Assimilation of Oil-Derived Elements by Oysters Due to the Deepwater Horizon Oil Spill

Abstract

During and after the Deepwater Horizon Oil Spill (DWHOS), oysters (Crassostrea virginica) were exposed to oil and susceptible to incidental consumption of surface and subsurface oil materials. We determined the contribution of oil materials from the DWHOS to diet of oysters by comparing carbon (C) and nitrogen (N) stable isotope ratios in oyster shell to ratios in suspended particulate matter (SPM) and in fresh and weathered oil. Average δ(13)C and δ(15)N values in oyster shell (-21 ± 1‰ and 9-11‰, respectively) were consistent with consumption of naturally available SPM as opposed to values in oil (-27 ± 0.2‰, 1.6 ± 0.4‰). Stable isotope ratios in oyster adductor muscle were similar to shell for δ(15)N but not δ(13)C, suggesting either a recent shift in diet composition or differential assimilation of C between tissue types. We found no evidence of assimilation of oil-derived C and N and, therefore, no evidence of an oyster-based conduit to higher trophic levels. Trace elements in shell were inconclusive to corroborate oil exposure. These findings are not an indication that oysters were not exposed to oil; rather they imply oysters either did not consume oil-derived materials or consumed too little to be detectable compared to natural diet.

δ13C and δ15N in the endangered Kemp’s ridley sea turtle Lepidochelys kempii after the Deepwater Horizon oil spill

“…Loggerhead turtles also returned to the oiled area after the spill (Vander Zanden et al 2016), but there was no δ 13 C change indicative of oil exposure in the loggerheads. In contrast, the δ 13 C change from 2010 to 2011−12 in Lk is consistent with the incorporation and subsequent fractionation of C from the oil (δ 13 C = -27 ± 0.2‰; Carmichael et al 2012) via direct oil ingestion, inhalation, or dermal absorption, the consumption of oil-contaminated prey, or incorporation of oil C at lower levels of the food chain (Shigenaka 2003, Graham et al 2010 and not a change in foraging location. Other studies that have documented the incorporation of oil C into lower trophic levels and at different depths in the GoM also reported depleted C signatures (Graham et al 2010, Mitra et al 2012.…”

Geohistorical records indicate no impact of the Deepwater Horizon oil spill on oyster body size

“…Our findings of little impact of the DWH oil spill on intertidal oysters in Louisiana are consistent with other studies of oyster populations [9,50]. For instance, Carmichael et al .…”

“…For instance, Carmichael et al . [50] conducted experimental transplants of hatchery-reared oysters along the Mississippi–Alabama coastline, and found that oyster growth was not significantly affected by potential oil exposure. Also, in Barataria Bay and Breton Sound in Louisiana, La Peyre et al .…”

Concentrations of the Genotoxic Metals, Chromium and Nickel, in Whales, Tar Balls, Oil Slicks, and Released Oil from the Gulf of Mexico in the Immediate Aftermath of the Deepwater Horizon Oil Crisis: Is Genotoxic Metal Exposure Part of the Deepwater Horizon Legacy?

“…7−17 In contrast, minimal attention has been paid to the potential threat of carcinogenic metals that are known to be in crude oil. 18−22 Metals are known to accumulate in marine animal tissues after oil spills.…”