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

Eastern oysters support a critical commercial industry and provide many ecosystem services to coastal estuaries yet are currently threatened by changing estuarine conditions. A changing climate alongside river and coastal management strategies are affecting freshwater inflows into productive oyster areas, causing more frequent and extreme salinity exposure. Although oysters are tolerant to a wide range of salinity means and variation, more frequent and extreme exposure to low salinity (< 5) impacts oyster populations and aquaculture operations. This study assessed four Louisiana, USA oyster stocks to explore population-specific responses to low salinity exposure. Hatchery-produced progeny (< 25 mm) were deployed in baskets kept off-bottom on longline systems in a low salinity (mean ± 1 SEM daily salinity of 8.7 ± 0.2, ranging 1.2 – 19.0) and a moderate salinity (mean ± 1 SEM daily salinity of 16.8 ± 0.3, ranging 4.8 – 30.0) environment for one year with growth and mortality determined monthly. Significant differences in cumulative mortality between stocks at the end of the study were found at the low salinity site, with the greatest increase in cumulative mortality occurring mid-July to mid-August. Mortality differences between stocks suggest that discrete oyster populations may be better suited to low salinity or low salinity events than others. This difference may be attributed to similarity between site of origin and grow out site conditions and/or to greater salinity variability and therefore higher phenotypic plasticity in some oyster populations compared to others. The identification of oyster stocks able to survive under extreme low salinity conditions would facilitate the development of “low salinity tolerant” broodstock to support aquaculture in areas experiencing and predicted to experience low salinity events.