Effects of crude oil, chemical dispersant, and UV radiation on copepod nauplii from the Gulf of Mexico
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Anthropogenic oil spills continue to have devastating effects on the ecosystems in which they occur. Understanding how marine ecosystems are affected by these events is important for future mitigation and the improvement of preventative and restoration methods. The goal of this study was to investigate how copepods, the predominant group of zooplankton and base of the marine food web, respond under oil spill conditions. Two important and novel aspects were included: (1) exposing copepods at an early life stage when individuals tend to be more vulnerable to contaminant exposure and (2) including UV radiation as a factor in toxicity analysis. Three species of copepod nauplii, native to the Gulf of Mexico, were exposed to concentrations of crude oil (0.5-2 µL/L) and chemical dispersant (0.5 µL/L) for 48 hours. Survival, growth, and swimming behavior of the copepod nauplii were examined. At relatively low concentrations of oil (≥1 µL/L) sublethal effects were observed, including changes in growth and swimming behavior. Most notably, oil (1 µL/L) + dispersant, in the presence of UV caused a significant increase in mortality by 8X and oil (2 µL/L) in the presence of UV caused a significant increase in mortality by 13X, compared to the controls. A LC50 of 2.0 µL/L of crude oil was observed without UV exposure and a LC50 of 1.3 µL/L of crude oil was observed in the presence of UV. These results demonstrate the importance of considering factors such as UV exposure, chemical dispersant, and life stage when evaluating the potential toxicity of an oil spill to marine organisms.