Abstract
Oyster reefs are important ecosystems that provide invaluable services for coastal communities. Crassostrea virginica populations in the northern Gulf of Mexico have suffered heavy losses in the 21st century due to alterations in water quality from various disasters, including openings of the Bonnet Carré Spillway. These flooding events reduce salinity, increase nutrient and pollutant levels, and introduce freshwater harmful algal species into coastal waters where oysters live. Significant resources have been invested to restore oyster reefs, but recovery is reliant on the survival of early oyster life stages. We assessed the effects of stressors associated with flooding events on larval and juvenile oyster development to better understand the tolerances of early oyster life stages. We exposed D-stage larvae to a range of dissolved oxygen (1-8 mg/L O2), microcystin (0-20 μg/L), pH (7.1-8.1), and salinity (3-15 ppt) concentrations in 96-hour single stressor experiments. Larvae were not affected by any microcystin or pH concentrations tested, but low salinity and hypoxia reduced shell growth. Using concentrations informed by the results of the larval assays, we then exposed juvenile oysters to the same water quality stressors for 24 days in the lab. Juvenile wet weight and shell growth were decreased by hypoxia, low pH, and low salinity, but microcystin had no effect. These laboratory-exposed juveniles were then transplanted to the field to assess how prior exposure to stressors affects growth and survival in natural conditions. Larval and juvenile oyster survival was relatively unaffected for the duration and stressor concentrations tested, but the negative impact on growth of early life stages may limit the recovery and resilience of oyster reefs. Further research is needed to determine the combined impact of multiple stressors across all life stages of oysters, as the frequency and intensity of extreme flooding events rise.
