Bering Sea Blues
As global warming transforms the region, scientists are scrambling to study its diversity of species that depend on ice for survival
- Lisa W. Drew
- Feb 01, 2008
QUICK: WHAT DO YOU KNOW about the Bering Sea, that patch of blue on the map to the west of Alaska?
Your answer could be that an astounding half of the U.S. seafood catch comes from the region--including 2.5 billion pounds of walleye pollock turned every year into imitation crabmeat, fish sticks and fast-food fish filets. Or maybe you know that Yup'ik, Inupiat and Aleut people have lived off the Bering Sea's bounty for thousands of years. Or that ever since Russians happened upon the region's Pribilof Islands in the 1700s, human beings have been altering its rich ecosystem.
But even if you're a researcher who studies the area--even if you've read every scientific paper on the subject--you don't know exactly how some of its seabirds make use of areas of water amid the winter pack ice, or where its distinctive ribbon seals go in the spring after the ice melts, or why migrating gray whales were unusually skinny this spring after they left their Bering Sea feeding grounds.
No one does.
As one of the most remote and forbidding marine habitats on the planet, the Bering Sea still holds plenty of secrets--and it could hold onto them forever. Scientists worry that as the sea's ice shrinks with global warming, they may lose the chance to study its current web of life, much less understand future changes. "You just can't know what's going on if you don't know what you started with," says marine ecologist Alan Springer of the University of Alaska Fairbanks.
To figure that out, scientists from a range of government agencies and universities are collaborating to study the entire Bering Sea ecosystem. "We're looking at the whole composite," says marine biologist Jackie Grebmeier of the University of Tennessee in Knoxville. "From the physics that drive the physical system, to the atmosphere, to the zooplankton and phytoplankton that drive the biological system."
In particular, there's a special urgency to learn about sea ice and the creatures that depend on it. Though the extent of the ice fluctuates yearly, overall it does not extend as far in the winter as it once did, and in spring and summer, it is retreating earlier and faster. With it are going wildlife nurseries, molting sites, dens, hiding places, feeding grounds, resting spots, algae farms, hunting grounds and even transportation. "Certainly the lack of sea ice just as a platform is the most immediate, apparent and possibly deleterious consequence of warming in the Bering Sea," says Springer.
Of course, the Bering Sea is not the only place losing sea ice. So are the waters that surround Antarctica and that extend throughout the Arctic. Last summer, the Arctic ice melted to a record low, and some researchers were predicting that by summer 2050, the region would be virtually ice free. Others say the melting will happen even faster and more dramatically than that.
Along U.S. shores, dwindling ice directly affects the Bering, Chukchi and Beaufort Seas. The Bering Sea has drawn particular attention because of its world-class fisheries and the diversity of its 25 species of marine mammals; 38 species of seabirds; and hundreds of species of fish, crustaceans and mollusks.
Although the melting is giving urgency to the research, it's not as if researchers are looking at an untouched environment. "The Bering Sea has been subjected to a huge amount of abuse over the last three centuries, in one form or another," says Springer.
The exploitation began in the Pribilof Islands, which are critical breeding and staging areas 300 miles from the mainland. First Russians "ravaged the place," says Springer, almost eliminating the islands' fur seals and killing off entirely the local walrus and sea otter populations. In the mid-1800s, U.S. whalers took a huge toll on bowhead and right whales, and in the mid-1900s, several countries did large-scale, uncontrolled commercial fishing as well as additional whaling. In the Aleutian Islands, both the Steller's sea cow and Steller's spectacled cormorant were hunted to extinction.
Though the region's fisheries are now intensively managed, and the hunting of birds and marine mammals is regulated, many species have decreased in number over the past quarter century. They include the spectacled eider and Alaska's breeding populations of Steller's eiders, both federally listed as threatened. Populations of Steller's sea lions--now listed as endangered in the western part of their range--harbor and fur seals, sea otters, ocean perch and several species of crab have declined, some dramatically. The reasons, elusive and controversial, could include the impacts of commercial fishing in addition to the long-term effects of whaling and natural shifts in ocean temperatures.
