Comparison of the Spatial Extent, Impacts to Shorelines, and Ecosystem and 4-dimensional Characteristics of Simulated Oil Spills

The ever-growing increase in deep-sea oil explorations in the Gulf of Mexico (GoM) has been raising concerns with regard to future oil spills. Major oil spills in the GoM such as the Deepwater Horizon (DWH 2010) and the Ixtoc 1 (1979) resulted in extensive pollution of the pelagic, sea-floor, and coastal ecosystems. Oil spill transport and fate models are effective tools which allow a spatiotemporally explicit reconstruction of oil spills, while accounting for key processes such as evaporation, sedimentation, biodegradation, and dissolution. Oil transport data can be fed into an ecosystem model to help estimate system-scale changes in biodiversity and impacts on the delivery of ecosystem services. The increase in deep-sea oil-drilling endeavors warrants an evaluation of the potential outcomes and effects of oil spills. However, each spill scenario is a complex 4-D problem, spanning over wide spatiotemporal dimensions, affecting various media (water, sediments, coast, air); hence it is difficult to effectively evaluate the differences between various oil spill scenarios. In the current chapter, we examine quantifiable variables, which enable an effective comparison of the outcomes of four different scenarios: the DWH (DB_control), the DWH occurring during the fall (DB_Fall), east GoM scenario (DB_AL2), and west GoM scenario (DB_AL3). Specifically, we evaluate the total area and volume of oil-affected waters, the total water area and volume affected by toxic oil concentrations, the length of the shoreline affected by oil, and the total area of the sedimented oil. The oil transport model is coupled to Atlantis, a biogeochemical ecosystem model, to examine changes in the ecosystem biota. The depth and location of the oil vary with each scenario and so affect different habitats, species, and life stages. We consider relative impacts on pelagic and demersal food webs, shifts in age structure, changes in diet, and impacts on the sustainability of exploited species. We report the differences between the different oil spills and discuss their implications. Overall, the results differed slightly and not significantly between the four scenarios, ranked from most to least impactful: DB_AL2 \u3e DB_control \u3e DWH_Fall \u3e DB_AL3. This work suggests that a “DWH” occurring at a different time or place in the GoM would result in impact fairly similar to that occurred during the actual DWH. This is relevant given the extensive petroleum-related activity in the GoM

Evaluating the Effectiveness of Fishery Closures for Deep Oil Spills Using a Four-Dimensional Model

During the Deepwater Horizon (DWH) oil spill, extensive areas of the Gulf of Mexico (GoM) were closed for fishing due to the risk of seafood contamination and fishers’ health. The closures were determined daily according to the estimated extent of the spill relying mainly on satellite imaging. These closures were largely limited to the northern GoM. Yet, evidence from the field indicates a presence of oil beyond the closures, in some cases at toxic concentrations. With the advancement of oil transport modeling, together with the availability of new in situ data, we examine the 4D extent of the DWH spill, along with the effectiveness of the fishery closures in capturing the oil spill extent. We use the oil application of the Connectivity Modeling System (oil-CMS), cross-checked against in situ BP Gulf Science Data (GSD) and other published studies. The oil-CMS indicates that DWH extended well beyond the satellite footprint and fishery closures, with the closures capturing only ~55% of the total extent of the spill. With an increasing global shift toward deep-sea drilling, our findings are important for the safety of coastal communities and marine ecosystems around deep-sea drilling areas

Combined effects of oil exposure, temperature and ultraviolet radiation on buoyancy and oxygen consumption of embryonic mahi-mahi, Coryphaena hippurus

•Effects of oil-exposure, UV radiation and elevated temperature explored in embryonic mahi-mahi.•Exposed embryos displayed changes in buoyancy, sinking rate and energy utilization.•Findings imply embryos can sense and respond to external environmental cues.•Changes in vertical position in water column may have dire consequences for developing embryos. The Deepwater Horizon oil spill occurred in the summer of 2010 and coincided with the spawning window of the ecologically and economically important pelagic fish mahi-mahi (Coryphaena hippurus). During summer months, early life stage mahi-mahi were likely also exposed to other naturally occurring stressors such as increased temperature and ultraviolet radiation (UV). Previous research has shown that co-exposure to oil and additional natural stressors can affect the timing and duration of negative buoyancy in mahi-mahi embryos. The current study aimed to elucidate the factors affecting the onset of negative buoyancy and to also explore possible mechanisms behind buoyancy change. Embryos co-exposed to oil and/or increased temperature and UV radiation displayed early onset of negative buoyancy with concurrent increases in oxygen consumption and sinking rates, which are normally only seen during the period directly preceding hatch. Results also suggest a behavioral response in which embryos avoid UV radiation by sinking down the water column but reestablish positive buoyancy once the UV radiation is removed. These findings imply that embryos can dynamically change their position in the water column in response to external cues and thus may have much greater control over buoyancy than previously thought

Comparative Abundance, Species Composition, and Demographics of Continental Shelf Fish Assemblages throughout the Gulf of Mexico

We analyzed the results of the first comprehensive, systematic, fishery‐independent survey of Gulf of Mexico (GoM) continental shelves using data collected from demersal longline sampling off the United States, Mexico, and Cuba. In total, 166 species were sampled from 343 longline sets during 2011–2017, which deployed 153,146 baited hooks, catching 14,938 fish. Abundance, species richness, and Shannon–Wiener diversity indices by station were highest in mid‐shelf depths (~100 m), declining by about half in deeper waters. Six spatial assemblages were identified by testing the results of cluster analysis using similarity profile analysis and then plotting the geographic location of identified station clusters. A high degree of depth‐related and horizontal zonation was evident for demersal fish species. Multispecies CPUE (number per 1,000 hook‐hours) was highest off the north‐central (NC) and northwestern (NW) GoM and lower on the West Florida Shelf (WFS), Cuba (CUB), Yucatan Peninsula (YP), and southwestern (SW) GoM. Snappers and groupers were most abundant in the WFS and CUB, while elasmobranchs were the dominant taxa in the NC and NW GoM. Pelagic species were relatively rare everywhere (owing to the use of demersal longline gear), but were most dense off CUB. Species richness was highest in the NC and WFS subareas and lowest in the NW and CUB. Slopes of multispecies size spectra, which integrated mortality, recruitment, growth, and species interactions among size‐groups, were shallowest in the NW and NC GoM and steepest off the WFS and YP. These results provide a basis for evaluating the relative resiliency potential of species assemblages across the continental shelves of the GoM, and thus for identifying subareas that are most vulnerable to acute and chronic perturbations from cumulative effects of fishing, climate change, pollution (including oil spills), habitat loss, and invasive species