On Arctic landmasses, valley glaciers––formally known as tidewater glaciers––run all the way to the ocean, where cloudy plumes from their discharge create the perfect foraging habitat for seabirds. Researchers found some birds are reliant upon the turbid, subglacial freshwater discharge, which breaks apart icebergs and forms a column of freshwater foraging ground at the glacier’s edge, while others prefer to forage near the broken sea ice where water is less turbid.
In 2019, Bungo Nishizawa and associates published a study in the ICES Journal of Marine Science that investigated the effects of subglacial meltwater on two assemblages of seabirds in northwestern Greenland. One group included foraging surface feeders like the black-legged kittiwake. The other was comprised of divers, like the little auk. The researchers found that while the surface feeders congregate in the area of the cloudy plume, divers prefer to search for food where the water is less cloudy, spatially dividing the bird groups near the edges of glaciers.
Françoise Amélineau, a researcher of seabird ecology at the Norwegian Polar Institute, published a study in Scientific Reports last year, presenting the results of a 12-year monitoring program in East Greenland, which analyzed biological parameters of the little auk, the most common seabird in the Atlantic Arctic. Amélineau says that little auks use vision to detect prey and because meltwater plumes are so cloudy, the birds tend to forage farther offshore in clearer water, where they dive more than 20 meters below the surface.
A 2013 study in Polar Biology noted that little auks inhabiting West Spitsbergen, Norway also preferred to forage in clear water, far from glacier fronts, where they could easily identify water masses containing large, energy-rich prey.
Little auks usually feed in cold waters at the edge of sea-ice, up to 150 km away from their colonies. “In our Greenland study, we looked at sea ice concentration because some of the prey consumed by little auks are sympagic (associated to the sea ice),” said Amélineau, and “the little auks performed shallower dives in the presence of sea-ice, probably to feed on ice-associated amphipods”––a small type of crustacean. However, these ice-covered feeding areas are disappearing as the climate warms, which could make foraging more difficult.
Not only does a warming Arctic affect the presence of sea ice, it also alters the distribution of the little auk’s prey. Little auks feed on large zooplankton, which remain at depth in clearer waters. As the Arctic warms, the smallest (and lower calorie) Atlantic species of zooplankton is extending northward, threatening the range of the two larger (and higher calorie) Arctic species that little auks prefer. The invasion of the small zooplankton has the potential to negatively affect the fitness and breeding success of the little auk, which is thought to have the highest metabolic rate of all seabirds due to its small size and large flying and diving range.
With sea ice disappearing, the fate of little auk survival may be at risk. However, little auks from a colony of Franz Josef Land, located in the Russian Arctic, are actually taking advantage of a glacial meltwater plume––an adaptation that could be crucial. “We show that in Franz Josef Land, little auks have changed their foraging behavior with sea-ice retreat and the increase of glacier meltwater volume. At this site, they foraged at the glacier meltwater front instead of at more distant feeding grounds near the sea-ice because it allowed them to make shorter foraging trips,” Amélineau told GlacierHub.
Amélineau explained that “at the glacier front, zooplankton is stunned by cold and osmotic shock at the boundary between glacier melt and seawater, which makes it easier for little auks to catch. It probably concentrates their prey closer to the colony, but according to Nishizawa’s study, if the turbidity of the water is too high, meltwater plumes become unfavorable foraging areas for little auks who use vision to detect prey.” Discharge mechanisms can differ between glaciers, and this may be why little auks are able to utilize the Franz Josef Land differently than in Greenland, Amélineau added.
Black-legged kittiwakes are the most common type of gull in the world. While they do consume large zooplankton and small crustaceans, they mainly prefer to eat small fish and other marine invertebrates. While they are the only type of gull that dives and swims underwater, they make very shallow dives compared to that of the little auk, and are unhindered by turbid water.
Turbid subglacial discharge, which is unloaded 10-100 meters beneath the surface of the water, upwells at glacial fronts to form plumes that bring zooplankton, as well as marine worms and jellies from depth to the water’s surface. “The foraging behaviour of kittiwakes observed in the tidewater glacier bays revealed them to be swarming over the subglacial discharge, with rapid simultaneous nose-diving and plunging into the surface water in pursuit of rising prey,” according to one study in Scientific Reports.
While the size of meltwater plumes at glacial fronts are increasing with climate warming in the Arctic, apparently benefitting surface feeders, it is also important to consider the stage of glacial retreat. Kittiwakes, as well as other surface feeders, benefit most from deep tidewater glacier bays because they have strong discharges that upwell prey to the surface over a wide area.
According to the IPCC, the Arctic is warming twice as fast as the rest of the world. “While other species may be able to shift their distribution to higher latitudes or altitudes,” Amélineau said, “Arctic species may not find suitable habitat anymore.”
This is both ecologically and culturally concerning.
While little auks are ecologically considered a keystone species in the Arctic, they are also culturally important to the Indigenous peoples that live there. “They are hunted in Greenland,” Amélineau told GlacierHub. The Inuit “prepare a food called kiviak, where the little auks are fermented for 3 months in a seal skin!” Approximately five hundred of these birds are stuffed, whole, into the skin, and left in a pile of stones to ferment over the winter. They are a popular treat on weddings and birthdays.
Biological responses to changing climatic conditions are difficult to predict, particularly in remote locations that are already heavily impacted like the Arctic, where the ecosystem is already impacted by ongoing sea-ice decline and warming. Amélineau says this makes long-term seabird monitoring efforts extremely important, especially as these birds can be seen as ‘sentinels’ of what will happen at lower latitudes.