Deep-Sea Benthic Footprint of the Deepwater Horizon Blowout

Abstract

The Deepwater Horizon (DWH) accident in the northern Gulf of Mexico occurred on April 20, 2010 at a water depth of 1525 meters, and a deep-sea plume was detected within one month. Oil contacted and persisted in parts of the bottom of the deep-sea in the Gulf of Mexico. As part of the response to the accident, monitoring cruises were deployed in fall 2010 to measure potential impacts on the two main soft-bottom benthic invertebrate groups: macrofauna and meiofauna. Sediment was collected using a multicorer so that samples for chemical, physical and biological analyses could be taken simultaneously and analyzed using multivariate methods. The footprint of the oil spill was identified by creating a new variable with principal components analysis where the first factor was indicative of the oil spill impacts and this new variable mapped in a geographic information system to identify the area of the oil spill footprint. The most severe relative reduction of faunal abundance and diversity extended to 3 km from the wellhead in all directions covering an area about 24 km2. Moderate impacts were observed up to 17 km towards the southwest and 8.5 km towards the northeast of the wellhead, covering an area 148 km2. Benthic effects were correlated to total petroleum hydrocarbon, polycyclic aromatic hydrocarbons and barium concentrations, and distance to the wellhead; but not distance to hydrocarbon seeps. Thus, benthic effects are more likely due to the oil spill, and not natural hydrocarbon seepage. Recovery rates in the deep sea are likely to be slow, on the order of decades or longer.

Community response of deep-sea soft-sediment metazoan meiofauna to the Deepwater Horizon blowout and oil spill

“…In Montagna et al (2013), principal components analysis (PCA) was used to classify the biological and environmental variables in a combined analysis to estimate the benthic footprint of the DWH blowout and oil spill. PCA is a variable reduction technique that can be used to reduce a large number of variables to a reduced set of new variables which are uncorrelated and contain most of the variance in the original data set.…”

“…These estuarine and shallow-water coastal investigations have documented impacts to salt marshes and associated communities (McCall & Pennings 2012, Silliman et al 2012, and benthic microbial and eukaryote communities (Kostka et al 2011, Bik et al 2012, Lu et al 2012, Mason et al 2012, and there has been extensive reporting of water-column microbial response to the DWH-derived hydrocarbons (Kessler et al 2011, Valentine et al 2014. However, few studies to date have documented deep-sea benthic impacts of the DWH oil spill (White et al 2012, Montagna et al 2013, Fisher et al 2014.…”

“…The deep-sea benthic chemical and biological footprint of severe to moderate impacts from the DWH blowout and oil spill encompassed an approximate area of 172 km 2 in the vicinity of the wellhead and in the southwestern trajectory of the deepwater oil plume (Montagna et al 2013). The footprint was characterized by high PAH, barium, and total petroleum hydrocarbon chemical loads with concomitant low meiofaunal and macrofaunal diversity and an elevated nematode to copepod ratio (N:C).…”

“…The footprint was characterized by high PAH, barium, and total petroleum hydrocarbon chemical loads with concomitant low meiofaunal and macrofaunal diversity and an elevated nematode to copepod ratio (N:C). Although Montagna et al (2013) used meiofauna community metrics of abundance, diversity, and N:C to define the DWH benthic footprint, differences in community structure between impact zones was not included in that analysis. Therefore, the present study further analyzes the metazoan meiofauna community and fully describes community structure patterns across the 58 stations that were categorized with respect to the DWH benthic footprint (Montagna et al 2013).…”

“…Although Montagna et al (2013) used meiofauna community metrics of abundance, diversity, and N:C to define the DWH benthic footprint, differences in community structure between impact zones was not included in that analysis. Therefore, the present study further analyzes the metazoan meiofauna community and fully describes community structure patterns across the 58 stations that were categorized with respect to the DWH benthic footprint (Montagna et al 2013). Additionally, major taxonomic diversity and N:C are assessed spatially in relation to the DWH wellhead at 66 total stations to test the hypothesis that additional spatial resolution will improve estimates of the actual extent of DWHderived impacts to deep-sea soft-sediment community structure.…”