A multiple endpoint analysis of the effects of chronic exposure to sediment contaminated with Deepwater Horizon oil on juvenile Southern flounder and their associated microbiomes

Abstract

Exposure to oiled sediments can negatively impact the health of fish species. Here, we examine the effects of chronic exposure of juvenile southern flounder, Paralichthys lethostigma, to a sediment-oil mixture. Oil:sediment mixtures are persistent over time and can become bioavailable following sediment perturbation or resuspension. Juvenile flounder were exposed for 32 days under controlled laboratory conditions to five concentrations of naturally weathered Macondo MC252 oil mixed into uncontaminated, field-collected sediments. The percent composition of individual polycyclic aromatic hydrocarbons (PAHs) of the weathered oil did not change after mixing with the sediment. Spiked exposure sediments contained 0.04-395mg/kg tPAH50 (sum of 50 individual PAH concentration measurements). Mortality increased with both exposure duration and concentration of sediment-associated PAHs, and flounder exposed to concentrations above 8mg/kg tPAH50 showed significantly reduced growth over the course of the experiment. Evident histopathologic changes were observed in liver and gill tissues of fish exposed to more than 8mg/kg tPAH50. All fish at these concentrations showed hepatic intravascular congestion, macrovesicular hepatic vacoulation, telangiectasia of secondary lamellae, and lamellar epithelial proliferation in gill tissues. Dose-dependent upregulation of Cyp1a expression in liver tissues was observed. Taxonomic analysis of gill and intestinal commensal bacterial assemblages showed that exposure to oiled sediments led to distinct shifts in commensal bacterial population structures. These data show that chronic exposure to environmentally-relevant concentrations of oiled sediments produces adverse effects in flounder at multiple biological levels.

Crude oil impairs immune function and increases susceptibility to pathogenic bacteria in southern flounder

“…There were four treatments: 1) Control (No Oil/No Pathogen challenge), 2) Oil exposure without pathogenic bacteria challenge (Oil/No Pathogen challenge), 3) No oil exposure followed by pathogenic bacteria challenge (No Oil/Pathogen challenge), and 4) oil exposure with pathogenic bacteria challenge (Oil/Pathogen challenge). Oil-contaminated sediment exposures (Oil/No Pathogen challenge and Oil/Pathogen challenge) were performed by mixing uncontaminated field collected sediment (30.37937, -88.30678 collected on 05/15/2013) with a sample of weathered oil ([42] that was collected from the nGoM on July 1, 2010 (Slick B). The concentration of the oil in the artificially contaminated sediment was measured to be 57.4 mg/kg of sediment tPAH50 (the sum of 50 individual PAH concentration measurements).…”

“…Composite sediment and water samples were analyzed for PAH composition following the procedure discussed in Brown-Peterson et al (2015) (S2 Table). This concentration was selected as it is environmentally relevant to the Gulf Coast following the oil spill [43] and is a concentration we have previously demonstrated to have adverse effects in flounder [42]. …”

Generation of red drum (Sciaenops ocellatus) hematology Reference Intervals with a focus on identified outliers

“…When weathered DWH oil infiltrated coastal habitats in Gulf States, fish were likely exposed to water‐borne oil, oil‐contaminated sediment through direct contact, and possibly through ingestion of oil‐contaminated prey. In various studies, DWH oil caused a variety of adverse health effects in juvenile and adult fish, including immune and cardiac dysfunction, developmental abnormalities (eg, skeletal defects), and growth impairment …”

Responses of juvenile southern flounder exposed to Deepwater Horizon oil‐contaminated sediments

“…Previously, we reported the results of a chronic laboratory exposure where southern flounder were exposed to reference sediments mixed with increasing concentrations of weathered Deepwater Horizon oil for 32 d . That exposure resulted in reduced survival and growth, alterations of gill and liver histopathology, gene expression changes, and altered microbiome in gills and intestines.…”