Biomarkers reveal sea turtles remained in oiled areas following the Deepwater Horizon oil spill

Abstract

Assessments of large-scale disasters, such as the Deepwater Horizon oil spill, are problematic because while measurements of post-disturbance conditions are common, measurements of pre-disturbance baselines are only rarely available. Without adequate observations of pre-disaster organismal and environmental conditions, it is impossible to assess the impact of such catastrophes on animal populations and ecological communities. Here, we use long-term biological tissue records to provide pre-disaster data for a vulnerable marine organism. Keratin samples from the carapace of loggerhead sea turtles record the foraging history for up to 18 years, allowing us to evaluate the effect of the oil spill on sea turtle foraging patterns. Samples were collected from 76 satellite-tracked adult loggerheads in 2011 and 2012, approximately one to two years after the spill. Of the 10 individuals that foraged in areas exposed to surface oil, none demonstrated significant changes in foraging patterns post spill. The observed long-term fidelity to foraging sites indicates that loggerheads in the northern Gulf of Mexico likely remained in established foraging sites, regardless of the introduction of oil and chemical dispersants. More research is needed to address potential long-term health consequences to turtles in this region. Mobile marine organisms present challenges for researchers to monitor effects of environmental disasters, both spatially and temporally. We demonstrate that biological tissues can reveal long-term histories of animal behavior and provide critical pre-disaster baselines following an anthropogenic disturbance or natural disaster.

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

“…Our results differ from those of Vander Zanden et al (2016), who found no δ 13 C change in the scutes of loggerhead turtles that foraged in the oiled area after the spill; δ 13 C in the loggerheads was ca. -15 to -18 ‰ before and after the spill, which is similar to our pre-spill values for Lk (Fig.…”

“…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. In contrast to findings for loggerhead turtles (Vander Zanden et al 2016), our results indicate that the oil signature was transferred to Lk, as also reported for 2 species of mesopelagic GoM fishes (Quintana-Rizzo et al 2015). In the fish, a δ 13 C decrease in muscle samples collected 5 mo after the spill relative to pre-spill samples was attributed to the ingestion of oilcontaminated prey (Quintana-Rizzo et al 2015).…”

“…The δ 15 N values were similar (ca. 10 to 15 ‰) in both species and did not change over time (Vander Zanden et al 2016;Fig. 2).…”

“…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.…”

Are we working towards global research priorities for management and conservation of sea turtles?

“…Turtles tend to ex hibit high fidelity to oceanic and/or coastal foraging habitats (Goodman Hall et al 2015, Shimada et al 2016, Vander Zanden et al 2016, which, in some places, could be the result of adults and late-stage juveniles retaining high fidelity to known resources after drifting there as hatchlings (Hays et al 2010a. However, turtle behaviour is also more complex than previously hypothesized, with many exceptions to traditional life-history models.…”