OYSTER SHELL BAGS
Loose oyster shell placement method has been replaced overtime with alternative methods to increase the success of oyster reef recruitment in different conditions . One of the improved alternatives involves filling bags with loose shells to place on marsh sediments . This alternative is preferred over placement of loose oyster shell because it reduces settling , scattering and siltation of the shell reef , which can impact successful recruitment of oyster larvae ( VIMS , b ). Additionally , placing the shell into bags creates a stable reef structure that can buffer incoming wave energy and facilitate the accumulation of fine sediment on the shoreward side of the reef . This technique is used in most coastal communities in the southeastern region . It is recommended at locations where successful oyster recruitment and growth can occur . In South Carolina , these conditions occur along marsh vegetated edges within the intertidal zone . Bags can also be placed alongside other living shoreline practices to provide additional protection , especially for protecting the seaward “ toe ” which can erode and reduce the success of certain practices .
OYSTER SHELL BAGS
Site Selection
Exposed soils in the intertidal zone at the midpoint between an eroding bank and the mean low water ( MLW ) line are suitable for placement of oyster shell bags . 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 . Shell bags do not perform well at sites with a high sink depth or where there are large amounts of sediment deposition . In some instances , sinkage can be countered by setting bags on wooden pallets . Steep banks , especially in areas with soft sediments and high concentrations of fine soil particles (< 70 % silt / clay and > 30 % sand ), increase the potential for individual shell bags dislodging or causing the entire structure to shift downslope ( SCDNR , 2019 ). Below is an overview of suitable conditions for the placement of oyster shell bags :
›››› Salinity > 15ppt
›››› Gradual marsh bank slopes < 16 %
›››› Firm sediments where sink depth < 4 inches
›››› Low sediment deposition
›››› Low to moderate wave action
Materials and Preparation
Current SCDNR regulations require clean , cured , and dried oyster shells as the only approved substrate for oyster shell bags . It is recommended to quarantine shells for a minimum of six months before they may be placed , especially for shells originating outside of South Carolina . Treating oyster shells in this matter avoids the spread of shellfish diseases and the introduction of invasive species into South Carolina waters ( SCDNR , 2019 ). Generally , oyster shell bag reefs are made of nontoxic , UV-stabilized mesh bags filled with a hard substrate , primarily oyster shell . SCDNR previously used Duronet mesh bag netting to make oyster shell bags , which can be purchased in 2,000-foot or 3,000-foott rolls . The length of an unfilled bag is 4 feet and can fit roughly two-thirds of a bushel ( five gallons ) of oyster shell . This results in oyster bags with a final dimension of approximately 24 inches long x 8 inches wide x 8 inches high .
While the use of nylon mesh bags is common , the use of non-plastic oyster bags made of organic materials is highly preferred . The use of non-plastic bags prevents contaminating coastal waters with plastic pollution following the breakdown of oyster bags over time .
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