Oyster Restoration Techniques

This content is excerpted from the GEMS Phase I Report: Oyster Reef Restoration.

Oyster reef restoration techniques vary in the process and materials used, environmental conditions required, social and legal contexts, and expected outcomes (shoreline stabilization, oyster harvest, water quality improvement, etc.). Six different oyster reef restoration techniques are widely used across the Gulf of Mexico, but which techniques are used varies by estuary (or locally). The expected outcomes vary by restoration technique.

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Structurally simple, subtidal, intensively harvested

This technique consists of placing cultch material (usually oyster shells, relic shells, crushed limestone, or crushed concrete), either loose or contained, so that the resulting structure lies flat along the estuary/ocean floor. This technique has been widely used throughout the Gulf for the primary purpose of providing oysters for harvest.

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Structurally complex, subtidal, intensively harvested

Large, durable structures (e.g. oyster balls, precast concrete structures, and limestone structures) are placed in subtidal areas to create substrate to which oysters can attach. The resulting oyster reef has a significant vertical component, provides a more complex structure which oysters (of varying ages) and other aquatic organisms can use for habitat, and is less likely to be buried by sediment or degraded by waves than the simpler structures in the previous technique.

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Structurally complex, subtidal, not intensively harvested

This technique is identical to the previous one, except that intensive harvesting (dredging or intensive tonging) is not permitted.

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Structurally complex, intertidal, not intensively harvested

Large, durable structures (e.g.oyster balls, precast concrete structures, rocks, limestone structures) are placed in intertidal areas to create substrate to which oysters can attach. Projects using this technique are often called “living shoreline” projects, as they are intended to protect shorelines from erosion by stabilizing sediment and attenuating waves as they approach the shoreline.

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Protection or enhancement of existing oyster reef

These projects focus on the protection of an existing oyster reef from intensive harvest (dredging), with or without reef enhancement (via seeding or placing oysters in existing reef area). Protected reefs could still allow low-impact harvesting methods (tonging or hand collection) that do not threaten the reef structure or long-term viability of the oyster populations. The objective of these projects is to support a sustainable oyster population, allow the reef to develop structurally over a long period, and possibly to create a source of oyster larvae to nearby reefs.

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Aquaculture: intertidal or subtidal, intensively harvested

Oyster aquaculture projects of varying methods, including all bottom and off-bottom techniques. These projects encompass both intertidal and subtidal projects, and are considered to be intensively harvested, since the primary goal of oyster farming is harvest and consumption.

Oyster reef restoration techniques used in each focal estuary as of 2018: 

  Simple subtidal, intensively harvested Complex subtidal, intensively harvested Complex subtidal, NOT intensively harvested Complex intertidal, NOT intensively harvested Protection and enhancement of existing reef Oyster aquaculture
Charlotte Harbor, FL     X X X  
Back Bay of Biloxi, MS     X X X  
Mobile Bay, AL X X X X X X
Galveston Bay, TX X X X X X  
Chandeleur & Breton Sounds, LA X     X    

Charlotte Harbor, FL: Because there is currently no oyster harvesting allowed in this estuary due to human health concerns linked to water quality, the techniques that include intensive harvesting, including aquaculture, are not implemented here. In general, projects in this area tend to be small and done in intertidal areas (for protection of adjacent habitat types). There is institutional resistance to subtidal projects because they are more expensive than intertidal ones, and harvest restrictions due to water quality issues limit the benefits of many subtidal projects.

Back Bay of Biloxi, MS: Commercial harvest of any type is prohibited in this estuary by state law, and recreational oyster harvest is not currently allowed due to health concerns, so the restoration techniques involving intensive harvest or aquaculture are not implemented in Back Bay of Biloxi.

Mobile Bay, AL: All six of the techniques could be implemented in this estuary. Placing simple substrate in subtidal areas with intensive harvest and placing complex substrate in intertidal areas without intensive harvest are the most common. There are some complex substrate, subtidal projects planned. Oyster farming and aquaculture activity is growing in the area and is a source of local pride and identity.

Galveston Bay, TX: All of the restoration techniques except aquaculture are currently implemented in this estuary. Placing simple substrate in intensively harvested subtidal areas is most common and is done in both public oyster areas and on private leases (by the leaseholders). The Galveston Bay Foundation does many intertidal shoreline protection projects aimed at protecting other habitats (e.g. marsh). There are some complex substrate subtidal projects aimed at promoting ecosystem services, but there is always pressure to open projects to harvest. About one-third of the bay is closed to harvest due to water quality issues, and some small, ecologically sensitive areas, such as Christmas Bay, have been recently closed to intensive harvest. While oyster aquaculture is not currently used here, it is being discussed as a potential future option to reduce harvest pressure on oyster reefs.

Chandeleur & Breton Sounds, LA: The only oyster restoration techniques used here are placing simple substrate in intensively harvested subtidal areas and three-dimensional, intertidal ‘living shoreline’ projects. The state uses simple, two-dimensional substrate to provide harvestable oysters, and the intertidal (shoreline or habitat protection) projects are done by organizations like The Nature Conservancy and the Coalition to Restore Coastal Louisiana. There have been a few very small demonstration projects placing complex substrate in subtidal areas, but these are unlikely to be scaled up because there is no large-scale oyster reef restoration of this type included in the Louisiana Coastal Protection and Restoration Authority master plan. There are no protected oyster reefs in this area, and there is currently no aquaculture, although there are ongoing efforts to obtain funding for it.

 

Image credits:
1. U.S. Navy photo by Mass Communication Specialist Seaman Scott Pittman/Released
2/3. Wikimedia Commons/Siim1234567
3. Florida Sea Grant
5. Robert Kerton