Abstract
Genomic and physiological responses in Gulf killifish (Fundulus grandis) in the northern Gulf of Mexico have confirmed oil exposure of resident marsh fish following the Macondo blowout in 2010. Using these same fish, we evaluated otolith microchemistry as a method for assessing oil exposure history. Laser-ablation inductively-coupled-plasma mass spectrometry was used to analyze the chemical composition of sagittal otoliths to assess whether a trace metal signature could be detected in the otoliths of F. grandis collected from a Macondo-oil impacted site in 2010, post-spill relative to pre-spill, as well as versus fish from areas not impacted by the spill. We found no evidence of increased concentrations of two elements associated with oil contamination (nickel and vanadium) in F. grandis otoliths regardless of Macondo oil exposure history. One potential explanation for this is that Macondo oil is relatively depleted of those metals compared to other crude oils globally. During and after the spill, however, elevated levels of barium, lead, and to a lesser degree, copper were detected in killifish otoliths at the oil-impacted collection site in coastal Louisiana. This may reflect oil contact or other environmental perturbations that occurred concomitant with oiling. For example, increases in barium in otoliths from oil-exposed fish followed (temporally) freshwater diversions in Louisiana in 2010. This implicates (but does not conclusively demonstrate) freshwater diversions from the Mississippi River (with previously recorded higher concentrations of lead and copper), designed to halt the ingress of oil, as a mechanism for elevated elemental uptake in otoliths of Louisiana marsh fishes. These results highlight the potentially complex and indirect effects of the Macondo oil spill and human responses to it on Gulf of Mexico ecosystems, and emphasize the need to consider the multiple stressors acting simultaneously on inshore fish communities.
Highlights
The Gulf of Mexico (GOM) is a highly dynamic and productive ecosystem that supports recreational and commercial fishing, tourism, as well as significant oil and gas exploration and extraction industries (~600 million barrels per year) [1,2]
Freshwater diversions in Louisiana which were increased in volume to slow the progression of oil into coastal habitats were evident at GT as revealed by the drop in salinity in June and August, which averaged 6 lower than the calculated 5 year mean (2008– 2013) for that time of the year
Two months following oiling, there was an observed increase in the concentrations of Cu, Ba, and Pb only in otoliths at the impacted site, which could indicate a signature of Deepwater Horizon Oil Spill (DHOS) oil or another distinction for fish from GT in environmental exposure to these elements
Summary
The Gulf of Mexico (GOM) is a highly dynamic and productive ecosystem that supports recreational and commercial fishing, tourism, as well as significant oil and gas exploration and extraction industries (~600 million barrels per year) [1,2]. On April 20, 2010, the explosion of the Deepwater Horizon drilling rig precipitated the 84-day release of an estimated 4.5 million barrels of Louisiana crude oil into the Gulf of Mexico [3]. The Gulf killifish (Fundulus grandis) has served as a valuable model species to assess oil-spill impacts. Fundulus spp. are numerically dominant marsh residents [17], serve as an important trophic link in estuarine food webs [18], exhibit considerable site fidelity [19,20], and perform well in laboratory trials without demonstrating handling artifacts on fitness [21]
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