Seasonal Monitoring of Hydrocarbon Degraders in Alabama Marine Ecosystems Following the Deepwater Horizon Oil Spill Agota Horel & Behzad Mortazavi & Patricia A. Sobecky Received: 10 October 2011 / Accepted: 31 January 2012 / Published online: 29 February 2012 # Springer Science+Business Media B.V. 2012 Abstract Following the Deepwater Horizon explo- sion and crude oil contamination of a marsh ecosystem in AL in June 2010, hydrocarbon-degrader microbial abundances of aerobic alkane, total hydrocarbon, and polycyclic aromatic hydrocarbon (PAH) degraders were enumerated seasonally. Surface sediment sam- ples were collected in October and December of 2010 and in April and July of 2011 along 40–70-m transects from the high tide to the intertidal zone including Spar- tina alterniflora-vegetated marsh, seagrass (Ruppia maritima)-dominated sediments, and nonvegetated sediments. Alkane and total hydrocarbon degraders in the sediment were detected, while PAH degraders were below detection limit at all locations examined during the sampling periods. The highest counts for microbial alkane degraders were observed at the high tide line in April and averaged to 8.65×10 5 of cells/g dry weight (dw) sediment. The abundance of alkane degraders dur- ing other months ranged from 9.49×10 3 to 3.87×10 4 , while for total hydrocarbon degraders, it ranged be- tween 5.62×10 3 and 1.14×10 5 of cells/g dw sediment. Pore water nutrient concentrations (NH 4 + , NO 3 - , NO 2 - , and PO 4 3- ) showed seasonal changes with minimum values observed in December and April and maximum values in October and July. Concentrations of total petroleum hydrocarbons in sediments averaged 100.4± 52.4 and 141.9±57.5 mg/kg in January and July, 2011, respectively. The presence of aerobic microbial commu- nities during all seasons in these nearshore ecosystems suggests that an active and resident microbial commu- nity is capable of mineralizing a fraction of petroleum hydrocarbons. Keywords Deepwater Horizon . Crude oil . Hydrocarbon degraders . Macondo well . Biodegradation . Salt marsh 1 Introduction On April 21, 2010, the Deepwater Horizon oil rig explosion caused the release of approximately 4.4× 10 6 barrels (7.0×10 5 m 3 , ±20%) of crude oil into the Gulf of Mexico during an 84-day period (Crone and Tolstoy 2010). A large fraction of the released oil underwent rapid biodegradation at depth in the deep sea (Hazen et al. 2010; Azwell et al. 2011), but some of the oil released into the water column reached the Northern Gulf of Mexico (NGM) shorelines and contaminated beaches and salt marshes. Water Air Soil Pollut (2012) 223:3145–3154 DOI 10.1007/s11270-012-1097-5 Electronic supplementary material The online version of this article (doi:10.1007/s11270-012-1097-5) contains supplementary material, which is available to authorized users. A. Horel : B. Mortazavi : P. A. Sobecky Department of Biological Sciences, University of Alabama, PO Box 870344, Tuscaloosa, AL 35487, USA A. Horel (*) : B. Mortazavi Dauphin Island Sea Lab, 101 Bienville Blvd, Dauphin Island, AL 36528, USA e-mail: ahorel@ua.edu