Cardiotoxic Effects from the Water-Soluble Fraction of Crude Oil on an Arctic Keystone Species – Polar Cod (Boreogadus saida)

Abstract

The Arctic ecosystems and its species are under increased anthropogenic pressure from both climate change and industrial activities. Of special interest is pollution from petrogenic substances, and in particular accidental oil spills, that pose a risk to arctic marine organisms. An oil spill in the Arctic may see crude oil encapsulated into the sea ice and over time leaching to surface waters in the vicinity. For all sympagic species this is a threat, and for polar cod (Boreogadus saida) with buoyant eggs aggregating in surface waters it is of imminent importance to understand how they are affected. A wide range of early life stages of marine fish have shown sensitivity to exposure from the WSF of crude oil, including polar cod. The effects from exposure involves symptoms like pericardial edema, yolk-sac alterations, malformations, bradycardia and arrhythmia. Polar cod is a keystone species in the Arctic pelagic ecosystem. The species feeds upon smaller zooplankton and is very effective at assimilating this energy into reproduction and growth, and thus funnels energy from lower trophic levels all the way up to marine mammals and seabirds. We exposed buoyant polar cod eggs to environmentally realistic concentrations of the water-soluble fraction (WSF) of crude oil through an oiled rock column experiment over 79 days. The experiment mimicked a potential spill in the Arctic exposing the buoyant polar cod eggs to a continuous release of water-soluble oil components from the sea ice. The total amount of the polycyclic aromatic hydrocarbons (sum of 44 PAHs) in the water were in the ng/L range and the highest concentration measured in eggs were roughly at 1100 ng/g wet weight. In addition to crude oil exposure. The embryos were maintained under two different temperature regimes, 0 °C and 3 °C respectively to determine if additional pressure from elevated temperatures could affect the severity of toxicity. This is the first study to document dose dependent effects in cardiotoxicity for an arctic keystone species, but also underlines previously observed effects regarding toxicity from the WSF of crude oil in early life stages of marine fish (e.g. yolk-sac alterations, pericardial edema, deformities, increased mortality etc.). The study couldn’t observe a clear increased toxicity between temperature regimes, but it’s is not ruled out as a potential stressor for polar cod and the Arctic system in general. Thus, further research is needed to understand how temperature effects polar cod embryos in general and specifically when exposed to additional stressors. Effects from very low environmentally realistic concentrations of the WSF of crude oil seen in this study may have implications for the arctic keystone species – polar cod. This short-lived species whom invests large amounts of its energy into reproduction may have impaired recruitment due to oil spills and pollution and thus, it most likely will affect food web dynamics and the Arctic system as a whole.