Potential impacts of the 2010 Deepwater Horizon oil spill on subtidal oysters in the Gulf of Mexico

The explosion of the Deepwater Horizon (DWH) drilling platform initiated an unprecedented chain of environmental perturbations that threatened sensitive nearshore habitats in the northern Gulf of Mexico in 2010. Here, we examined subtidal oyster reef populations monitored by state resource agencies prior to and after the DWH incident in the spring-summer of 2010. Fishery-independent surveys were conducted in each of the following Gulf States using either diver-collected quadrat samples (Louisiana, Mississippi, Florida) or dredge surveys (Texas) at fixed sites to assess trends in oyster density of recently settled (spat), juvenile to young adult (seed), or adult (market) oysters. Compared to baseline values (average 2006-2009), the densities of spat, seed, and market oysters were extremely low in 2010, with little recovery in 2011 and 2012 in areas within the central portion of the northern Gulf of Mexico (eastern Louisiana-Mississippi). In contrast, densities of all oyster size classes in western Louisiana and Texas (outside the footprint of oil or freshwater release) and juvenile oysters in Apalachicola Bay, Florida, revealed no consistent pattern of change in 2010 compared to baseline levels in 2006-2009. Thus, major declines in oyster populations occurred within the northern Gulf of Mexico in summer 2010, and populations remained low through 2012. The spatial footprint of this decline is largely coincident with the oiling and freshwater diversion response activities associated with the DWH incident, although many potential confounding factors are also considered. Fisheries-independent datasets offer much-needed baseline data that can be used to assess potential impacts from disturbances.