We exposed a mesopelagic microbial community to three concentrations of Corexit 9500 and oil and analyzed microbial responses to treatments with oil, Corexit, or mixtures of these at different proportions. We used three concentrations of Corexit 9500 dispersant spanning three orders of magnitude, 0.2-20%, to characterize the chemical signatures of the chemically enhanced water accommodated fraction (CEWAF) and dispersant only mixtures and determine their effect on microbial community composition as assayed via 16S rRNA amplicon analysis.