On April 22, 2010, the drill platform Deepwater Horizon sank in nearly 1,200 m of water in the northern Gulf of Mexico. Since this date various estimates of oil and added chemical dispersants have been released from the site with dispersion both at the surface and at depth. The transport of this oil and dispersants has been influenced by wind-driven currents over the shelf and by the Loop Current and its derivatives offshore. To date the exact amount and paths of movement of the Horizon spill remain speculative. Since 2003, with funding from the National Oceanic and Atmospheric Administration (NOAA, this group of investigators has conducted 5 summer cruises in the northern Gulf of Mexico using high-resolution sampling to define the spatially explicit relationships the physical environment and pelagic zooplankton and fish. Thus, this research group has one of the most comprehensive, synoptic data sets on temperature, salinity, oxygen, phytoplankton, zooplankton and fish in the northern Gulf of Mexico for conditions prior to the oil leak.
The current RAPID award will allow this group to repeat their high-resolution mapping of hydrography, oxygen, plankton and fish in the northern Gulf of Mexico. The study will cover the previous survey region in the hypoxic zone west of the Mississippi Delta and the area east of the Mississippi where more oil transport from the spill is expected. The cruise will take place in the late summer period because the investigators have 5 years of baseline data during this season to compare the results. The measures of species diversity and abundance, biomass size spectrum, fish diets, fish growth rate potential and the results produced from their use of ecosystem models will be extremely useful to assess the possible effects of the oil spill on the living resources of the northern Gulf of Mexico. This group also will send scientists on the ORV Oceanus to conduct high resolution vertical zooplankton measurements and MOCNESS zooplankton tows at deeper stations and broader mapping surveys to extend our spatial coverage of the affected area. They will coordinate our zooplankton and fish measurements with other investigators assessing the biogeochemical and biological impacts of the BP oil spill. Data from previous NOAA studies will be deposited in the NSF Biological NSF Biological and Chemical Oceanographic Data Management facility.
Broader Impacts. Given the economic importance of the Gulf of Mexico commercial fisheries (about 20% of the U.S. total landings representing about $991 million) and recreational fishing (generating ~30% of the nation's saltwater fishing expenditures and supporting nearly 25% of the nation's recreational saltwater jobs), it is imperative that knowledge of the effects of the BP oil spill on the pelagic ecosystem be assessed. The Horn Point Laboratory and Oregon State University are part of the National Science Foundation Center for Ocean Sciences Education Excellence (NSF-COSEE) and Experience for Undergraduates (REU) programs. Where possible in this NSF RAPID response grant, we will involve REU undergraduate students and teachers in our proposed research program.
The recent unprecedented events in the Gulf of Mexico, the MC252 oil spill in 2010 and record flooding of the Mississippi River in 2011, are likely to have far reaching impacts on many aspects of the northern Gulf of Mexico pelagic ecosystem. We collected high resolution data on the physical conditions, fish resources, and plankton populations during a cruise in September 2010 on the Louisiana continental shelf. The purpose of this was to compare the results from 2010 with earlier work we conducted in that region to determine if there were measurable impacts of the spill. In addition, we provided personnel to participate in zooplankton sampling offshore, near the site of the spill to assess the direct impact of the spill on those animals. We found that near the site of the spill, oil residues were found in zooplankton, with signatures of fresh material found in animals collected in deep water, and weathered material found in animals collected in surface water. This work was part of collaboration between a number of researchers on our team and was published in the Journal of Geophysical Letters (Mitra et al. 2012). When we compared the results from our cruise on the continental shelf to observations made during earlier work in the same region, we were not able to discern any major impacts on plankton and fish. This region includes the "Dead Zone", an area of depleted oxygen that occurs every summer on the Louisiana shelf. Data from net tows, pump and niskin bottle samples, optical plankton counters, fish trawls, and hydrographic instruments were used to compare zooplankton community structure and physical characteristics between years and across this region. We found that for the earlier data (2003-2008) the most important conditions to predict the zooplankton community were temperature and salinity in the water, and when we did analysis using the 2010 data, that same pattern was observed. Data from 10 acoustic surveys showed that pelagic fish abundance was higher near shore and decreased offshore during 2010 sampling. High densities of fish were not found in areas of low DO. These data, along with hydrographic data and acoustic surveys from 2003-2008, are now accessible through a Matlab-compatible data management system, which will be made publically available. In addition, we sampled over 50 different species of fish through 18 midwater trawl surveys at 13 stations on 6 transect lines. The most commonly observed species in 2010 was Atlantic croaker (N = 243, mean length = 140mm (range = 90-190cm)), followed by cutlassfish, longspine porgy, striped anchovy, and Atlantic bumper. Acoustic surveys and fish species data will be used along with temperature and DO data in growth rate potential models to determine areas of the northern Gulf of Mexico that provide suitable habitat for fish growth. Data from this project was submitted to the The Biological and Chemical Oceanography Data Management Office (BCO-DMO) and can be accessed at the following URL: http://osprey.bco-dmo.org/project.cfm?id=137&flag=view
