Fundulus grandis Otolith Microchemistry as a Metric of Estuarine Discrimination and Oil Exposure

The Gulf killifish, Fundulus grandis, is a vital component of saltmarsh ecosystems and an indicator species for environmental impacts, because of strong site fidelity. Also, their otoliths can provide a record of environmental conditions because they are metabolically inert, grow continuously with the fish, and incorporate trace elements from the environment. We used laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to determine chemical composition differences in Gulf killifish otoliths across the northern Gulf of Mexico. Fish collections started in fall 2012 and continued through summer 2013. Concentrations of Mn, Sr, and Ba varied among sites and allowed for discrimination of fish between estuaries in Louisiana (elevated Ba concentrations) and the west side of Mobile Bay, Alabama (elevated Mn concentrations). However, elemental signatures of otoliths from Mississippi, Florida, and the east side of Alabama could not be discriminated from one another. Regional differences in otolith elemental signatures in Louisiana and west Alabama appear to provide unique chemical tags for these waters and, thus, may have utility for nursery habitat determination for species with estuarine-dependent juveniles. Otoliths of F. grandis that had been exposed to oil (either from the 2010 Deepwater Horizon oil spill or because of close proximity to an oil refinery) did not differ in elemental signature between paired oiled and non-oiled sites. Therefore, the otoliths did not contain trace metals associated with oil. Also, the relative condition of F. grandis did not differ between paired sites. The presence of F. grandis at all sites, the lack of effect of oiling on relative condition, and no signal of oil-related elements in the otoliths suggest minimal long-term impact of the Deepwater Horizon oil spill on F. grandis.