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

Rf Peiffer,Jh Cohen

doi:10.3354/ab00625

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 Mne- miopsis 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 glutathione- s-transferase (GST) activity were conducted on individuals surviving 24 h exposures to test solu- tions at both 15 and 23°C. GST activity increased significantly in 2.5 and 5 mg l �1 dispersant solu- tions 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 emis- sion 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.

Highlights

Accidental offshore oil releases have highlighted the need to better understand oil and chemical dispersant effects on pelagic organisms (Thibodeaux et al 2011, Barron 2012)
The present study examined lethal levels of exposure for a mid-Atlantic population of the ctenophore M. leidyi at 2 seasonally relevant temperatures upon acute exposure to Corexit 9500A dispersant, crude oil (WAF), and dispersed crude oil (CEWAF) to set exposure levels for sublethal experiments
A difference between 24 and 48 h LC50s was observed for CEWAF mortality based on total petroleum hydrocarbon (TPH) concentration but not on nominal loading concentration (Table 1)

Summary

INTRODUCTION

Accidental offshore oil releases have highlighted the need to better understand oil and chemical dispersant effects on pelagic organisms (Thibodeaux et al 2011, Barron 2012). Dispersants are often employed to degrade surface slicks in the interest of protecting shorelines, but their use increases exposure of pelagic organisms by allowing oil at the ocean surface to mix into the water column inhabited by these organisms (Reed et al 2004) Both lethal and sublethal toxicological data are limited for crude oil, dispersed oil, and dispersant itself across a range of ecologically important and abundant. Almeda et al (2013a) exposed several species of gelatinous zooplankters to crude oil emulsions Their results suggest that gelatinous zooplankters, coastal ctenophores, have the potential to be vectors of hydrocarbons up pelagic food webs, as these organisms survive oil exposures better than most zooplankton and accumulate high-molecularweight polycyclic aromatic hydrocarbons (PAHs). Subsequent sublethal exposure studies examining parameters that may change over acute exposure time frames determined ctenophore respiration rate and capacity for bioluminescence, as well as activity of the detoxification enzyme GST in ctenophore tissue

MATERIALS AND METHODS

RESULTS

DISCUSSION