MANUFACTURED WIRE REEFS ( MWRs )
Oyster reefs can form on a variety of surfaces , including metal wire structures like abandoned crab traps . Research has shown recruitment of oysters can be accomplished by placing repurposed crab traps within the intertidal zone ( Johnson et al ., 2019 ). Recruitment of oysters on wire substrates can also be optimized in several ways . Cement coatings on the surface of wire substrates can facilitate recruitment and help retain their structural integrity to extend the life of their deployment . Customized manufactured wire reefs ( MWRs ) have also been created which increase the amount of surface area where oyster larvae attach . Over time , successful repurposed crab traps and MWRs produce oyster reefs which stabilize shorelines and provide habitats for local fisheries and wildlife . Generally , wire reef projects take 2-3 years to successfully recruit oysters . They are also more viable for large scale restoration projects and reduce negative impacts caused by sediments compared to shelled methods .
Site Selection
MANUFACTURED WIRE REEFS ( MWR )
Exposed soils in the intertidal zone between the mean low water line and the marsh platform are generally suitable for MWRs . Recruitment of oyster larvae requires water salinity to be above 15 ppt . Conditions below 15 ppt salinity should be avoided , including areas where freshwater is frequently introduced . Wire reef projects can be used in softer sediment environments where traditional restoration material would sink due to the weight . Placing weights within the structures should be considered in sites with more intense wave action and tidal influence . Below is an overview of suitable conditions for the placement of manufactured wire reefs :
›››› Salinity > 15ppt
›››› Steep marsh bank slopes up to 30 %
›››› All wave actions
›››› All sediment conditions
Materials and Preparation
MWRs are constructed from the same wire mesh and have the general shape typically used for the construction of recreational and commercial crab traps , but materials can be purchased individually . They are also much lighter than bagged shells and take less effort to install . MWRs are constructed using a galvanized wire mesh . An optional outer coating of vinyl with a thin layer of cement can be applied to the wire to serve as an attractive substrate for the settlement of larval oysters . A thinset tile mortar is a good option for this , as it adheres well to the wire mesh and is cost effective ( SCDNR , 2019 ). It is suggested that after applying a thin layer of the cement to the entire surface of the MWR , the MWR is left to cure for at least two weeks prior to use in the construction of a living shoreline .
Installation
MWRs are installed on the intertidal bank halfway between the waterward marsh edge and the mean low water ( MLW ) line to provide favorable conditions for oyster survival and productivity . To create more surface area for larval oyster recruitment , the optimal dimensions for constructing MWRs are 48 inches long x 24 inches wide x 18 inches high ( SCDNR , 2019 ). MWRs can be secured to the sediment using # 3 J-bar rebar which is placed into the sediment through the mesh of the reef at four points ( two on each side ), holding the wire structure in place on the bank .
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