THE EFFECTS OF OIL FROM THE MACONDO BLOWOUT ON INFAUNAL FORAMINIFERA OF LOUISIANA AND MISSISSIPPI MARSHES

Heavy contamination by BP oil apparently affected infaunal marsh foraminifera by reducing both their standing stock and depth of habitation, but moderate to light oiling seemed to have little effect. Nine cores from marshes of Barataria Bay (La.) and the Mississippi Sound were examined before and after oiling by the Macondo well blowout of 2010. The sites were sampled at different times of the year by necessity. Cores were taken from the mid to lower marsh in the Spartina alterniflorazone and sliced at 1-cm intervals to 10 cm depth in core. Samples stained with rose Bengal were washed on a screen with 45-µm openings to capture juvenile and small adult specimens, and were then split using a settling-type splitter. Slices were counted downcore until 95% of stained specimens were accumulated (defined as the depth of habitation). Specimens were kept wet throughout processing. The degree of oiling was assigned from the shoreline cleanup assessment technique (SCAT) data published by the environmental response management application (ERMA), and subsequently the concentration of polycyclic aromatic hydrocarbons (PAH) was measured in the cores.

Arenoparrella mexicana or Ammotium salsum and Miliammina fusca dominate the assemblages from the Mississippi Sound and include about a dozen ancillary species. Ammotium salsum dominates the low-lying marshes of Barataria Bay, with minor occurrence of several ancillary species. Assemblages seemed most affected by elevation in the marsh, season, salinity, and sediment composition, but not clearly by degree of oiling. In contrast, heavy oiling appears to affect the depth of habitation and standing stock (in 10 cm² integrated over the depth of a habitation). Uncontaminated sites and sites lightly or moderately contaminated by Macondo oil had a depth of habitation deeper than 7 cm with most exceeding 10 cm. The standing stock of live specimens exceeded 1,000 specimens, ranging from 1,200 to 6,700, often with a subsurface maximum. In contrast, at heavily oiled Bay Jimmy, the depth of habitation was only 2-3 cm, and the standing stock was 400-800 live specimens with most living in the top centimeter. The Bay Jimmy cores contained deformed specimens, which were not observed elsewhere. The shallow distribution of live specimens at Bay Jimmy has implications for marsh functioning.