Out on Izembek Lagoon, the water was flat and clear. Alison Williams, a biologist with the U.S. Fish & Wildlife Service, dipped her paddle in and steered her kayak toward the center of the lagoon, where the seagrass below runs thick.

“Everything below us is eelgrass,” she said. “It actually evolved on land and then evolved to go back into the water.”

The lagoon is the heart of the Izembek National Wildlife Refuge, a wide expanse of tundra and small lakes that stretches 310,000 acres across the Alaska peninsula, between the Pacific Ocean and the Bering Sea. It’s the smallest federal wildlife refuge in Alaska but one of the most important. It’s home to hundreds of thousands of birds: Pacific black brant, emperor geese, pintails and eiders.

This time of year, Izembek is famous as a stopover for migrating birds — a place to rest and refuel as hundreds of species move between their southern wintering grounds and the Arctic.

Refuge manager Maria Fossado underscores how central this place is for migration.

“Wildlife are very smart, and they like to capitalize on use of energy,” she said. “Their focus is feeding, resting and capitalizing on when food is available.”

As the Arctic warms, some birds, like the Pacific black brant, are cutting their migrations short and spending the winter at the refuge. Williams says declining sea ice has made it easier to find the resources they need.

“It used to be, in the ’80s, a couple thousand. Increasingly, more of them are staying all winter long. Fifty to sixty thousand — the thought is, the lagoon is freezing over less, we’re getting less ice, and so the brant can access the eelgrass,” she said.

The lagoon is Izembek’s crown jewel. It hosts one of the largest eelgrass beds in the world. So why fly 2,800 miles to winter in Mexico when it’s plenty warm here?

“It might freeze up and then melt a couple times during the winter now, which is part of why people think that the brant are staying over more during the winter,” Williams said.

But overwintering has its costs. Brant don’t have to fly as far — but surviving an Alaska winter takes more energy than it does in a warmer place. Williams calls it a game of trade-offs.

A study published in March the journal Movement Ecology looked at brant over a 10-year period. It found the benefits mostly cancel out: the energy saved on the commute is about the same as the energy spent making it through the colder winters.

A fragile habitat holds on — for now

Beneath Williams’ kayak, there was a sprawling underwater meadow — the eelgrass beds that fuel the entire ecosystem.

“There’s a lot of things that live in the eelgrass,” Williams added. “It’s good habitat for a huge array of things.”

Tiny snails and clams burrow into it. Fish shelter inside it. And birds like the black brant depend on it for the energy to migrate — or overwinter.

The U.S. Geological Survey surveyed the eelgrass cover at Izembek in 2016 and 2020.

“There was some loss of eelgrass in the central part of the lagoon, where we are now,” Williams said. “And then a couple areas where we actually gained a little bit.”

Overall, the survey found a slight decline — far less than the global average. Worldwide, scientists estimate that about 30% of eelgrass habitat has vanished, hit hard by warming waters, pollution and invasive species.

Izembek remains one of the largest intact strongholds for this vital ecosystem. But in a warming world, even the most remote places are changing.