RAPID Deepwater Horizon Oil Spill: Impact of sub-surface oil plumes on mesopelagic micronekton

University Of South Florida, Tampa FL

Investigators

Abstract

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.