Melting Arctic threatens polar bear health

Arctic

Climate warming is transforming the Arctic in ways that impact every form of life in this harsh region. Rapid sea ice melting, habitat changes, and limited food availability are just a few aspects of this transformation. Polar bears (Ursus maritimus), acting as apex predators and key indicators of Arctic ecosystem health, are particularly vulnerable to these changes. The latest research findings indicate that climate warming increases polar bears’ exposure to diseases, including viruses and parasites previously unseen in the Arctic. Additionally, they are increasingly suffering severe injuries on unstable ice, another alarming sign of climate change’s impact on life in the Arctic.

Ecosystem under climate change pressure

Global warming accelerates changes in the Arctic, which promotes pathogen spread. Polar regions’ ecosystems are no longer free from diseases – on the contrary, animals living there are increasingly exposed to infections that were previously rare. As the study reveals, polar bears from the Chukchi Sea serve as bioindicators of these changes. Research published in the PLoS ONE journal, based on data analysis from 1987–1994 and 2008–2017, reveals an increase in seroprevalence – the presence of antibodies indicating pathogen exposure – among the polar bears studied.

The increase in pathogens and parasites may be linked to the longer time polar bears spend on land due to the summer disappearance of sea ice, as well as climate-driven shifts in species and their expanding ranges.

Study findings: rise in pathogen infections

Analyses from 1987–1994 and 2008–2017 showed a significant increase in seroprevalence – the percentage of polar bears with antibodies after contact with six pathogens. The highest increase, reaching 541%, was recorded for the canine distemper virus (CDV), which previously posed little threat in this region. Toxoplasma gondii and Neospora caninum, parasites not previously present in this part of the Arctic, are now commonly detected. Antibodies for Francisella tularensis and Brucella abortus/suis are significantly more common than in previous decades, which may result from changes in the food chain.

The study also found that pathogen exposure varies by sex and age. Females, who use terrestrial dens, were more susceptible to infection with certain pathogens, including F. tularensis and Brucella abortus/suis, than males. Additionally, white blood cell counts were significantly elevated in bears with a positive serological response to some pathogens, suggesting an immune response to infections.

Wodne Sprawy Topniejaca Arktyka zagraza zdrowiu niedzwiedzi polarnych 2
photo: Alexey_Seafarer/depositphotos

New threats related to diet and migration

The increase in T. gondii and N. caninum seroprevalence may indicate dietary changes and greater consumption of prey exposed to land-based infection sources. Research on polar bear diets shows that individuals seropositive for T. gondii consume more bearded seals, while those seropositive for F. tularensis prefer other seal species. This suggests that polar bears, forced off sea ice, are exposed to pathogens linked to consuming prey with more land contact, including microbes and parasites found on land and in freshwater.

Risk of physical injuries

Studies conducted in the Arctic also revealed that an increasing number of polar bears sustain injuries from the instability and melting of ice. Common injuries include cuts and abrasions on their paws, occurring as bears attempt to cross breaking ice surfaces or climb on steep, crumbling floes. These injuries have been particularly noted in bears living in the Beaufort Sea and Chukchi Sea regions, where sea ice is melting at an exceptionally rapid rate.

In the Kane Basin population, located between Canada and Greenland, as many as 51% of individuals (31 out of 61) displayed signs of ice-related injuries, including bald patches, cuts, and scars. In another population in eastern Greenland, similar injuries were observed in 12% of bears (15 out of 124). In 2022, two cases were also observed there of large ice chunks sticking to bears’ paws, making it difficult for them to move and hunt.

What does the future hold for polar bears?

The ongoing climate change is dramatically affecting polar bears’ lives. Limited access to sea ice not only forces them to spend more time on land but also exposes them to infections and injuries that previously posed no threat in their habitats. If climate warming continues, these issues will become more common, affecting the health and survival of this keystone species and the entire Arctic ecosystem, of which they are an integral part.

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