The polar bear, Ursus maritimus, is a large marine mammal adapted to the Arctic environment. Its Latin name, meaning “maritime bear,” describes its dependency on the sea and the pack ice of the circumpolar Arctic. These carnivores inhabit the frozen regions surrounding the North Pole, including areas of Canada, Alaska, Russia, Greenland, and Norway. Unlike other bear species, the polar bear spends most of its life on the sea ice, using it as a platform for hunting and travel. This specialization makes the species a powerful ecological force in the Arctic.
Apex Predator Status
The polar bear occupies the highest position in the Arctic marine food web, functioning as a hypercarnivore and top-level predator. They exert top-down control on populations below them, a concept known as a trophic cascade. Their diet consists almost exclusively of seals, particularly fat-rich Ringed and Bearded seals, which provide the energy necessary to survive the frigid environment.
Predation pressure stabilizes the ecosystem by preventing the overpopulation of seals. If the bear population declined, seal numbers would likely increase unchecked. This surge in seal consumption of fish and invertebrates would destabilize the lower food web. The polar bear is a regulatory force, ensuring no single prey species dominates the Arctic ocean’s limited resources.
The selective hunting of seals on the sea ice is a highly specialized behavior. This constant pressure on seal populations helps maintain biodiversity and the structural integrity of the marine food web. The removal of this top predator would fundamentally alter the Arctic’s ecological balance.
Role in Nutrient Distribution
Beyond population control, polar bears transfer energy and nutrients from the marine environment to terrestrial and ice-based ecosystems. Their hunting style involves dragging prey onto the sea ice, ensuring a significant portion of the carcass remains. These abandoned seal remains, consisting of marine fats and nitrogen, become a food source for Arctic scavengers and decomposers. Researchers estimate that bears collectively leave behind approximately 7.6 million kilograms of prey annually. This substantial carrion acts as an energy bridge, fueling life where resources are scarce.
Species like Arctic foxes, gulls, ravens, and wolves rely on these leftovers to survive, especially during lean periods. The nutrients consumed by the bears are recycled into the terrestrial food chain through this scavenging activity. This material transfer supports smaller mammals and birds that lack direct access to the ocean’s food supply.
Indicator of Arctic Health
The polar bear functions as a sentinel species; its health and population status serve as a measurable metric for the overall stability of the Arctic ecosystem. Their existence is linked to the presence of sea ice, which they rely on for hunting, resting, and breeding. As the Arctic warms and sea ice melts earlier, the physical condition and reproductive success of polar bears directly reflect the severity of climate change impacts.
Because they are at the top of a long food chain, polar bears are highly susceptible to the bioaccumulation and biomagnification of environmental contaminants. Toxins such as Persistent Organic Pollutants (POPs) and heavy metals like mercury accumulate in the fat reserves of seals and are then concentrated at high levels in the bears. The concentration of these contaminants in their tissues provides scientists with a measure of pollution levels across the remote Arctic.
Differences in mercury bioaccumulation between populations have been linked to the varying structures of regional food webs. Monitoring the physical condition, reproductive rates, and contaminant burden of the polar bear provides integrated insights into the health of this rapidly changing global environment.