Oil spills could harm the Arctic more than expected

The Arctic sea ice is melting due to climate change. This creates an increased interest in exploring the oil resources in the area. But how will oil spills from, e.g., oil drilling or tankers affect the Arctic ecosystem?

New research published by DTU Aqua and COWI in the highly respected American journal Environmental Science and Technology shows that an oil spill – in this case in the winter – can have more serious consequences for food chains in the Arctic than previously assumed.

“The most surprising finding is that it takes a lot less of the toxic substance pyrene from crude oil to kill zooplankton than we have seen in previous experiments. At doses 300 times smaller than what we have seen so far, half of the copepod species Calanus glacialis in our experiment died,” says PhD Kirstine Toxværd, who finalized her PhD on the topic recently.

One of the explanations for the new findings is that the researchers exposed the copepods to pyrene for a longer period of time. Previous studies have only lasted a few weeks, but that is insufficient if you want to mimic oil spill conditions.

Copepods are very important organisms in marine food chains. They graze phytoplankton and make up a significant part of the diet for fish, birds, and marine mammals. Changes in the copepod biomass may therefore affect the entire food chain and ultimately affect fish stock and thereby income for Arctic communities.

Oil spills affect survival and reproduction

Like most animals in the Arctic, the copepods hibernate during the long, dark winter. They spend the winters close to the seabed living off their fat deposits, but once the sun boost the growth of phytoplankton in the surface, they swim up to eat the algae and then they grow and reproduce and make up the food basis for the rest of the food chain.

In the laboratory, researchers reproduced the life cycle of the two main copepods in the Arctic – Calanus glacialis and Calanus hyperboreus – and subjected them to different doses of pyrene for three months during the copepod winter break. The pyrene doses used corresponded to actual doses that may occur in an oil spill in nature. The copepods were then transferred to clean water and were fed for a month to imitate the spring phytoplankton bloom.

Calanus glacialis was most affected by the oil spill and did not fully utilize its fat deposits as well as having a higher mortality rate during the winter when exposed to pyrene – and the more pyrene, the greater the effect. Furthermore, researchers recorded negative effects on the copepods’ ability to eat and rebuild fat deposits and produce eggs when they were fed again.

“These new findings are an important contribution to the assessment of the possible effects of oil spills on Arctic ecosystems and should be included in authority risk assessments,” says Professor Torkel Gissel Nielsen, DTU Aqua, who spearheaded the project.

According to the results of the experiments, the second copepod species, Calanus hyperboreus, was also affected by the pyrene, but not quite as much as Calanus glacialis. The overwintering copepods of this species did not immediately die from being exposed to pyrene, and the production of eggs was not affected either. However, they ate less and their abilities to rebuild their fat deposits when feed again deteriorated, which reduces the likelihood that they will survive the next winter

(Karin Stubgaard)