GEOHISTORICAL BASELINES OF BODY-SIZE DISTRIBUTIONS AS ECOLOGICAL INDICATORS OF OYSTER REEF RECOVERY FROM THE DEEPWATER HORIZON OIL SPILL

The near- and long-term ecological effects of the Deepwater Horizon oil spill in Louisiana are only just beginning to be assessed. We used time-averaged death assemblages of intertidal oysters (Crassostrea virginica) from multiple impacted and control sites to establish a pre-spill baseline of body size structure with which to assess the effects of the oil spill. This baseline was compared to post-spill body size data collected from live oysters in 2011, 2012, and 2013.

Body size is an important functional trait that can constrain metabolic and energy assimilation rates, thus influencing both future growth and reproduction, and is expected to vary along disturbance gradients according to ecological and energetic constraints. We therefore expected average body size of adult oysters (>65 mm shell length) from impacted areas to decrease due to increased stress related to direct and indirect impacts of the oil spill.

Body size data were analyzed using a Before-After-Control-Impact (BACI) design. Preliminary results indicate no significant interaction between time (before/after) and treatment (control/impact) factors (BACI contrast = 0.607, se = 3.4056, p = 0.8614), suggesting that average body size of adult oysters remained relatively unchanged after the oil spill. This result is not an indication that oysters were not exposed to (or consumed) oil-derived materials; rather they imply that oysters either recovered rapidly following the immediate impact of the spill, or simply that the oil spill’s impact on intertidal oyster beds was not severe enough to influence oyster population dynamics.