The response of marine bacteria to Corexit 9527, with and without Prudhoe Bay crude oil labeled withn-(1-(14)C)hexadecane, in a temperate pelagic environment was monitored over 22 days using controlled ecosystem enclosures. The results indicated that Corexit and Corexit-dispersed crude oil stimulated bacterial production by serving as substrates and/or by inducing the release of organic compounds from the indigenous phytoplankton population. Highest bacterial standing stock was observed in the enclosure treated with a mixture of Corexit and crude oil, in which a large fraction of the predominant bacterivores were eliminated. Biodegradation appeared to be more significant than abiotic processes in contributing to the loss of low volatility n-alkanes in Corexit-dispersed oil. Twenty-two days following its addition, 50% of the radiotracer was recovered: 3% in the suspended particulate fraction, 10% in sedimentary material, 36% as CO2, and less than 1% in the dissolved organic pool.