat wake through wave attenuation; they also provide suitable substrate for oyster colonization. These structures were selected over other erosion control technologies, including vertical bulkheads, rock or wooden sills, and headlands. In April 2005, 182 units were installed in two interlocking rows parallel to the east perimeter of the marsh in water approximately 1.3 m deep. Oyster density on the coastal havens, measured 19 months postinstallation, was 205 oysters/m2. Measurements behind the breakwater indicate some sediment accretion. The project cost was approximately US$335/m to protect 162 m of shoreline. The dual function of these structures has controlled the erosion behind the breakwater and has provided habitat for a wide array of National Oceanic and Atmospheric Administration trust resources, including locally important species such as spotted seatrout (also known as speckled trout) Cynoscion nebulosus, blue crabs Callinectes sapidus and Gulf stone crabs Menippe adina, eastern oyster Crassostrea virginica, red drum Sciaenops ocellatus, southern flounder Paralichthys lethostigma, and various species of commercially important shrimp (brown shrimp Farfantepenaeus aztecus, pink shrimp F. duorarum, and white shrimp Litopenaeus setiferus).