Oyster castles: a 2,000-foot living wall to slow erosion in Laurel Bay, South Carolina

# What happened A series of interlocking concrete blocks called oyster castles are being stacked along the shoreline of Laurel Bay, South Carolina. When the project is finished next month, the wall will span about 2,000 feet. The Nature Conservancy led the effort with federal agency partners to protect homes and a nearby park that sit immediately next to Port Royal Sound.

# How oyster castles work Oyster castles are hollow, stackable blocks engineered to reduce wave energy and create habitat for oysters. Once placed, the blocks break and slow waves before they reach the shoreline. That reduced wave action allows suspended sediment to settle behind the wall and low marsh plants to reestablish.

Oysters then attach to the blocks and to one another. Over time the accumulated shell and oyster growth builds vertical relief. That natural accretion can raise the structure and help maintain protection as sea levels rise.

# Evidence on the ground Project partners report that at the oldest installed sections they have already seen measurable benefits: sediment has filled back in behind the wall, marsh grass has regrown, and many oysters have colonized the blocks. That local evidence is the main basis for moving forward with the full-length installation.

# Why this approach was chosen for Laurel Bay Laurel Bay is a residential community with many military families, located next to a Marine Corps base. Homes and a public park sit very close to the water. Local salt marshes and adjacent uplands had eroded over time, and climate-driven increases in water levels and storminess are expected to worsen erosion.

The oyster-castle method pairs immediate shoreline stabilization with ecological benefits: it reduces erosion while providing substrate for oysters and habitat for other coastal species. The living reef capacity means the structure can adapt biologically as conditions change, rather than relying on static hard infrastructure alone.

# Partners and timeline The Nature Conservancy collaborated with federal agencies on the project. Construction is ongoing and the wall is scheduled to be complete next month. Monitoring of older sections has already shown early signs of success.

# Practical implications for residents and managers

• Short term: the stacked wall reduces wave energy and should slow active erosion of the shoreline and adjacent properties.
• Medium term: trapped sediment and returning marsh vegetation can restore some natural defenses and help buffer flooding and storm surge.
• Long term: as oysters colonize and build shell, the structure has the potential to gain elevation biologically, which helps it remain effective as sea level rises.

# Considerations and next steps The reported benefits at older sections are promising, but the long-term performance depends on oyster recruitment, water quality, and ongoing monitoring and maintenance. If oysters do not persist or water conditions deteriorate, the reef-building process will be limited. Agencies and local stakeholders will need to track colonization, sediment accretion, and vegetation recovery to evaluate whether additional interventions are required.

# Bottom line The oyster-castle wall is a nature-based shoreline defense that aims to slow erosion, rebuild marsh, and provide habitat. Early results at existing sections show sediment and vegetation returning and active oyster colonization. The full 2,000-foot installation will test whether this living approach can protect Laurel Bay in the face of rising waters and increased storm activity.