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The size and scope of oyster reef restoration projects, and the techniques used to implement them, are dictated by the goals of the project. Some of the major goals of a restoration project are to:
- Augment commercial harvest
- Serve as habitat.
- Improve water quality.
- Increase or improve spat set in an area by creating oyster sanctuaries.
- Maintain or increase biodiversity.
- Restore ecological function.
- Provide a barrier to prevent beach or shoreline erosion.
- Protect and enhance sea grass restoration projects.
Factors to Consider During Project Planning for Oyster restoration Projects
Restoration efforts should include initial consideration of basic factors such as suitable substrate (hard enough to support cultch material—substances which serve as places of attachment for oyster larvae), remains of previous oyster reefs, adequate spat set, fouling organisms, currents, predation rates, disease prevalence and intensity, salinity ranges, siltation rate, and tidal elevation. Some phytoplankton surveys might also help ascertain if enough food is available for the oysters. The success of the project will depend on selecting sites with the proper attributes to allow oysters to survive and flourish. The amount of cultch material needed is directly related to the softness of the bottom, so this factor is extremely important.
Once a suitable site is found several techniques can be used to restore oyster reefs, but they all depend on a reliable source of cultch material. The best material is oyster shell, but other substances have been used with varying degrees of success, including broken porcelain bathroom fixtures, clam shells, limestone marl, "reef balls," and even fly ash conglomerate (a by-product of coal-burning power plants). Oyster shell is often unavailable or too expensive to purchase, so some restoration projects involve the collection and recycling of oyster shells, like the SCORE Program does in South Carolina.
Provided that an adequate amount of cultch material is available, several techniques for restoring or rehabilitating reefs may be used.
Planting shell: In areas where recruitment is fairly predictable, large amounts of shell or other kinds of cultch material can be distributed for attachment of oyster larvae. The exact dimensions and alignment of the shells should be guided by results from initial surveys regarding substrate type, currents, and other factors. Very large projects may also require the placement of such materials as limestone or rock to serve as a base for the reef, especially in areas with heavy wave action. In some cases, shell is placed in mesh or wire bags and positioned in rows in the intertidal area to provide attachment substrate for oyster larvae. As the oysters begin to grow, other organisms may also accumulate, providing the basis for an oyster reef community.
Hatchery production of spat: If spatfall is historically low in an area it may be necessary to rely on an oyster hatchery to produce the required amount of spat. In this case the cultch material is usually placed inside mesh bags and immersed in tanks of mature oyster larvae that are ready to set. After larvae have attached themselves the bags are suspended from docks or rafts for a few weeks to allow the spat to grow or individual shells are put into floats to allow for more growth (called "oyster gardening") before they are placed on the restored reef. The SPAT program on Long Island, NY is an example of this technique.
Relocation of seed oysters: Another alternative in some states, like Louisiana, is to obtain seed oysters from areas known to produce large amounts of seed oysters and transport them on barges to areas where they can grow to establish new reefs. Depending on the hardness of the bottom, shell or other material may be needed on-site before the seed oysters are placed.
Examples of oyster reef restoration techniques
- Quickly distributing large amounts of shell with high pressure hoses to provide cultch for oysters. This technique work in areas that have known, reliable spat set.
- Constructing a linear reef of shell and rock to stabilize the shoreline while protecting sea grass plantings behind the reef. The grass plantings also enhance shoreline stability and provide additional habitat for organisms.
- Collecting and bagging oyster shell for use as cultch for spat set. Serving as habitat for oysters and other associated organisms, these bags of oyster shell will help establish new oyster reefs in intertidal areas.
- Using a hatchery to provide seed oysters in areas where spat set is nonexistent or unreliable. This will establish new reefs and improve water quality in the local area.