2 ± 0.4‰ (8) for barnacles collected in Breton Sound in 2010. In particular, the Barataria 2010 collection did not show the expected shifts towards larger 13ɛ values indicative of strong oil incorporation nor the hypothesized stronger oil signals and larger 13ɛ values towards the mouth of the estuary ( Fig. 3). Overall, 13ɛ results for both mussels

and barnacles showed no significant (P > 0.05, unpaired t test) negative shifts towards larger 13ɛ values calculated for use of the −27‰ value measured by Graham et al. (2010) for oil from Deepwater Horizon ( Fig. 2 and Fig. 3). Average shifts BIBF 1120 nmr were close to zero (+0.5 to +0.1‰ for barnacles and +1.0 to −0.3‰ for mussels), compared to larger 1–4‰ shifts measured previously for plankton samples affected by the Deepwater Horizon oil spill ( Graham et al., 2010). Forskolin clinical trial Sensitivity analyses

indicated that consistent shifts of at least 0.5–1.0‰ and at least 10–30% incorporation of oil would be necessary before a significant result of detectable oil would be achieved with the δ13C analyses of barnacles or mussels. Based on the δ13C results, selected samples were analyzed further for the more sensitive radiocarbon tracer. The radiocarbon results confirmed low use of oil by the filter feeders, with maximum uptake calculated for paired mussel samples as <1% (Table 1). All the various barnacle tissue and shell samples from control and potential oil impact areas had nearly identical Δ14C results and showed no geographic trends (Fig. 4). We did not detect any size-related Δ14C variation for mussels. The overall average for filter feeder use of oil from the Δ14C results was slightly above zero at 0.4 ± 0.3% (Table 1; mean ± 95% confidence level). Although stranded oil locally coated some marshes in Terrebonne and Barataria Bays, bay-wide respiration rates measured in this study did not show a strong enhancement Amylase associated with the oil. Measured respiration rates were within the central median range

of respiration rates observed in unpolluted estuarine waters (Hopkinson and Smith, 2005). Higher respiration rates in Breton Sound may be due to enhanced productivity in that system, which is fertilized by inputs of nutrient-rich Mississippi River water from the Caernarvon diversion (Day et al., 2009). Respiration results were not consistent with ideas of large-scale submarine deposition of oil and subsequent high summertime metabolism of this oil in well-mixed estuaries. Nonetheless, metabolic contributions of 10–30% for oil would not be ruled out by the respiration measurements, making results from isotope analyses of filter feeding barnacles and mussels important additional data for in tracking the fate of oil in these food webs. It was surprising that so little oil (<1%) entered estuarine food webs, but there are several possible factors that could combine to explain the lack of oil incorporation.