Effects of extreme freshwater events and perkinsus marinus on crassostrea virginica stress response

Estuarine salinity is one of the most important factors affecting oyster (Crassostrea virginica) growth and Perkinsus marinus disease characteristics. The combined effect of increased freshwater inflows and P. marinus infection on oyster physiology is important to understand for improving the predictions of oyster response to increasing climate variability. This study determined the effects of rapid declines in salinity, such as those oysters experience after a strong storm or flood, and P. marinus infection on the scope for growth of oysters from the Laguna Madre, a hypersaline estuarine system. Scope for growth was assessed by determining clearance rate, absorption efficiency, ammonia excretion rate, and oxygen consumption rate for oysters at six salinity treatments: 10, 15, 20, 25, 30, and 35. Salinity did not have a significant effect on clearance rate, absorption efficiency, or oxygen consumption rate, but did significantly affect the rate of ammonia excretion. Scope for growth ranged from 37.25 J hr-1 g dry weight-1 to 867.46 J hr-1 g dry weight-1, and demonstrated a decreasing trend from the lowest to highest salinity treatments, indicating reduced growth potential with increasing salinity. Perkinsus marinus infection intensity ranged from low to moderately heavy, but did not have a significant effect on oyster scope for growth. Oyster condition index increased with increasing salinity treatment, likely reflecting Laguna Madre oyster tolerance for high salinities. Regardless, oysters experiencing rapid reductions in salinity demonstrated increased physiological function compared to oysters that remained at the control salinity 35, indicating that the normally high salinities of the Laguna Madre may not present optimal conditions for oyster growth. Results of this study improve understanding of oyster response to rapid decreases in salinity conditions influenced by human and climate-driven changes.