The worldwide increasing recourse to chemical dispersants to deal with oil spills in marine coastal ecosystems is a controversial issue. Yet, there exists no adequate methodology that can provide reliable predictions of how oil and dispersant-treated oil can affect relevant organism or population-level performance. The primary objective of the present study was to examine and compare the effects of exposure to untreated oil (weathered Arabian light crude oil), chemically dispersed oil (Finasol, TOTAL-Fluides) or dispersant alone, upon the ability of fish for environmental adaptation. To reach that goal, we implemented high-throughput, non-lethal challenge tests to estimate individual hypoxia and heat tolerance as surrogate measures of their capacity to face natural contingencies. Experimental populations were then transferred into semi-natural tidal ponds and correlates of individuals' fitness (growth and survival) were monitored over a period of 6 months. In accordance with our stated objectives, the contamination conditions tested corresponded to those observed under an oil slick drifting in shallow waters. Our results revealed that the response of control fish to both challenges was variable among individuals and temporally stable (repeatable) over a 2-month period. Exposure to chemical dispersant did not affect the repeatability of fish performance. However, exposure to oil or to a mixture of oil plus dispersant affected the repeatability of individuals' responses to the experimental challenge tests. At population level, no difference between contamination treatments was observed in the distribution of individual responses to the hypoxia and temperature challenge tests. Moreover, no correlation between hypoxia tolerance and heat tolerance was noticed. During the field experiment, hypoxia tolerance and heat tolerance were found to be determinants of survivorship. Moreover, experimental groups exposed to oil or to dispersant-treated oil displayed significantly lower survival than control or dispersant-exposed groups. Finally, from the four experimental populations tested, the one exposed to chemically dispersed oil presented the lowest growth rate.
Human alteration of marine ecosystems is substantial and growing. Yet, no adequate methodology exists that provides reliable predictions of how environmental degradation will affect these ecosystems at a relevant level of biological organization. The primary objective of this study was to develop a methodology to evaluate a fish's capacity to face a well-established environmental challenge, an exposure to chemically dispersed oil, and characterize the long-term consequences. Therefore, we applied high-throughput, non-lethal challenge tests to assess hypoxia tolerance, temperature susceptibility and maximal swimming speed as proxies for a fish's functional integrity. These whole animal challenge tests were implemented before (1 month) and after (1 month) juvenile European sea bass (Dicentrarchus labrax) had been acutely exposed (48h) to a mixture containing 0.08gL(-1) of weathered Arabian light crude oil plus 4% dispersant (Corexit© EC9500A), a realistic exposure concentration during an oil spill. In addition, experimental populations were then transferred into semi-natural tidal mesocosm ponds and correlates of Darwinian fitness (growth and survival) were monitored over a period of 4 months. Our results revealed that fish acutely exposed to chemically dispersed oil remained impaired in terms of their hypoxia tolerance and swimming performance, but not in temperature susceptibility for 1 month post-exposure. Nevertheless, these functional impairments had no subsequent ecological consequences under mildly selective environmental conditions since growth and survival were not impacted during the mesocosm pond study. Furthermore, the earlier effects on fish performance were presumably temporary because re-testing the fish 10 months post-exposure revealed no significant residual effects on hypoxia tolerance, temperature susceptibility and maximal swimming speed. We propose that the functional proxies and correlates of Darwinian fitness used here provide a useful assessment tool for fish health in the marine environment.
Dispersants are often used after oil spills. To evaluate the environmental cost of this operation in nearshore habitats, the experimental approach conducted in this study exposed juvenile golden grey mullets (Liza aurata) for 48 h to chemically dispersed oil (simulating, in vivo, dispersant application), to dispersant alone in seawater (as an internal control of chemically dispersed oil), to mechanically dispersed oil (simulating, in vivo, natural dispersion), to the water-soluble fraction of oil (simulating, in vivo, an oil slick confinement response technique) and to seawater alone (control condition). Biomarkers such as fluorescence of biliary polycyclic aromatic hydrocarbon (PAH) metabolites, total glutathione liver content, EROD (7-ethoxy-resorufin-O-deethylase) activity, liver antioxidant enzyme activities, liver lipid peroxidation and an innate immune parameter (haemolytic activity of the alternative complement pathway) were measured to assess the toxicity of dispersant application. Significant responses of PAH metabolites and total glutathione content of liver to chemically dispersed oil were found, when compared to water-soluble fraction of oil. As was suggested in other studies, these results highlight that priority must be given to oil slick confinement instead of dispersant application. However, since the same patterns of biomarker responses were observed for both chemically and mechanically dispersed oil, the results also suggest that dispersant application is no more toxic than the natural dispersion occurring in nearshore areas (due to, e.g. waves). The results of this study must, nevertheless, be interpreted cautiously since other components of nearshore habitats must be considered to establish a framework for dispersant use in nearshore areas.
The in vitro effects of polycyclic aromatic hydrocarbons (PAHs) on haemocyte and haemolymphatic parameters of the Pacific oyster, Crassostrea gigas, were tested using field concentrations (10(-7) and 10(-9) mg mL(-1)) observed in the Marennes-Oleron Basin (Charente-Maritime, France) and high concentrations (10(-3) and 10(-5) mg mL(-1)) observed during oil spills. As a first step, the effects of pollutants, after a 24 h contamination period, were monitored on individual and pooled haemolymph samples and similar results were observed for both sample types. In a second step, haemolymphs from 45 oysters were withdrawn and pooled. Eighteen pollutants were tested in vitro after a 4 and 24h contamination period and 10 of them showed significant modulations of the five haemocyte parameters tested. Seven pollutants (fluorene, pyrene, anthracene, phenanthrene, chrysene, indeno[1,2,3-c,d]pyrene and heavy fuel oil (HFO)) induced a decrease in haemocyte mortality. Fluorene, pyrene and HFO significantly decreased phagocytosis activity. Percentage of non-specific esterase positive cells, phenoloxidase activity and lysosome presence were increased by naphthalene, benzo[b]fluoranthene and dibenz[a,h]anthracene, respectively. Modulation of immune parameters in the Pacific oyster by PAHs suggested that PAH pollution may be related to enhanced susceptibility to diseases.
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