Entry for:The Peer Prize for Climate
Climate change is driving the redistribution of marine species in the Arctic. Two sub-Arctic fishes, capelin (Mallotus villosus) and sandlance (Ammodytes spp.), have expanded their habitats polewards and are replacing Arctic cod (Boreogadus saida) as the main prey for Arctic piscivores. These changes are more pronounced in lower to mid-Arctic latitudes, where capelin and sandlance are abundant and Arctic cod is becoming scarce. Sub-Arctic fishes could act as contaminant vectors into Arctic food-webs due to their more southern distribution. To understand the effects of these movements, we compared levels of anthropogenic contaminants in sub-Arctic and Arctic native prey species.
This study included Arctic species that are common prey for Arctic piscivores: amphipods (Amphipoda), sculpin (Cottoidea), northern shrimp (Pandalus borealis), Arctic cod, and the sub-Arctic capelin and sandlance. We sampled amphipods, sculpin and Arctic cod in different latitudinal regions representing the low, mid- and high Arctic, to consider regional variation in the composition of the Arctic prey community.
Gas chromatography was used to quantify levels of legacy organic contaminants: polychlorinated biphenyls (PCBs, used e.g. as stabilizers of electrical devices), several organochlorine pesticides (OCs, such as DDT, largely used in agriculture) and brominated flame retardants (such as PBDEs, used to delay fires in home/industrial materials). These contaminants were banned by the Stockholm Convention but persist in the environment at relatively high levels. Absorption spectrometry was used to quantify total mercury (THg, released for example as a by-product of fossil fuel combustion).
We additionally measured ecological tracers of habitat used (carbon stable isotopes) and trophic position (nitrogen stable isotopes), and fish length. These ecological and biological variables were used to try to explain the contaminant variation among species.
Up to four times higher levels of THg, PCBs and OCs were found in Arctic natives sculpin and northern shrimp compared to other fishes. These results may be due to the relatively more benthic feeding habits of sculpin and northern shrimp and their higher trophic positions. These factors are normally associated with higher contaminant levels due to accumulation of contaminants in the bottom/nearshore of the marine environment and biomagnification along the food-web. In terms of regional variation, there was no clear latitudinal trend for the species studied.
When comparing Arctic cod to its sub-Arctic ‘replacements’, capelin had up to two times higher levels of most organic contaminants, whereas sand lance had more intermediate levels between the two. Conversely, Arctic cod had higher levels of mercury than capelin. Differences in organic contaminant levels were not explained by biological and ecological variables. Instead, capelin contaminant signatures suggest migratory habits. In other words, higher proportions of the heavier/less volatile contaminants suggest that capelin migrate to more southern regions, at least a part of the year, where it picks up more contaminants.
A dietary shift from Arctic cod to capelin and/or sand lance may only have a weak influence on Arctic piscivore’s exposures to THg and organic contaminants since these differences were only up to two-fold and other natives had higher contaminant burdens. Nevertheless, this study shows that sub-Arctic species can bring more contaminants to Arctic food webs. It is thus critical to understand the effects of the climate change-driven re-restructuring of marine food-webs, especially in Arctic regions where temperatures are increasing twice as fast as the world average.
5. Future ideas/collaborators needed to further research?
A change in diet may not only be associated with a change in contaminant exposure, but also to a shift in nutritional value. For example, Arctic fish tend to have high lipid content, as an adaptation to low temperatures. If capelin and sand lance represent prey of lower nutrient content, coupled with higher levels of certain contaminants, then the impact of these prey fish community changes may be a greater concern for Arctic piscivores. Thus, further work will focus on quantifying important nutrients, such as essential fatty acids and selenium.