The impact of the Deepwater Horizon blowout on historic shipwreck-associated sediment microbiomes in the northern Gulf of Mexico

Abstract

More than 2,000 historic shipwrecks spanning 500 years of history, rest on the Gulf of Mexico seafloor. Shipwrecks serve as artificial reefs and hotspots of biodiversity by providing hard substrate, something rare in deep ocean regions. The Deepwater Horizon (DWH) spill discharged crude oil into the deep Gulf. Because of physical, biological, and chemical interactions, DWH oil was deposited on the seafloor, where historic shipwrecks are present. This study examined sediment microbiomes at seven historic shipwrecks. Steel-hulled, World War II-era shipwrecks and wooden-hulled, 19th century shipwrecks within and outside of the surface oiled area and subsurface plume were examined. Analysis of 16S rRNA sequence libraries, sediment radiocarbon age data, sedimentation rates, and hydrocarbons revealed that the German U-boat U-166 and the wooden-hulled sailing vessel known as the Mardi Gras Wreck, both in the Mississippi Canyon leasing area, were exposed to deposited oil during a rapid sedimentation event. Impacts to shipwreck microbiomes included a significant increase in Piscirickettsiaceae-related sequences in surface sediments, and reduced biodiversity relative to unimpacted sites. This study is the first to address the impact of the spill on shipwreck-associated microbiomes, and to explore how shipwrecks themselves influence microbiome diversity in the deep sea.

Deep-Sea Biofilms, Historic Shipwreck Preservation and the Deepwater Horizon Spill

“…Stout et al (2017) described the footprint of spillderived hydrocarbons on the seafloor across the study area, and an acute fallout plume in the Mississippi Canyon lease area, where U-166 and the Mica wreck are located, shortly after the spill, and in 2014, when the experiments in this study were initiated. The residual impacts to the seabed at sites in this study are described in detail in Hamdan et al (2018). There is geological and biogeochemical evidence of spill residues at the U-166 site, as revealed by a ∼5 cm layer of oil flocculant on the seafloor that has a radiocarbon signature inconsistent with riverine sediment.…”

“…Work was conducted during two expeditions on board R/V Pelican: PE14-15 and PE15-02 in March and July 2014, respectively, as part of the Gulf of Mexico Shipwreck Corrosion, Hydrocarbon Exposure, Microbiology, and Archaeology (GOM-SCHEMA) project. Five historic shipwrecks were selected (Figure 1) (Damour et al, 2016;Hamdan et al, 2018). A sixth site, the Viosca Knoll Wreck was planned, but weather delays during PE14-15 did not allow for placement of biofilm experiments.…”

“…An acute footprint of oil spillderived contamination was in an area ∼16 km southwest of the Macondo wellhead (Stout et al, 2017). This area contains two steel-hulled historic shipwrecks, the German submarine U-166, and the passenger and freight steamer Robert E. Lee (Damour et al, 2016;Hamdan et al, 2018). Hamdan et al (2018) provides evidence that U-166 was exposed to the fallout of oil from the spill, and that the microbiomes of sediment surrounding U-166 still presented evidence of contamination 4 years after the spill.…”

“…This area contains two steel-hulled historic shipwrecks, the German submarine U-166, and the passenger and freight steamer Robert E. Lee (Damour et al, 2016;Hamdan et al, 2018). Hamdan et al (2018) provides evidence that U-166 was exposed to the fallout of oil from the spill, and that the microbiomes of sediment surrounding U-166 still presented evidence of contamination 4 years after the spill. The proximity of these shipwrecks to the Macondo wellhead, the observed shift in sediment microbiomes toward oil-degrading bacteria, and location within the spill footprint raises questions about the potential for oil-enhanced MIC and impacts to the preservation of historic shipwrecks.…”

Biogeochemical Consequences of Nonvertical Methane Transport in Sediment Offshore Northwestern Svalbard

“…Genomic DNA was extracted using a modified FastDNA™ protocol described in detail by Hamdan et al (2013) and Hamdan et al (2018). DNA was quantified on a Qubit 2.0 Fluorometric Quantitation system (Invitrogen), and purity was determined by NanoDrop (ThermoFisher).…”