At the bottom of the Bering Sea food chain, as anywhere, are tiny plants and animals. The difference here is that the ice itself is home to life-forms that live under conditions that would kill anything else. Known as extremophiles, they cling to the underside of the ice and colonize its interior, a spongelike maze of channels and watery pockets, coping with extreme cold and changing levels of salt and light.
Every spring, the melting edges of warming ice release the extremophiles and their waste into the water. This infusion of life and organic matter nourishes spectacular blooms of phytoplankton. The stuff sinks in huge quantities to the sea floor, where it feeds untold numbers of crustaceans, clams, worms and more. Those creatures in turn are dinner for bigger predators, which in the Bering Sea fall into two categories: those that can survive in the colder temperatures of the northern part of the sea and those that cannot.
In the warmer waters--particularly on the southeastern part of the continental shelf that extends out from Alaska--bottom-feeding fish and crabs consume much of the life on the sea floor. But in colder waters to the north, sea ducks, gray whales, walruses, bearded seals and other animals have long feasted on the bounty without much competition. The entire world population of spectacled eiders, for example, incredibly spends the dark Arctic winter packed into open areas of the ice in the northern Bering Sea, where the birds dive for clams and other food.
Last year, Grebmeier and colleagues reported that as colder waters grow warmer, the fish and crabs are moving northward. There's also evidence of less food for bottom-dwelling clams and worms, which means the sea may be becoming less productive. This past spring Grebmeier was out again measuring conditions from an icebreaker, and although she hasn't fully analyzed her data, "it looks like we're still in that decline mode," she says. "And we're looking at the movement of more temperate species as the warmer water is moving northward."
These new arrivals mean new mouths to feed, and researchers are seeing signs that there may not be enough to go around. Take the case of gray whales, which gorge on the greater part of their annual food supply every summer in the northern Bering and Chukchi Seas. The animals plow through sediment, filtering tube worms and fatty crustaceans called amphipods through their hairlike baleen--in the process reshaping the sea floor and stirring up vital nutrients. After fattening up, the whales migrate to their less bountiful breeding and calving grounds thousands of miles to the south.
If fish and crabs are devouring the amphipods, that may explain why biologists have found far fewer of the crustaceans in the whales' usual feeding grounds in recent years. That, in turn, may explain reports this summer of emaciated gray whales migrating along the coasts of California and Mexico. Some animals were so skinny that the outlines of bones were visible.
Like gray whales, walruses stir up the seabed. Almost all of the Arctic's walruses--perhaps 200,000, but that's only a best scientific guess--spend their winters in the Bering Sea. In spring they travel by the thousands with the heavy floes of retreating ice, hitching rides on ice sturdy enough to support large groups of them. "They depend on the pack ice to move them north," says biologist G. Carleton Ray of the University of Virginia. The walruses leave the ice to root for clams, worms and other food in relatively shallow waters, using their sensitive whiskers to locate prey. They often return to the same floes. Ray has calculated that walruses plow a combined area "in the order of thousands of square kilometers per year."
Many female walruses and their young go with the ice through the Bering Strait into the Chukchi and Beaufort Seas. There, the shrinking ice may be taking some into deep water beyond the continental shelves, which may explain why in 2004 Grebmeier and others on a ship in the Arctic Ocean saw nine walrus pups alone in deep water. This was strange. Walruses forage in shallower waters, and walrus mothers are attentive to their young. Females only bear one pup every two or three years, and the pups nurse for at least six months and sometimes as long as three years.
But that summer, unusually warm water from the Bering Sea had flowed into the Arctic Ocean. Rapidly melting ice may have taken walruses farther out to sea than usual and then vanished from under them. It seemed as if the pups had been separated from their mothers, and it also seemed that if the boat came across nine pups, many more must be out there. "They were getting tired and had no place to go," Grebmeier said at the time. "When they saw us, they moved closer, barking at us, but we didn't have any capacity or ability to save them. It really tugged at your heart, but there was nothing we could do for them."
