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

Limited empirical data exist on Crassostrea virginica physiological rates across the range of salinities and temperatures that populations are regularly exposed. This lack of data reduces the accuracy of growth and production models under changing environmental conditions. The objectives of this study were to quantify the clearance and oxygen consumption rates of C. virginica from Louisiana across a range of salinities (3, 6, 9, 15 and 25) and seasonal temperatures (17 ºC in winter, 27º C in summer) typical of the region. Salinity and temperature affected C. virginica physiology differently; salinity impacted clearance rates with reduced feeding rates at low salinities, while temperature had a strong effect on respiration rates. Highest clearance rates were found at salinities ranging between 9 and 25, with reductions ranging from 50-80% and 90-95% at salinities of 6 and 3, respectively. Oxygen consumption rates in summer increased fourfold compared to winter. Oxygen consumption rates were within a narrow range and similar between salinities in winter but showed significant variation between individuals and salinities in summer that likely reflected varying stages of gonad development. Valve movements measured at the five salinities indicated oysters remained opened between 50 and 60% of the time in the 6 to 25 salinity range and about 30% at a salinity of 3. Reduced opening periods, concomitant with narrower gap amplitudes, support the finding of limited feeding at the lowest salinity (3). These data indicate the need for increased focus on experimental determination of optimal ranges and thresholds to better quantify oyster population responses to environmental changes.