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In the Arctic, melting sea ice forces polar bears to work harder to hunt seals. The warming climate also invites more southerly species such as grizzlies, salmon, red foxes, and killer whales to expand their ranges north. But what’s happening at the low end of the food web where plants and algae reside?

Increasing ocean temperatures will alter the diversity and range of marine life—from mammals to shellfish to fish to seaweed—in coastal Arctic waters.

A collaborative study, from the University of Algarve in Portugal, focused on the expansion of eelgrass and macroalgae, specifically intertidal and subtidal brown seaweed. Researchers looked at a variety of warming scenarios, including the worst case: Arctic temperatures rising 3.4 to 6.7 °C above the historical average this century, depending on the region.

Freezing temperatures and ice cover, which scours the nearshore ocean floor and blocks sunlight, normally constrain eelgrass and macroalgae in the Arctic. But melting sea ice and warming waters create favorable conditions for expanding the range of their habitat.

The modeling forecasts that at the warmest prediction, eelgrass and macroalgae will shift north by 20.8 kilometers per decade—a move of up to 1.5 degrees in latitude. Eelgrass and macroalgae could transform polar habitat, increasing their range by up to 123,360 square kilometers—or about one and a half times the size of Ireland—by the end of this century.

Graphic by Assis et al.

On the positive side, more eelgrass and macroalgae mean more atmospheric carbon storage. The presence of eelgrass and seaweed also reduces coastal erosion and increases biodiversity by providing foraging opportunities for geese and habitat for mussels, scallops, crabs, and juvenile cod.

The negative consequence is to the polar environment. The changes will create competition for native species and risk the “complete squeeze out of high Arctic ecosystems,” the study warns.