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  • Writer's pictureAPECS Belgium

Polar Cod: a keystone species facing challenges with decreasing sea ice

The Arctic is changing rapidly, exemplified by elevating temperatures, a reduction in sea ice thickness and extent and changes in ocean pH and salinity. This year, the onset of the sea ice melt season probably started on the 13th of March when sea ice extent reached its maximum1. Since this maximum, sea ice extent is at record low levels. The latter and other climate-induced changes put an increasing pressure on the Arctic ecosystem and its populations, including the most abundant circumpolar marine fish polar cod (Boreogadus saida). Its adaptation to polar conditions and close association with sea ice is reflected by the production of antifreeze molecules that avoid growing of ice crystals in the blood and thus, allow this fish to live in icy conditions. As a keystone species, changes in its abundance, distribution and food resources will impact the entire Arctic ecosystem. Additionally, boreal marine fish, such as the economically important Atlantic cod and herring move poleward into unexploited parts of the Arctic. It remains uncertain how these boreal newcomers will affect interactions for polar cod and the Arctic marine food web. During my PhD, I apply next-generation sequencing methods on different geographical populations to improve the knowledge on polar cod’s population genomic structure and adaptation to its rapidly changing environment. Identifying genetically different populations, their connectivity and mapping the temporal and spatial distribution of polar cod over time is crucial for the conservation of this species.

Photo credit: Peter Leopold / Norwegian Polar Institute

1 The full analysis of this year’s ice conditions is available at National Snow and Ice Data Center (NSIDC) Arctic Sea Ice News & Analysis page ( Accessed 29 April 2019.

Written by Sarah Maes

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