LONGITUDINAL ASSESSMENT OF SHIFTING MICROBIAL COMMUNITY COMPOSITION IN SANDY BEACHES FOLLOWING THE 2010 DEEPWATER HORIZON OIL SPILL AND REMEDIATION EFFORTS

Sandy beaches are geological zones that parallel the shoreline where high energy, open ocean unconsolidated sediments are deposited and reworked. Sandy beaches represent a critical part of coastal ecosystems, whereby microbes serve as the base of beach food webs, acting as primary degraders of organic matter sourced from phytoplankton, stranded algae and plants, exudates, and carrion. The influx of these organics to supratidal zones, however, is generally limited. Prior to mid-2010 when the Deepwater Horizon oil spill occurred in the Gulf of Mexico (GoM), scant research had been done to appreciate the diversity and function of supratidal beach microbial communities. It was unclear what possible diversity and functional changes to the microbial communities would occur during and following exposure to oil, or what impact the potential changes would have to the overall beach ecosystem. In this study, sites were chosen late April-early May 2010 based on NOAA trajectory maps for where and when weathered oil would arrive on coastlines. Dauphin Island, AL, was sampled twice before weathered oil came ashore in May, and four times since. Grand Isle, LA, was sampled twice before oil washed ashore in May, and three times since. At both beaches, supratidal to subtidal transects perpendicular to the shore included background (non-oiled) sites, as well as oiled sites, and sites that were sand washed or left undisturbed. Samples were subjected to 454 tag pyrosequencing of 16S rRNA genes, and sequence analyses were done in conjunction with pore water pH and solute content measurements, as well as organic carbon content and grain size. Pre-oil samples from both beaches had low biomass, and were dominated by Proteobacteria, Firmicutes, Planctomycetes, and Chloroflexi phyla. Overall diversity increased for these sites, and post-oil samples had greater diversity of Proteobacteria, Spirochetes, and Bacteriodetes. An interesting result was that soil washed sites showed a decrease in biomass and diversity, represented by almost exclusively Proteobacteria and Firmicutes. This research provides important annual information about sandy beach microbial communities when exposed to oil, but also demonstrates that there are natural changes in microbial communities throughout the year that could not be attributed to oil exposure.