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

Understanding how different life history stages are impacted by extreme or stochastic environmental variation is critical for predicting and modeling organism population dynamics. This project examined recruitment, growth, and mortality of seed (25-75 mm) and market (> 75 mm) sized oysters along a salinity gradient over two years in Breton Sound, LA. In April 2010, management responses to the Deepwater Horizon oil spill resulted in extreme low salinity (< 5) at all sites through August 2010; in 2011, a 100-year flood event resulted in low salinity during springtime. Extended low salinity (< 5) during hot summer months (>250C) significantly and negatively impacted oyster recruitment, survival and growth in 2010, while extended low salinity (< 5) during spring months (< 250C) in 2011 had minimal impacts on oyster growth and mortality. In 2011, recruitment was limited which may be due to a combination of low spring time salinities and the high 2010 market-size mortality and minimal recruitment resulting in limited population of reproductive size oysters in 2011. In both 2010 and 2011, Perkinsus marinus infection prevalence remained low throughout the year at all sites and all infection intensities were light. Oyster plasma osmolality failed to match surrounding low salinity waters in 2010, while oysters appeared to osmoconform throughout 2011 indicating that the high mortality in 2010 may be due to extended valve closing and resulting starvation in response to the extreme low salinities per se, or the combination of low salinity during high temperatures (> 250C). With increasing management of our freshwater inputs to estuaries combined with predicted climate changes, understanding how more extreme events affect different life history stages is key to understanding variation in population demographics of commercially important species and predicting future populations.