If any single species has become the poster child for climate change, it is surely the polar bear. We all know the story: polar bears are creatures of the sea ice, and as Arctic sea ice continues its rapid decline, the future of polar bears is uncertain, with one study projecting that two-thirds of the global population could be extirpated by the middle of the twenty-first century.
But polar bears are far from the only animals at risk from declining Arctic sea ice, as a paper published today in the journal Science underlines. In the paper, a team led by Eric Post of Penn State University notes that retreating sea ice will have a number of other, not always immediately obvious, consequences for other wildlife in the region.
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For example, walruses rest on near-shore ice floes from which they dive to the bottom, feasting on clams and other shellfish on the seafloor. As sea ice retreats from the shore, the water becomes less shallow, forcing walruses into a choice: either they stay on the ice and expend more energy diving ever deeper in search of food; or they gather along the shoreline, leading to greater density of animals at such haul-outs, and increasing the risk of young walruses being trampled.
In fact, the seafloor community on which walruses depend may itself be at risk. During spring, as ice melts, algae that live in the ice drift downward into the water column and toward the sea bed, where they provide nourishment for the benthic organisms on which walruses and other animals feed. However, as water warms, zooplankton in the ocean may mature rapidly enough that they consume the algae before they have had the chance to complete their journey to the seabed. That's bad news for bottom feeders like walruses and bearded seals, but potentially good news for fin and humpback whales, which will have less ice with which to contend, and more food to consume in the water column.
The changes will even affect terrestrial animals, Post and colleagues write. Land adjacent to areas of sea-ice loss will experience significant surface warming inland from the coastline, affecting soil conditions and plant growth; as a result, terrestrial animals such as caribou could find their land-dwelling food sources disrupted due to temperature changes affecting plant communities inland.
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"Arctic sea ice should be thought of as a biome or an ecosystem and the effects of melting and warming on microorganisms living under ice in this biome already have received much attention. However, those animals living near the ice likely are feeling the effects, as well," Post notes.
"By viewing sea ice as essential habitat and a substrate for important species interactions, rather than as a lifeless blank surface, its loss as a result of warming becomes a rather stunning prospect."
Photo of blue sky breaking through the cloud above Arctic Ocean sea ice by Patrick Kelley, United States Coast Guard