Comparison of Otolith-Based Growth Rates and Microchemistry in Red Drum Before, During, and After the Deepwater Horizon Oil Spill

• Main Author: Houston, Brock Charles
• Format: Thesis
• Language: unknown
• Published: Digital Commons @ University of South Florida 2015
• Subjects: Otolith; oil spill; increment width analysis; microchemistry; Other Oceanography and Atmospheric Sciences and Meteorology; Red drum; Sciaenops ocellatus
• Online Access: https://digitalcommons.usf.edu/etd/5963; https://digitalcommons.usf.edu/context/etd/article/7159/viewcontent/Houston_usf_0206M_13230.pdf

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 ...