Examining the Sustainability of Restored Sub-Tidal Oyster Reefs in Coastal Louisiana

Climate related alterations and anthropogenic disturbance threaten the ecological integrity and sustainability of coastal estuaries. Many activities seek to restore and sustain these at-risk areas with the goal of restoring systems to historic patterns of succession and community development; however long-term monitoring of restoration projects remains limited. Additionally, restoration efforts aim to achieve certain success thresholds, however, these thresholds are often vague, absent, or inconsistent, and receive little long-term analyses following restoration. A key coastal engineer, the eastern oyster (Crassostrea virginica), provides multiple ecosystem services, but recent population decline has prompted investment in restoration. Restoration activities include cultch planting, reef enhancement, incorporation into living shorelines, and hatchery construction for oyster seed. This work examines restoration trajectories and project sustainability for two oyster restoration projects in coastal Louisiana. Here I quantify on-reef oyster density and demography, adjacent shoreline movement, and water filtration services for a living shoreline project in Sister Lake Louisiana 11 years post-construction (2009 – 2020), as well as examine the outcomes of oyster restoration projects implemented across Louisiana as part of the early restoration funding from the Deepwater Horizon Oil Spill. Restored reefs persisted through time but decreased in integrity and robustness 2-3 years post-restoration. Declines were likely influenced by sub-optimal water quality (i.e., salinity) and heavy localized harvest. Despite these declines, reefs still provided crucial ecosystem services (i.e., water filtration) to estuarine habitats. While success thresholds vary between restoration projects, I suggest restoration success thresholds may incorporate three different performance criteria (achievement of target densities; provision of ecosystem services; achievement of harvest quotas). For these criteria to be met and detected, incorporation of long-term monitoring and adaptative management are crucial. This work provides critical information for managers on the outcomes of oyster restoration projects and explains specific variables which influence project sustainability