This past October, thousands of walruses amazed biologists by taking to the shores of Alaska's northwest coast. The summer's record-breaking melt had erased the ice over the shallow continental shelf, and the animals simply could not dive deeply enough from the remaining ice to reach prey. So they moved to land, which unlike ice, will not be ferrying them to new feeding grounds every day.
Beached walruses, lost pups and skinny whales are only hints of what may be going on as the ice retreats. Here's another: In 1979, Canadian researchers examined ringed seal lairs near Baffin Island after an unusually warm April week that brought rain to the area. Ringed seals, which inhabit almost the entire Arctic, including the Bering Sea, are the only seals to spend winter deep in landfast ice, where they maintain their own breathing holes by clawing the ice to keep it from freezing (and where the seals are a favorite food of polar bears). That year the scientists found lairs with slumped roofs, melted roofs or no roofs at all. They also found newborn pups exposed on the ice, where they were easy pickings for polar bears and arctic foxes.
"From what we observed, it was clear how devastating unseasonal rain and warm temperatures could be to ringed seals," says biologist Ian Stirling of the Canadian Wildlife Service, who for many years has studied how polar bears have been stressed by dwindling ice. Yet at the time, he adds, "I could not have imagined the huge negative changes we have now documented with climate warming--loss of sea ice and threats to the future of ice-dependent species like polar bears and ringed seals--in such a short period as a working lifetime."
Lisa W. Drew teaches at Ithaca College in upstate New York, a region that may actually get colder as global climate change affects ocean currents. She frequently writes about Alaska.
Living on the Edge
The Arctic's indigenous peoples arguably are more affected by climate change than anyone else on the planet. Not only do they have front-row seats for observing the Earth's fastest-warming region, the warming is wreaking havoc on their subsistence lifestyles.
Dwindling sea ice is one of the most profound changes. It particularly affects the Arctic's several groups of Inuit--or Eskimos, as they are called in Alaska. For years, Alaska's Eskimos have reported thin and broken ice that even experienced hunters have misjudged and fallen through. Then there are less obvious hazards: Inupiat whalers rely on thick ice to hold the weight of whales they catch, for example, and thinner ice breaks up as they try to haul up their catch.
That's when the ice is there at all. Hunters once could depend on returning sea ice to seasonally deliver game to them. Now the ice doesn't always come back. That same ice once protected coastlines from the region's violent storms. But these days coastal erosion is literally dropping village houses into the sea.
NWF Priority: Fighting Global Warming
Combating global warming is a top priority for NWF, which is, among other activities, supporting national legislation to reduce greenhouse gases, publishing reports on warming's impact on wildlife and collaborating with state affiliates on grassroots efforts. For more information, visit www.nwf.org/globalwarming.
Climate Change and Shrinking Fish
Today the Bering Sea is providing about half the fish caught in U.S. waters and nearly a third of all fish caught globally each year. But results of a new experiment suggest that global warming may reduce that share dramatically as soon as the end of this century.
The study, led by researchers from the University of Southern California (USC) and University of Delaware, looked specifically at how climate change could affect the composition of Bering Sea phytoplankton, microscopic plants that form the basis of many of its food webs. According to USC marine ecologist Dave Hutchins, the sea's current high productivity stems in part from the dominance of diatoms, a particularly large kind of phytoplankton. "Because they're large, diatoms are eaten by large zooplankton, which are then eaten by large fish," he says. But Hutchins and his colleagues found that warmer conditions favor smaller phytoplankton over diatoms--a shift that could ripple throughout the ecosystem: As diatoms become scarce, animals that eat diatoms also would become scarce. "The food chain seems to be changing in a way that is not supporting top predators, of which, of course, we're the biggest," says Hutchins, who calls the study's results "harrowing."--Laura Tangley