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

Recognition of the global loss of subtidal oyster reefs has led to a rise in reef restoration efforts, including in the Gulf of Mexico. Reef restoration in the Gulf consists primarily of deploying hard substrate, and allowing oysters to recruit, grow, and proliferate, eventually building a living reef. Despite the large amount of resources devoted to the design and construction of oyster reefs, evaluation of the site prior to reef installation is often limited. Created reef success depends entirely on selecting a location that supports long-term oyster growth and survival, including the recruitment and survival of on-reef oysters. We examined oyster growth, mortality, condition and disease prevalence in different stocks of oysters located in protected cages, as well as oyster recruitment and mortality on experimental reef units in three different locations along the Louisiana Gulf coast in 2011 and 2012. Over a two-year period, our highest salinity site with the highest oyster growth rate in protected cages demonstrated the least likelihood for reef restoration success based on on-reef oyster population failure (high recruitment, 100% mortality). In contrast, our mid-salinity site with moderate oyster growth and on-reef recruitment had low and moderate recruitment and growth rates with low overall mortality, while the lowest salinity site exhibited extreme variability in all oyster responses on and off-reef due to one year of extended low salinity (< 2), and one year of above average salinity. The difference in oyster growth and survival rates between caged oysters and on-reef recruited oysters at each site clearly indicates that restoration suitability indices incorporating both oyster population dynamics and in-situ on-reef biotic and abiotic interactions are critical in better directing site selection for reef restoration efforts.