NRDA: Deepwater ROV Sampling to Assess Potential Impacts to Hardbottom Coral Communities and Associates from the Deepwater Horizon Oil Spill

Science Center Objects

The MC252 oil spill introduced hydrocarbons, dispersants, and drilling muds into the Gulf of Mexico, potentially adversely affecting the seafloor environment surrounding the spill site. 

A comparison of normal coral with some dead skeletal material
A comparison of normal coral with some dead skeletal material covered by typical secondary colonization (right) and a wilting, dying coral covered with oil plume debris (left). Image courtesy of, Lophelia II 2010, NOAA OER and BOEM

The Science Issue and Relevance: The MC252 oil spill introduced hydrocarbons, dispersants, and drilling muds into the Gulf of Mexico, potentially adversely affecting the seafloor environment surrounding the spill site. While approximately 99% of the seafloor in the GOM is soft sediment, hard bottom environments punctuate the vast sediment environment as islands in a sea of mud. Hard bottom habitats and associated communities are known to harbor substantial levels of biodiversity and complexity, including deep-sea corals. Following the spill, hard bottom communities were recently identified in proximity to the wellhead, including corals that were covered in a brown flocculent material (see figure 1 to left). However, the impact of the spill on these systems remains unclear. Scientists within the Natural Resource Damage Assessment Deepwater Horizon Deepwater Benthic Trustees Working Group are examining deep-sea coral ecosystems in the GOM to quantify the exposure and injury from the oil spill to corals, associates, and surrounding environment. Deep coral ecosystems are of interest because the corals are long-lived and are sensitive to human activities including bottom trawling, anchoring, pollution, and offshore oil and gas development. Sediments adjacent to deep-sea corals contain infauna, including macrofauna (> 0.3 mm) and meiofauna (> 0.045 mm). Certain infauna are known to be sensitive to disturbance, including pollution, and their recovery in the deep sea may take decades to millennia, depending on the type of disturbance. Better understanding of these animals is imperative, as they serve several important ecosystem functions, including bioturbating and aerating sediments, stimulating microbial activity, affecting the cycling of pore-water nutrients and chemicals, and serving as food for higher trophic levels such as fish and larger invertebrates. This research will provide information on the potential impact of the oil spill to sediment macrofauna and meiofauna and represents a component of a larger NRDA ecosystem assessment that includes high resolution imagery, molecular, histopathological, and chemical analyses to provide a comprehensive understanding of the impacts of the spill to these systems.

This push core shows discrete layers in a typical sediment sample
This push core shows discrete layers in a typical sediment sample. 

Methodology for Addressing the Issue: The primary objective of this work is to collect sediment and sediment-dwelling biota for analysis of potential MC 252 hydrocarbon and dispersant concentrations and oil identification, to measure population densities of sediment dwelling fauna, and quantify potential lesions and other pathologies in the sediment-dwelling biota. Sediments surrounding deep coral habitats within 200 km of the wellhead were sampled from 2011-2015, including Lophelia pertusa habitats previously sampled in 2009 and 2010. In situ, quantitative sediment samples for meio- and macrobenthic (< 1 mm) communities and their environment (e.g., hydrocarbons, particle size, organic carbon, nitrogen, dispersants, metals, redox, and salinity) were collected using an ROV deployed push cores.

Future Steps: Data collected are being processed and analyzed to determine the potential impact of the spill on sediment fauna. The abundance, composition, and diversity of the infauna are being quantified from the cores, and the biota are being examined for lesions and other visible pathologies that may be diagnostic of exposure to the spill. As oil and gas exploration in the GOM increases, so does the possible risk for additional catastrophic oil spills and associated impacts to fisheries, coastlines, and deep-sea environments. Our study will provide an understanding of impacts of these activities on seafloor communities and the time scales required for potential recovery of sediment benthos. This information can be used to help inform the development of educated management decisions regarding protecting and conserving these sensitive ecosystems.

Related Project(s): Benthic Ecology, Trophodynamics, and Ecosystem Connectivity: Lophelia II: Continuing Ecological Research on Deep-Sea Corals and Deep Reef Habitats in the Gulf of Mexico

Publications:

Prouty, N.G., Fisher, C.R., Demopoulos, A.W.J., and Druffel, E.R., 2014, Growth rates and ages of deep-sea corals impacted by the Deepwater Horizon oil spill: Deep Sea Research Part II: Topical Studies in Oceanography, In Press, doi:10.1016/j.dsr2.2014.10.021, IP-056047

Fisher, C.R., Demopoulos, A.W.J., Cordes, E.E., Baums, I.B., White, H.K. and Bourque, J.R., 2014, Deep-sea coral communities as indicators of ecosystem level impacts resulting from the Deepwater Horizon oil spill: Bioscience, v. 64, no. 9, p. 796-807, doi:10.1093/biosci/biu129, IP-055458

Cordes, E.E., Berlet, S.P., Cardman, Z., Dannenberg, R., Demopoulos, A.W.J., Georgian, S.E., King, C., McKean, D.L., and Young, D.M., 2014, Exploring deep-sea coral communities and the effects of oil and gas inputs to the Gulf of Mexico: Oceanography, v. 27(supplement), no. 1, p. 34-35, doi:10.5670/oceanog.2014.supplement.01.

White, H.K., P. Hsing, W. Cho, T. M. Shank, E.E. Cordes, A.M. Quattrini, R.K. Nelson, R. Camilli, A. W. J. Demopoulos, C.R. German, J.M. Brooks, H.H. Roberts, W. Shedd, C. M. Reddy, and C. R. Fisher. 2012. Impact of the Deepwater Horizon oil spill on a deep-water coral community in the Gulf of Mexico. PNAS. doi:10.1073/pnas.1118029109