USING MID-OUTER SHELF FORAMINIFERA TO ASSESS BENTHIC COMMUNITY DAMAGE AND RECOVERY FOLLOWING THE DEEPWATER HORIZON OIL SPILL, GULF OF MEXICO

The explosion on the oil platform Deepwater Horizon on April 20, 2010, killed 11 crewmen and was followed by uncontrollable fire and sinking of the rig 2 days later, leaving a gushing wellhead at a water depth of 1,259 m. Difficulties in capping the wellhead at this great depth resulted in the largest offshore oil spill in U.S. history: as much as 4.9 million barrels of crude oil were released before the flow was stopped on July 15. Aggressive applications of dispersants and clean-up efforts near shore kept much of the shoreline from being as impacted as was initially predicted. By the end of the summer, most of the oil had apparently disappeared. However, independent lines of research now point to its sinking to the seafloor offshore, where benthic communities could have been severely compromised.

Because of their utility in exploration for hydrocarbon reserves, benthic foraminifera in the Gulf of Mexico have long been studied from the standpoint of systematics and present-day distribution. In recent decades, near-shore species have also been incorporated in environmental studies. Crude-oil contamination of marine environments elsewhere has been shown to produce developmental abnormalities in benthic foraminifera, such as the small size and distorted shapes of new chambers. Affected foraminifera are more likely to become parasitized, and both diversity and abundance may decrease markedly. With rapid addition of chambers and relatively short life spans, they respond rapidly to contamination events and, unlike soft-bodied benthic invertebrates, their mineralized tests persist as a long-lasting record of initial damage to for­­­­­aminiferal communities and their later recovery.

The current study joins a broader, ongoing NOAA-funded survey of meiofauna west to east across the Gulf, with most stations at mid- to outer-shelf and upper-slope depths. In October-November 2010, cores were taken in Shipek grab samples for analysis of foraminifera as part of a new phase of the study funded by British Petroleum. In addition to species identifications, assemblage compositions, and live-dead ratios, the types and percentages of abnormalities are being recorded for each species. Those sites particularly affected will be targeted for re-sampling in Fall 2011 in order to gather data on the rate of recovery of benthic communities.