Longitudinal Assessment of Shifting Microbial Community Composition in Sandy Beaches Following the 2010 Deepwater Horizon Oil Spill and Remediation Efforts

Abstract

Sandy beaches are geological zones parallel to the shoreline where high energy, open ocean unconsolidated sediments are deposited and reworked. Sandy beaches represent critical ecosystems that support a wide variety of underappreciated biodiversity. Prior to the 2010 Deepwater Horizon oil spill in the Gulf of Mexico, the diversity and function of microbial communities in supratidal beach sediments along the Gulf of Mexico coastlines were not well understood. It was unclear if possible community compositional changes would occur during and following exposure to oil, or what impact the remediation efforts, such as sand washing, would have to the microbial communities and overall beach ecosystems. In this study, sites were chosen in late April and early May 2010 based on NOAA trajectory maps to determine where and when weathered oil would arrive on coastlines. Supratidal to subtidal transects perpendicular to the shoreline were sampled at the public beaches of Grand Isle, LA, and Dauphin Island, AL, over a year, including before the oil came ashore. Microbial diversity was assessed from analyses of 454 pyrosequences 16S rRNA genes, and changes in diversity was statistically analyzed in conjunction with environmental variables including grain size, organic carbon and water content, and pore water pH. Pre-oil samples from both sites provided information about the undisturbed microbial community composition while, post-oil spill samples provided information about changes in community composition impacted by abiotic and biotic factors. Statistical analysis for both sites showed significant shifts in microbial community composition that could be linked to changing sediment grain size and associated environmental variables like organic carbon and water content, and pH; over time, predominately from where remediation efforts were the greatest to clean the beaches after an oil spill were the most extensive, such as from sand washing. This research provides important annual information about changes in microbial community composition from sandy beaches, and demonstrates that remediation efforts to clean beaches after an oil spill may shift microbial community composition from what the earlier diversity might have been. The impact of remediation should be considered for future beach cleanup efforts.