Sub-lethal effects of chemically enhanced water accommodated fraction from marine gas oil on Calanus finmarchicus

The increased routine use of marine gas oils (MGO) has increased the risk of marine oil spills during its transport, use and disposal, threatening open ocean and coastal environments. One of the standard oil spill remediation methods is the application of chemical dispersants to break down surface oil slicks. Although previous studies have investigated the toxicity of MGO through its water accommodated fractions (WAF), few have examined how chemically enhanced WAF (CE-WAF) produced by the application of commercial dispersants, modifies the toxicity to marine organisms in cold environments. The copepod Calanus finmarchicus is an important component of the zooplankton community of the North Atlantic and an important dietary source of food for several commercially important fish species. C. finmarchicus has been extensively used in studies concerning hydrocarbon contamination, thus making it a suitable organism to investigate relevant environmental effects of the CE-WAF from MGO. Hence, the objective of this study was to investigate relevant sublethal effects of an MGO treated with the dispersant FinaSol OSR52 (10% of oil mass) on the defensome of C. finmarchicus. Adult C. finmarchicus were exposed under static conditions for 24, 48, 72 and 96 h to a sublethal concentration of CE-WAF corresponding to half of the calculated acute LC₅₀-value after 96 h. Sublethal effects were investigated by observing the transcription patterns of selected biomarker genes, activities of oxidative stress biomarker enzymes, levels of lipid peroxidation, and accumulation of the carotenoid astaxanthin in its free form. Gene transcription analysis showed significant downregulation of the biotransformation gene cyp 330A1 in all the exposed groups compared to controls, and changes in the transcription levels of genes such as elongase, fatty acid binding protein and ferritinThis suggest that exposure to CE-WAF affected lipid metabolism and consequently affected the ability of the copepods to store energy. A significant reduction in activities of the oxidative stress biomarker enzymes, such as Catalase, Superoxide dismutase and total Glutathione, suggests that exposure to the CE-WAF induced oxidative stress, likely through depletion or inhibition of the antioxidant defense system. However, no significant difference was observed among exposure and control groups regarding lipid peroxidation. Finally, the 24 h exposure affected the concentrations of the carotenoid astaxanthin in free form, suggesting that exposure affected the dynamics of the utilization of astaxanthin in the copepod.