Graduation Year


Document Type




Degree Name

Master of Science (M.S.)

Degree Granting Department

Marine Science

Major Professor

Ernst B. Peebles, Ph.D.

Committee Member

Steve Murawski, Ph.D.

Committee Member

Mark S. Peterson, Ph.D.

Committee Member

David Hollander, Ph.D.


Otolith, oil spill, increment width analysis, microchemistry


Oil from the Deepwater Horizon blowout reached the Gulf of Mexico coast in the summer of 2010 and potentially exposed species living in those areas to toxic chemicals. The purpose of this study is to examine otoliths from Red Drum (Sciaenops ocellatus) for evidence of oil exposure that could be related to reduced growth rates. Because otolith growth and somatic growth are directly related, differences in annulus measurements can indicate differences in annual somatic growth, which is a good indicator of overall fish condition, and translates into changes in survival and lifetime reproductive potential. This study assessed variation in otolith elemental composition in years before, during, and after the oil spill using laser-ablation inductively-coupled plasma mass spectrometry, with emphasis on trace metals previously found in MC252 oil. Relative annual growth rates were estimated by calculating mean increment measurements for each age, and calculating a percentile for each observation. Growth was then compared with otolith elemental profiles. These two analyses were used to investigate associations between any observed growth variation and the temporal profiles of oil-indicator and stress-indicator elements. Otoliths obtained from Florida archaeological sites were used as a baseline for pre-industrial elemental compositions. Fish taken from 12 sampling sites in Florida and Louisiana with varying degrees of oil intrusion were analyzed for otolith element composition. Individual measurements were classified using Similarity Profile Analysis (SIMPROF, Clarke et al. 2008) and resulting SIMPROF groups were plotted on a seriated heat map to visualize elemental abundance groups. The largest group with the lowest elemental abundances was used as a reference group. This group was compared to higher-element abundance groups and to fossil otoliths found in Native American middens on Weedon Island, FL using nonparametric multivariate analysis of variance (NP-MANOVA) and Canonical Analysis of Principal Coordinates (CAP) to determine similarities of modern fish groups and an ancient baseline. Growth rates were then compared to the microchemistry groups to determine if there are any correlations with growth rates and otolith trace metal compositions.

This study did not find any correlation between the Deepwater Horizon oil spill event and either Red Drum otolith microchemistry or growth. Otolith oil-metal concentrations did not vary significantly among study years, and there was no relationship between microchemistry and otolith-based growth rate. While there was decreased growth in 2010, the decreased growth appeared to be due to unusually cold winters during that year. Oil metal concentrations measured in the otoliths indicated continuous metal exposure rather than exposure to an episodic oil-spill event.

This study also verified the use of archaeological otoliths as a viable microchemical baseline for pre-industrial otoliths. Preserved otolith material had very low hydrocarbon-associated metal concentrations, which is expected in otoliths that were formed before the period of heavy anthropogenic influence on coastal waters. This study represents a novel effort to compare pre-industrial-age microchemistry to the microchemistry of fish collected from impacted areas following a large oil spill.