Abstract:

Examine the priming effect hypothesis through mesocosm experiments and its implications for planktonic food web and fisheries production. The sustained low DOC concentrations below pre-spill concentrations may be due to primordialization of the food web, increased bioavailability of labile C sources promoting microbial diversity and cell activity, thus increasing humics/high fractionated oil components related to dead zones. The Deepwater Horizon (DwH) oil spill was unprecedented in the magnitude and extent of oil released into the water column. Regular two-week monitoring by the Fisheries Oceanography of Coastal Alabama (FOCAL) program as part of GRI funding, documented marked changes in labile carbon (C) pools, and in microbial and zooplanktonic processes in response to the presence of oil in coastal waters of Alabama. In particular, isotopically light C signatures in the micro-and meso-zooplankton fractions suggest that oil-derived C entered the planktonic food web on short time-scales, and that this shift was likely mediated by microbial metabolic processes. However, dissolved organic C (DOC) stocks remained very low (<100µM) compared to historical pre-spill conditions (typically >150µM), despite huge amounts of oil-derived C and high freshwater (humic) inputs into coastal waters. One possible explanation for sustained low DOC concentrations is primordialization of the food web in which increased bioavailability of labile C sources will promote microbial diversity and cell activity, which in turn will stimulate high update of refractory DOM (e.g., humics, high fractionated components of crude oil). Assuming this effect occurred during the DwH oil spill, there are important implications of the priming effe ct for ecosystem functioning, including increased C bioavailability for planktonic food webs from both oil- and refractory/freshwater organic sources, which has consequences for fisheries production. In this project, we expanded our knowledge base and specifically examine the priming effect hypothesis and its implications for planktonic food web processes and fisheries production. We conducted a series of controlled mesocosm experiments in June and August 2011 using radio- and stable-isotopes, chromophoric dissolved organic matter (CDOM) spectra and other oceanographic techniques to measure microbial metabolism of oil (labile) and humic (refractory) material under various conditions and also how changes in microbial processes relates to changes in planktonic food webs. Experimental results will be compared to a six-years of historical baseline information generated by FOCAL to evaluate the relative interannual and seasonal variability of the priming effect under pre- and post-spill conditions. Statistical analyses will include Parallel Factor Analyses (PARAFAC), in which the main environmental variables driving changes in DCOM pools will be modeled. The major implication of our study is that it will allow us to observe and understand source-sink dynamics of oil and dispersant and how this relates to microbial and planktonic food web processes. In addition, results from this study may be used as a model for other aquatic systems exhibiting similar changes in ecosystem baselines. To this end, we have also developed a global database of oil spills to evaluate the magnitude and extent of oil-derived carbon as it relates to other food web processes on global and regional scales, such as primary production, community respiration and how it relates to distribution of dead zones, and inputs of allochthonous organic material (e.g., terrestrial DOM).