Effects of Oil on the Deep Gulf of Mexico Benthos
Washburn, Travis William
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The deep sea ( > 200 m) is the largest habitat on Earth. However, the deep sea ecosystem is poorly understood relative to most other habitats due to the difficultly in accessing it. As human activities increase in the deep sea, the need to understand processes occurring in the deep and impacts on these processes by human activities also increases. This study examines the importance of the deep sea to humans as well as the impacts of oil on deep-sea communities. Approximately 5 million barrels of oil were released during the Deepwater Horizon spill, much of which remained in the deep sea. Shortly after the spill ended, benthic diversity and abundance were lower near the Deepwater Horizon wellhead compared to deep-sea areas not affected by the spill. Diversity increased with increasing distance from the wellhead while abundances peaked at intermediate distances suggesting a toxicity vs. enrichment effect. There were also several benthic taxa identified as potential indicators of oil-contaminated and uncontaminated areas. Oil is released from the seafloor via natural seepage as well. Benthic abundance and diversity differed among different types of seep communities (microbial mats, tubeworms, and soft-bottom seeps), between seep and non-seep areas, and between seep and spill areas. Unlike communities impacted by the DWH spill, there did not appear to be taxa specifically associated with natural seepage. In fact, high variability in community structure appeared to be the best indicator of natural seepage, with specific seep communities not only different from background and spill communities, but also different from other seep communities. Oil that enters the oceans does not remain there indefinitely. Oil released by both natural and anthropogenic processes is removed from the marine environment naturally by burial in the seafloor, degradation by bacteria, and dilution in the water column. The removal of oil by the environment is an example of an ecosystem service termed waste regulation. Waste regulation was examined in the context of the Deepwater Horizon spill by calculating the monetary value of the natural removal of oil spilled. Estimations of fates of the DWH oil as well as cleanup costs were examined. It was estimated that 10’s of billions of dollars were saved from offshore waste regulation following the spill. This dissertation concludes that the differences among communities at natural seeps, areas impacted by the spill, and areas not impacted by oil were numerous. Benthic communities associated with deep oil spills were defined, allowing for the future assessment of damages caused by deep-sea spills. Communities associated with natural seepage were different from other habitats as well as other seep communities, emphasizing the unique nature of each seep location in the Gulf of Mexico. Valuation of deep-sea services will provide monetary costs for destructive practices in the deep sea. Knowledge of deep-sea services is also important to communicate to the public to ensure these services will be protected. This dissertation provides information on the effects of the first deep-sea oil release on benthic communities, differences between impacts of natural and anthropogenic oil required to assess spill damages, a unique comparison of several different seep communities throughout the Gulf of Mexico, as well as an initial, partial value of waste regulation provided by the deep-sea environment. The work performed can help guide future policies concerning deep-sea drilling and assist in the identification and protection of unique habitats in the deep sea. Communication of deep-sea benefits can provide the public with motivation to care about the fate of the deep sea, which is far beyond the reach of most people.