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Some of the richest biodiversity that resides in a sprawling archipelago nearly midway between Norway’s northern coast and the North Pole is ripe for inspection, not with high-powered binoculars, however, but with the exacting imagery afforded by the lens of a magnifying glass. The Svalbard Islands are home to polar bears, whales and walruses. Yet equally consequential in the island ecosystem are more than 1,100 species of invertebrates, including beetles, wasps, flies, moths, springtails, mites, aphids and spiders, that eke out a living in Svalbard’s soil, streams, and even on its glaciers.
Many of them have evolved unique ways of handling the extremes of the Arctic's seasons, relying on tricks like self-desiccation or natural antifreezes as survival mechanisms for the 10-month polar winter. During summer’s brief window, invertebrates rev up to play integral roles in the high-latitude environment, turning over nutrients to enhance the fertility of arctic soils.
Their usefulness aside, an overriding mystery remains as to how these organisms arrived in this forbidding spot. Steve Coulson, an arctic ecologist of The University Center in Svalbard, has a hunch. Coulson has spent more than 20 years sifting through soil, overturning rocks and swiping the air with butterfly nets in his pursuit of Svalbard’s invertebrates. He reckons that some of these small creatures may have originally hitchhiked their way to Svalbard by hiding in the plumage of migratory birds. Researchers refer to this form of freeloading as phoresy. If correct, Coulson says, “colonization to remote areas may be a lot faster than we thought.”
This summer, Coulson and his colleagues set out a handful of clam traps, or small netting tents that spring atop curious birds lured in by bait. After experimenting with a couple different size traps (40 by 40 centimeters was “too obvious”), they managed to bag 11 snow buntings, a common Arctic migratory bird. The team examined the snow buntings’ plumage for any invertebrates they may be carrying and then let the birds go.
They found three nonparasitic soil invertebrates: one oribatid mite and two mesostigmatid mites. One of those latter species had never been recorded in Svalbard before. “This implies that the mite must have come from the mainland to Svalbard on the bird, and therefore must have been on the bird for some time,” Coulson says. Avian delivery services were known to the likes of Charles Darwin, who suggested that birds may spread insect or plant eggs stuck to their feet or that the ova could survive a trip down their digestive tract. But as far as Coulson knows, no one has ever shown that soil insects with no parasitic ties to birds can travel long distances on a bird’s plumage.
This finding has implications for understanding both past and future colonization events on Svalbard. Although researchers have lacked clear knowledge of invertebrate history on the islands, they agree that most, if not all, invertebrates likely did not survive the last glacial maximum, which blanketed Svalbard in a sheet of ice for around 7,000 years. Rather, invertebrates reinvaded Svalbard after the ice subsided, beginning around 10,000 years ago. Birds, Coulson thinks, may have played a pivotal role in this process.
As the climate in Svalbard and the rest of the planet warms, it will likely widen the breadth of organisms that could potentially live in the Far North. But to become established, mites and other minute creatures must reach the archipelago. Normally, a researcher assumes that a tiny, flightless soil invertebrate may take thousands of years to find its way to a place like Svalbard by means of serendipitous mixing of ocean currents, winds and haphazard events. If invertebrates hitch a ride on migrating birds, however, these species may be arriving all the time. “Now, they can’t persist because it’s too cold, but if they are migrating already, it might just take a switch to the right climate,” Coulson says.
Questions remain, such as how long the mites can persist on their unsuspecting hosts, how many species may be undertaking this dispersal method and how often this occurs. To pursue answers, Coulson and another colleague, Natalia Lebedeva, have established the Avian Vectors of Invertebrate Faunas research project, or AVIFauna, an international team composed of ecologists, taxonomists and molecular biologists. Now that they have collected a few invertebrates, they plan to compare DNA sequences of the Svalbard hitchhikers with potential invertebrate source populations found in the birds’ overwintering locations in Russia and Europe. Their findings, they think, will apply to invertebrate colonizers on other polar islands as well. “It could be that dispersal to remote islands,” Coulson says, “happens much, much faster than we think.”