Assessment of NRDA Funded Oyster Restoration in the Gulf of Mexico
September 2021 - September 2026
Across coastal areas of the U.S. Gulf of Mexico, the Deepwater Horizon oil spill resulted in significant ecological injury and over 8 billion USD directed to restoration activities. The eastern oyster (Crassostrea virginica), an organism valued as a commercial fishery and as an ecosystem engineer, was identified specifically as being negatively impacted (injured) by the event. Oyster restoration projects were implemented with regional goals of restoring oyster abundance, spawning stock, and population resilience. Measuring regional or large-scale ecosystem restoration outcomes challenges traditional project-specific monitoring and outcome reporting collected at local scales. We examined the outcomes of oyster restoration at the project-level and identify and discuss potential pathways to measure progress toward region-level goals. An estimated 15 km2 of oyster habitat was restored across 11 different estuaries with 62 individual reef footprints created, ranging in size from > 0.2 to 0.64 km2. Individual sites were distributed across the salinity gradient, and all reefs were subtidal. One-year post-restoration, mean total oyster density across all sites was 53.0 ± 60.7 ind m-2 of which 38.4 ± 42.2 ind m-2 were adult (> 25 mm shell height) oysters. Recent data available for all sites indicates reduced densities of total oysters (44.6 ± 70.9 ind m-2) and adult oysters (14.6 ± 21.6 ind m-2). These data provide insight into project specific results and outcomes, suggesting an overall enhancement in oyster abundance from restoration, but fall short of informing outcomes at the regional level that incorporate cumulative effects on adjacent and connected reef populations, or resiliency of the overall oyster resource. Inclusion of water quality and oyster resource data outside of specific restoration project areas remains necessary to assess the impact of these projects on regional oyster resource abundance and resilience. Developing outcome measures that incorporate cumulative and synergistic impacts of individual projects will require reconciliation and consideration of project-level planning and monitoring performance targets with broader spatial and temporal monitoring requirements.