Predicting Winners and Losers in a Warming Arctic

By the end of this century, Arctic ocean bottom temperatures may be too warm for most seafloor-dwelling invertebrates that currently reside there, a new study finds. Potential "losers" include snails, mussels, and other animals that are important prey for valuable commercial fish species and marine mammals such as endangered Pacific walrus. Arctic coastal communities also depend heavily on the arctic marine ecosystem for subsistence.

Snails, mussels, crabs, and sea stars are among the invertebrates that live on the arctic seafloor. Credit: NOAA Fisheries

NOAA Fisheries is working with our partners to understand how climate change is transforming arctic marine ecosystems. Our goal is to help the fisheries and communities that are part of them to prepare for the future. This new collaborative study is the first to look at climate change impacts on the entire suite of arctic seafloor invertebrates. An international team of scientists combined biological and climatological data to project how the thermal habitat available to these animals could change over time.

"Our models predict major changes in the seafloor invertebrate fauna that could reverberate through the whole arctic food web," said study leader Libby Logerwell, NOAA Fisheries Alaska Fisheries Science Center. "If warming continues, it is potentially going to make it very difficult for a lot of invertebrates to live there-and for the birds, mammals and humans that rely on them."

Map of the Bering and Chukchi Sea study area showing prevailing currents and some western Alaska coastal communities.

Partnerships Combine Capabilities to Predict Ecosystem Change

The research was a collaborative effort that brought together the biological and climatological expertise needed to understand ecosystem change in the Arctic. Research partners included:

• NOAA Fisheries Alaska Fisheries Science Center
• NOAA Research's Pacific Marine Environmental Laboratory
• University of Washington
• Institute of Marine Research in Norway

"I learned so much working with Pacific Marine Environmental Laboratory's Muyin Wang. I'm a biologist; she's an atmospheric scientist and climatologist," Logerwell said. "It was exciting to find out that you could project warming so far. It was sobering to see how much warming is predicted."

"I was really excited when Libby talked to me about starting this project together," Wang said. "As a climate scientist, I am also interested in how the changing Arctic climate would impact the components of the ecosystem. This project demonstrated a powerful tool we have to examine that-climate model projections at regional scales."

Past Surveys Help Forecast the Future

The predictions were based on a decade (2009-2018) of existing data from Alaska Fisheries Science Center fish surveys in the Bering and Chukchi seas. The team analysed invertebrate catch and bottom temperature data to determine the "preferred" temperature for different animals. They categorized species into warm and cold water groups. Using eight climate models, they projected mean increases in summer bottom temperature to years 2050 and 2100. Based on these projections, they looked at how availability of thermal habitat for warm and cold water invertebrate groups might change with ocean warming.

"This is one of the first times anyone has analyzed invertebrate data from these surveys in this way. When they started the surveys, they weren't focusing on most of these invertebrates, just fish and crab. But the data are there," Logerwell said. "The long time series of survey data contains a wealth of information. We were able to use some of that to make these predictions."

NOAA Fisheries scientist Alex Andrews and Libby Logerwell sort a sample of seafloor invertebrates during an Alaska Fisheries Science Center survey. Credit: NOAA Fisheries.

Rising Temperatures Decide Future Winners and Losers

The climate models predict that the Bering and Chukchi seas will heat rapidly if we remain on the current climate change trajectory. Average summer bottom temperature over the entire region is projected to rise by 2.3°F by mid-century, and 8.1°F by the end of the century.

Under this "business-as-usual" climate change scenario, thermal habitat for all but the few most heat-tolerant arctic invertebrates is projected to shrink dramatically northward.

The "losers"-cold water species-would lose 50 percent of their thermal habitat by mid-century. By the end of the century, habitat for these animals would be virtually gone. Only 2 percent of the entire Bering and Chukchi sea region would be within their temperature range.

The "winners" included only a few arctic invertebrates that can tolerate a wide range of temperatures. By 2100 this group is projected to have suitable thermal habitat throughout most of the Bering and Chukchi Seas, except nearshore coastal regions.

The study did not examine whether more southerly invertebrates might expand north into a warming Bering Sea.

"The shallow depth of the Bering Sea shelf compared to their habitat to the south might make it unsuitable for southern species," Logerwell said. "The Bering shelf break and slope may act as a barrier to new species coming north."

"The magnitude of warming and habitat loss we projected was beyond anything I imagined," Logerwell said. "It's alarming to see how rapidly things will change, particularly in the last half of the century, if warming continues on the current trajectory."

Maps of average July-August bottom temperature forecasts: present (2008-2017), mid-century (2045-2054), and end of century (2091-2100).

Changes to Seafloor Fauna Reverberate Through the Food Web

The most abundant animals among the losers were snails and mussels. They are among the most frequently eaten prey of commercially valuable fish such as yellowfin sole, Alaska plaice and Pacific halibut. They are also prey for endangered Pacific walrus, which are harvested as a food resource by many native Alaskan communities.

A walrus on Bering Sea ice. Credit: NOAA Fisheries

The main winner was the basket star, a plankton-eating relative of seastars. Basket stars have little nutritional value, and likely few predators. Other potential winners included shrimp, barnacles, sea anemones, and brittle stars.

Besides potentially dire effects on the arctic food web, warming could drastically diminish arctic species diversity. By the end of the century, most of the region south of the Arctic Circle may only be suitable thermal habitat for the winners.

Logerwell stresses the importance of continued monitoring to track changes and refine predictions about the future of arctic seafloor invertebrates and their predators.

"Long time series are the best tool we have to detect climate impacts and predict future change," Logerwell said. "Our research contributes to NOAA Fisheries' ecosystem approach to management. The more we understand what may be coming, the better we can help fisheries and communities to be ready."

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