Lethal and sublethal effects of oil, chemical dispersant, and dispersed oil on the ctenophore Mnemiopsis leidyi

Abstract

We established the lethal levels for water-accommodated fractions of Corexit® 9500A chemical dispersant, crude oil (WAF), and dispersed crude oil (CEWAF) for the ctenophore Mnemiopsis leidyi at both 15 and 23°C. This gelatinous zooplankter was sensitive to dispersant at both temperatures, as well as to oil solutions, with some increase in toxicity of CEWAF as compared to WAF. Subsequent sublethal assays for routine respiration rate, bioluminescence, and glutathiones- transferase (GST) activity were conducted on individuals surviving 24 h exposures to test solutions at both 15 and 23°C. GST activity increased significantly in 2.5 and 5 mg l-1 dispersant solutions at 15°C, suggesting a metabolic detoxification response to the dispersant-containing solutions, but no effect of any solution type on routine respiration rate was observed. Light emission through mechanically stimulated bioluminescence and photocyte lysis decreased with exposure to crude oil WAF and CEWAF at both temperatures and to dispersant exposure at 23°C. Collectively, these results demonstrate that M. leidyi exhibits both lethal and sublethal effects from acute crude oil exposure, with an elevation of some sublethal responses upon addition of chemical dispersant. Sublethal effects of oil and dispersants in pelagic species, most notably impairment of luminescence, should be considered when evaluating oil spill response strategies.