Cooperative Fish and Wildlife Research Units Program: Louisiana
Education, Research and Technical Assistance for Managing Our Natural Resources

Restoration of oyster habitat across Louisiana may offer a valuable approach to mitigating anthropogenic nutrient inputs to coastal estuaries. The eastern oyster (Crassostrea virginica) and the reefs they create provide significant ecosystem services, including potential nutrient mitigation via bioassimilation, burial, and oyster-mediated denitrification. This study measured bioassimilation, burial, and oyster-mediated sediment denitrification in near-shore shallow-water (< 1 m water depth) and deep-water (> 1 m water depth) oyster reefs in Louisiana. Carbon (C) and nitrogen (N) in shell and tissue was within the range of previous studies, but was found to be influenced by reproductive status, size, and habitat type. Changes in tissue percent N and C post spawning combined with significant reductions in tissue weight from the release of gametes, resulted in 20 and 46% reduction in tissue N and tissue C load (mg) for a 100 mm oyster, respectively. Percent N and C buried in sediments were highest at shallow-water reefs (0.52  0.05% and 8.92  0.89% respectively), likely due to their close proximity to the marsh edge and thus exposure to a greater influx of detrital material. Closed-system ex-situ incubations indicated net denitrification in all habitat types studied, with the highest rates exceeding 600 µmol m-2 hr-1 during the summer, but no enhancement attributable to oyster reefs specifically. Considering the large extent of reefs and oyster production across coastal Louisiana, oyster habitats may still contribute to nutrient mitigation, but their unique contribution likely comes from bioassimilation, and removal of tissue and or shell from the system. Efforts to predict oyster reef nutrient mitigation requires incorporating timing of harvest and habitat context.