TEST ABNORMALITIES IN BENTHIC FORAMINIFERA FROM THE ORANGE BEACH AREA, ALABAMA: ASSESSING THE EFFECTS OF THE DEEPWATER HORIZON OIL SPILL

The Deepwater Horizon explosion in April of 2010 marked the beginning of the largest offshore oil spill in U.S. history. In spite of massive applications of dispersants and clean-up efforts, oil impacted Alabama beaches in the early summer. By the end of the summer, most beaches had been cleaned, and oil had apparently disappeared from the Gulf. However, Tropical Storm Lee in September 2011 resulted in fragments of what are believed to be submerged tar mats washing up on beaches, especially in the area of Orange Beach, AL. The impact of the spill on marine life, including benthic communities, some of which may still be subjected to hydrocarbon mats that have sunk to the seafloor, is the subject of ongoing research. Benthic foraminifera are used as bio-indicators because hydrocarbon contamination induces growth deformities and, unlike soft-bodied benthos, their mineralized tests persist as a long-lasting record of their existence and their health.

Sampling along a 5-mile-long, north-south transect south of Orange Beach and from sites further west was done at approximately 3-month intervals: July 2011, September 2011, and January 2012. A multicorer with 4-inch diameter tubes was used, with the top 2-3 cm of sediment recovered from cores and preserved immediately in buffered formalin. In the laboratory, a sub-sample was stained with Rose Bengal in order to recognize live individuals and sieved at 63 μm. Stained specimens and well-preserved dead tests were picked from the residue.

Assemblages of foraminifera recovered were dominated by species of Ammonia and Elphidium. Aberrant specimens of Ammonia include those with final chambers that are abnormally large or small, have laterally compressed tests, or have tests with an unusually high spiral side. In Elphidium, some tests have an irregular outline; in others, chambers are enlarged, are excessively lobate, or are otherwise aberrantly shaped. Because there are many possible sources of stress for foraminifera in near-shore, variable salinity environments, it is not clear at present if the observed test abnormalities are evidence of oil pollution. As the study continues, processing of offshore samples will be completed and hydrocarbon contamination levels will be determined at selected sites.