Sublethal Effects of Crude Oil and Chemical Dispersants on Multiple Life History Stages of the Eastern Oyster, Crassostrea virginica

Brad J. Gemmell,Kevin T. Du Clos,Sara M. Garcia,Olivia H. Hawkins

doi:10.3390/jmse8100808

Brad J. Gemmell, Kevin T. Du Clos + Show 2 more

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https://doi.org/10.3390/jmse8100808

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Abstract

The eastern oyster Crassostrea virginica is an ecologically and economically important species that is vulnerable to oil pollution. We assessed sublethal effects of soluble fractions of crude oil alone (WAF) and crude oil in combination with Corexit 9500 dispersant (CEWAF) on oysters at three life history stages. Veliger swimming, pediveliger settlement, and adult clearance rates were quantified after 24 h exposures to the contaminants. Veliger swimming speeds were not significantly impacted by 24 h exposures to WAF or CEWAF. A larger proportion of veligers were inactive following WAF and CEWAF exposure as compared to the control, but the effect was greater for pediveligers, and pediveliger settlement in the highest concentration CEWAF treatment decreased by 50% compared to controls. Thus, pediveligers may be particularly vulnerable to oil exposure. In the adults, we found significant clearance rates reductions that persisted 33 days after acute exposure to CEWAF. Knowledge of sublethal effects of oil and dispersant at multiple life history stages aids understanding of how this important species will respond to an oil spill.

Highlights

Offshore oil spills, such as the Deepwater Horizon (DWH) spill that occurred from 20 April to 15 July of 2010 in the Gulf of Mexico, have wide ranging impacts
Oyster veligers appeared to be quite resistant to acute exposure of soluble fractions of crude oil and chemical dispersant, as we found no significant differences in swimming behavior (Figure 1)
Decreased settlement has been observed in pediveligers when exposed to water accommodated fractions (WAF) and chemically enhanced water accommodated fractions (CEWAF) for 72 h [16], but here we show that negative effects can occur at lower concentrations and shorter exposure durations

Summary

Introduction

Offshore oil spills, such as the Deepwater Horizon (DWH) spill that occurred from 20 April to 15 July of 2010 in the Gulf of Mexico, have wide ranging impacts. During the DWH spill, an estimated 7.2 × 106 L of chemical dispersants (Corexit 9500 and Corexit 9527) was employed as traditional surface applications as well as 2 × 106 L subsurface at the well-head [1,3] These powerful surfactants alter the chemical and physical components of oil, reducing the surface tension between oil and water, and allow the oil to be emulsified and dispersed in the water column more with sufficient wave energy [4]. While these methods enhance the effectiveness of oil dispersal, they increase the persistence of soluble crude oil fractions, such as polycyclic aromatic hydrocarbons (PAHs), in the water column [5,6]. The small droplets are unable to re-coalesce, increasing interactions of microdroplets with planktonic organisms or sessile organisms that feed on small particulates [1]

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