Intellectual merit. The recent discovery of subsurface oil plumes in the northern Gulf of Mexico (GOM) at mesopelagic (200-1000 m) depths brings the threat of oil exposure to a critical link in the open ocean trophic pyramid: the pelagic deep-sea community. Petroleum hydrocarbons have been identified at depths of 400 and 1000 m in the northern GOM. Extensive use of dispersants and a very deep well-head raise the likelihood of a substantial interaction between the mesopelagic community and petroleum hydrocarbons originating at the Deepwater Horizon well site. Until now, the deep pelagic ecosystem has remained largely free of oil-derived pollution and its inhabitants are likely to be very sensitive to it.
The mesopelagic micronekton/macrozooplankton assemblage of the GOM is both highly diverse and vertically mobile. The great majority of the fish and crustacean species reside at depths below 600 m during the day, performing a migration into the upper 250 m at night. Thus, chances of mid-water species encountering subsurface oil plumes are extraordinarily high. Briefly put, if the plumes are present, a large fraction of the mid-water community will be migrating through them.
This research project will: (1) obtain data on present-day micronekton species composition, distribution, and abundance in the upper 1000 m of the water column using ships of opportunity, and compare those data with those acquired in previous decades; (2) evaluate the degree to which the community has already been exposed to subsurface oil plumes using GCMS analysis of hydrocarbon fractions in organismal tissues, and comparing those results with previously collected specimens maintained at -80o; (3) evaluate the variability in sources of carbon and nitrogen supporting mesopelagic biomass and determine the trophic position of present day and previously collected specimens using d13C and d15N of muscle tissue. The data collected in this project will provide a stable isotope baseline allowing for evaluation of present and future subsurface oil impact.
Broader impacts. Broader impacts include training a postdoctoral fellow in shipboard sampling, the biology of mesopelagic fauna, and basic geochemical methodologies and data interpretation. The PIs have established regular interactions with TV and newspaper reporters have been on the forefront of the shipboard sampling and geochemical analyses that first described the subsurface plumes emanating from the oil spill. Interaction with print and visual media will continue throughout the study as the oil spill coverage continues.
The explosion of the Deepwater Horizon (DWH) drilling rig resulted in the largest offshore oil spill in U.S. history, releasing more than 4.5 million barrels of oil into the Gulf of Mexico (GOM) in only 86 days. The spill occurred under a unique set of circumstances: the broken well-head was deep (>1.1 km below the sea surface), chemical dispersants were released at depth, and several sub-surface plumes of oil were detected, some of which persisted for months without substantial biodegradation. We measured chemical indicators of oil exposure in deep-living fish and shrimp species that may have either encountered oil in the subsurface plumes, or ingested contaminated prey because of their daily migrations from deep waters to or near the surface ocean at night, and back again to depth (about 600 m) during the day. Samples of fish and shrimp were collected using trawls fishing from the surface to 1000 m in the DeSoto Canyon, a deep marine canyon adjacent to the Deepwater Horizon well. We looked for evidence of oil exposure by chemically comparing specimens collected prior to, six weeks after, and one year after the oil spill (2007, 2010, and 2011). We found evidence of exposure to oil in the deep-sea fauna, and incorporation of trace amounts of oil into the deep-sea food chain. Our written results will be reported in the technical scientific literature, and have been reported at scholarly meetings as well as at conferences on oil spill impacts. Participants in the project included a large number of university students, faculty, and staff, a representative of the Florida Department of Environmental Protection, a K-12 educator, journalists, and photographers. Preliminary findings were reported in the Saint Petersburg Times, on the USF College of Marine Science website, and on local Bay News 9 news reports.
