Species interrupted

Melting of the Arctic ice at a rate faster than the rest of the planet is known for years. But little is known on how the ecology is responding to the fast change to a warm climate. New research shows many iconic Arctic species that are dependent upon the stability and persistence of sea ice are faring rather badly. Loss of polar ice habitat is causing a rapid decline in the numbers of ivory gull, Pacific walrus, ringed seal, hooded seal, narwhal, and polar bear.  

Ecosystems disturbed

Polar bears and ringed seals, both of which give birth in lairs or caves under the snow, lose many newborn pups when the lairs collapse in unusually early spring rains. These species may be headed for extinction. Rapid climate change is disturbing the ecosystems at a rapid pace.

Analysing data from a worldwide research effort, Eric Post and his collaborators found that most of the species affected by global warming in the Arctic are the ones that depend on the ice there for food, protection, and reproduction. Their habitats are changing rapidly along with the climate in the Arctic.

Spring is coming earlier each year in the Arctic as a result of which flowering plants and different kinds of animals are also showing up earlier than they normally do.

“The Arctic as we know it may soon be a thing of the past,” says Eric Post, associate professor of biology at Penn State University who headed an international team of researchers. The team’s results have been published recently in the journal Science.
The research documents a wide range of responses by plants, birds, animals, insects, and humans to the warming trend.

The scientists found that increase in mean annual surface temperature in the Arctic over the last 150 years has had dramatic effects. For example, in the last 20 to 30 years, the seasonal minimal sea ice coverage has declined by a staggering 45,000 square km per year.  The extent of terrestrial snow cover has declined steadily with earlier melting and breaking up as well as an earlier start to the growing season. “Species on land and at sea are suffering adverse consequences of human behaviour at latitudes thousands of miles away. It seems no matter where you look, on the ground, in the air, or in the water: we’re seeing signs of rapid change,” he declares.

The research reveals species once confined to more southerly ranges are moving northward. Among the most visible invaders are red foxes, which are displacing Arctic foxes from territories once too cold for red foxes.

Some of the less showy invaders that the scientists found are moving northward include the winter moth. It defoliates mountain birch forests and species of Low Arctic trees and shrubs, which in turn affect the dynamics of trace-gas exchange.

The presence of more shrubs and trees promotes deeper snow accumulation, increasing soil temperatures during the winter, and more microbial activity in the soil which makes the habitats more suitable for shrubs. Increasing the shrub cover may lengthen the period during the plant growing season when the tundra acts as a carbon-dioxide sink.
 
Species countering change

Musk oxen and reindeer are countering this change. They browse on shrubs, limiting their carbon-soaking capacity and northward expansion to the High Arctic. Grazing, trampling, and defecation by these herbivores promote growth and spread of grasses, which further attract geese. The geese in turn influence the productivity of lakes, where they rest and graze.

The research indicates complex aquatic and marine food webs like the above are extremely vulnerable to alteration due to changes in temperature, precipitation, and nutrient load from the land.

The consequences of Arctic warming have been dramatic so far, especially since the warming amounts to only about one degree Celsius over the last 150 years.
It is difficult to predict what will happen with the anticipated six-degree warming over the next century.

“The results of our studies so far reveal widespread changes, but also a surprising heterogeneity in biological responses to warming,” comments Post.

The study demonstrates how the wild reindeer on the Norwegian archipelago of Svalbard have benefited from the melting of snow during winter and perhaps from the earlier seasonal loss of snow cover.

With less snow cover and a longer growing season, these non-migratory reindeer have taken advantage of the increased plant abundance, with the result that reindeer populations and their ability to reproduce are up, while mortality is down.

In contrast, migratory caribou in low Arctic Greenland and elsewhere are declining in numbers. The caribou have not been able to adjust their calving season to keep it synchronised with changes in plant growth. Thus the time when the females need the food most no longer matches the time of maximum food availability. So, fewer calves survive.

Hotter summers may result in more insects and parasites to prey on the caribou, which in turn may reduce the annual caribou harvest by indigenous peoples.
“Inuit hunters at my study site in Greenland have all but given up on hunting caribou there. What will be the next component to disappear from their traditional lifestyle,” wonders Post.

 But why do some parts of the ecosystem appear to be unaffected by rising temperatures? Despite heavy harvest and changing environmental conditions, sockeye salmon production in Bristol Bay, Alaska, has remained relatively stable or even increased over the last century. Though hundreds of salmon populations are scattered throughout a range of habitats, the system somehow has compensated for these serious demands.  “People have thought of the Arctic as a relatively simple ecosystem that is easily understood, but in fact it is very complex. Not all populations within a given species respond similarly to warming,” explains Post.

*Musk oxen and reindeer are countering change by browsing on shrubs, limiting their carbon-soaking capacity and expansion to the High Arctic.

* Migratory caribou in low Arctic Greenland are declining in numbers.

* Loss of polar ice habitat has resulted in a drop in numbers of Pacific walrus, ringed seal, hooded seal, narwhal and polar beal