Graduation Year

2020

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Marine Science

Major Professor

Steven A. Murawski, Ph.D.

Committee Member

Mya Breitbart, Ph.D.

Committee Member

Larry Dishaw, Ph.D.

Committee Member

David Portnoy, Ph.D.

Committee Member

Cathy Walsh, Ph.D.

Keywords

biomarkers, oxidative stress, transcriptomics, toxicology, teleostCopyright

Abstract

A lack of baseline heath indices for offshore Gulf of Mexico (GoM) teleosts complicated impact assessments of the Deepwater Horizon (DWH) oil spill. While measurement of contaminant levels in fish after a pollution event can document exposure, such data fail to provide meaningful information about how this contact affects an animal's physiology. Controlled exposure studies have highlighted the utility of biomarkers that may indicate deleterious, long-lasting effects of pollutant exposure on various life stages of fish, however, their extrapolation to wild-caught, non-model species is challenging. In an increasingly chemically-saturated environment, it can also be difficult to separate the influence of chronic background contamination from that of a significant acute event, like an oil spill. This dissertation assessed the health of Golden Tilefish (Lopholatilus chamaeleonticeps) and Red Snapper (Lutjanus campechanus) caught throughout the GoM in 2015-2017, using both biomarkers of oxidative stress and immune response, and transcriptomics. Samples were collected several years after the DWH event, therefore, this study investigated putative lasting effects of exposure on benthic and reef-associated fishes.

In Chapter II, the first known reference intervals for oxidative stress and immune system biomarkers were created for Golden Tilefish (n = 255) and Red Snapper (n = 125) from the GoM, consistent with guidelines of the American Society for Veterinary Clinical Pathology. This included intervals for: malondialdehyde, sorbitol dehydrogenase, sum erythrocyte nuclear abnormalities, superoxide dismutase, hematocrit, leukocrit, lysozyme, and differential white blood cell counts. Species differences were observed, indicating higher levels of genotoxicity and antioxidant response in Golden Tilefish than in Red Snapper, throughout the GoM.

Chapters III and IV compared the relationships between biomarker response and polycyclic aromatic hydrocarbon (PAH) exposure in Golden Tilefish and Red Snapper, respectively. Fish included in this study were selected only when a sufficient number of specimens (n ≥ 3) were caught at each sampling station, and sampling stations were grouped into defined geographic zones. Temporal variation in biomarker response at north central GoM stations (where the DWH event occurred) sampled in both 2015 and 2017 was also evaluated. Results reported in chapter III indicated differential biomarker patterns in Golden Tilefish collected from the north central GoM compared to those from other regions and evidence was observed for a possible compensatory metabolic shift due to chronic PAH contamination. Chapter IV revealed limited negative health effects from background PAH exposure on Red Snapper in the northern GoM, however, possible maternal offloading of PAHs was noted in fish from the north central GoM, which may have influenced observed biomarker response.

In chapter V, next generation RNA sequencing was utilized to determine whether geographically grouped populations of Golden Tilefish (n = 15) had signatures of differential gene expression, and if these differences may be attributed to PAH exposure. The first de novo assembly of the Golden Tilefish transcriptome was performed, and differential gene expression was compared in female fish caught from the De Soto Canyon, Campeche Bay, and the Yucatan Peninsula. Patterns of differential expression were observed between groups. Fish collected within the De Soto Canyon, likely exposed to DWH oil, displayed an altered metabolic response, activated pathways of cellular debris clearance, and down-regulation of reproductive genes compared to the other regions. These results support the compensatory metabolic shift hypothesis in fish with ongoing exposure to PAHs in the region. Golden Tilefish sampled from the oil fields of Campeche Bay, Mexico, displayed possible immunosuppression and reduced protective mechanisms, despite evidence of oxidative-stress-induced damage, which may indicate an acute response to contaminant exposure. Fish collected offshore the Yucatan Peninsula had more similar patterns of gene expression to fish from the De Soto Canyon than those from Campeche Bay, possibly as a result of significant variation in Campeche Bay specimens. The transcriptome suggest further exploration of pathways involved with lipid and carbohydrate metabolism, oxidative stress and clearance of cellular damage, and reproduction may be useful for PAH-related work in wild-caught teleosts. Furthermore, this study demonstrated the utility of pooling individuals from field sites to yield targets for data exploration.

This work adds significantly to an understanding of the health of non-model, offshore teleosts in the GoM. While variation in biomarker response was observed throughout dispersed regions of the GoM, likely in relation to the varying stressors and contaminants dominating each system, both Red Snapper and Golden Tilefish appear resilient. Despite possible acclimation to adverse conditions, the Deepwater Horizon oil spill continued to impart sublethal effects on Golden Tilefish through 2017. The long-term effects of putative reproductive suppression and metabolic shifts in these organisms warrant further monitoring and analysis.

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