Lasting Impact and Recovery From the Deepwater Horizon Oil Spill of a Deepwater Coral Community in the Gulf of Mexico

Open Access
Author:
Fu, Bo
Area of Honors:
Biology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Charles Raymond Fisher Jr., Thesis Supervisor
  • Stephen Wade Schaeffer, Honors Advisor
Keywords:
  • coral
  • deepwater horizon
  • oil
  • gulf of mexico
  • hydroid
Abstract:
The Deepwater Horizon rig blowout released an estimated 4.1 million barrels of oil, as much as half of which remained in the water column or was deposited onto the seafloor, posing a high risk to deepwater ecosystems. A coral community in BOEM lease block MC294, located 11km from the Macondo well at a depth of 1370m, was discovered in 2010 with many corals showing signs of impact from the blowout. A paper published by Hsing and colleagues (2013) found the median total visible impact of the corals at this site decreased between November 2010 and March 2012, correlating the degree of initial impact with lasting damage. Here, we present a follow-up study, expecting similar decreases in median total visible impact and the continued presence of hydroid colonization. Through a series of eight research expeditions between November 2010 and June 2014, 49 Paramuricea biscaya corals were imaged and digitized. Individual branches were categorized into four different categories depending on visible condition. Images were then compared between visits for transitions from one category to another, producing detailed temporal data of condition. The overall median visible impact of the corals decreased significantly between late 2010 and October 2011, but showed no significant changes after. We found significant rates of branch loss between March 2011 and June 2013, up to a peak of 0.72 break points per coral per month between November 2012 and June 2013. On 24 out of 39 corals, portions of hydroid-colonized branches recovered to a non-visibly impacted state, though the degree of recovery was small compared to the amount of hydroids that remained on the coral. Continual changes in hydroid composition and branch loss indicate the corals are still in a state of flux, and despite permanent damage from by branch loss, overall the data suggests that the level of impact has leveled off.