Combined effects of salinity, temperature, hypoxia, and Deepwater Horizon oil on Fundulus grandis larvae.

Oil spills have polluted the marine environment for decades and continue to be a major source of polycyclic aromatic hydrocarbons (PAHs) to marine ecosystems around the globe, for example during the 2010 Deepwater Horizon spill. Although the toxicity of PAHs to fish has been well studied, their effects combined with abiotic stressors are poorly understood. The goal of this study was to describe the combined impacts of crude oil and environmental stressors on fish larvae, a sensitive life stage. Gulf killifish (Fundulus grandis) larvae (<24 h post-hatch) were exposed for 48 h to high energy water accommodated fractions (HEWAF; total PAHs 0-125 ppb) of Macondo oil from the Deepwater Horizon spill under different combinations of environmental conditions (dissolved oxygen 2, 6 ppm; temperature 20, 25, 30 °C; salinity 3, 10, 30 ppt). Even under optimal environmental conditions (25 °C, 10 ppt, 6 ppm) larval survival and development were negatively affected by PAHs, starting with the lowest concentration tested (∼15 ppb). Hypoxia and high temperature each increased the adverse effects of HEWAF on development and mortality. In contrast, salinity had little effect on any of the endpoints measured. Importantly, expression of the detoxifying gene cyp1a was highly induced in PAH-exposed larvae under normoxic conditions, but not under hypoxic conditions, potentially explaining the enhanced toxicity observed under hypoxia. This work highlights the importance of considering how suboptimal environmental conditions can exacerbate the effects of pollution on fish early life stages.