Influence of sea ice dynamics on population energetics of Western Hudson Bay polar bears

Sea-Ice Retreat From the Northeast Greenland Continental Shelf Triggers a Marine Trophic Cascade

Climate change is causing sea-ice to retreat from Arctic ecosystems. Loss of ice impacts the ecosystem in many ways, reducing habitat area for specialist species like polar bears, releasing freshwater and nutrients, and increasing light penetration into the water column. To explore the interaction of these effects, we implemented a Northeast Greenland continental shelf parameterisation of the end-to-end ecosystem model StrathE2E. We used model output from the NEMO-MEDUSA ocean-biogeochemistry model under Representative Concentration Pathway 8.5 as driving data, which suggests the northeast Greenland continental shelf will become seasonally ice-free by 2050. We simulated half a century of climate change by running the model system to a set of steady states for each decade from the 2010s to the 2050s. Our simulations show sea-ice retreat from the northeast Greenland continental shelf boosts the productivity of the marine food web. Total living mass increases by over 25%, with proportionally larger increases for higher trophic levels. The exception to this is a 66% reduction in maritime mammal mass. Additional network indices reveal that the ecosystem becomes more mature, with future diets more specialized and a lengthening of the food web. Our model provides long-term strategic insight for the management of the northeast Greenland continental shelf, allowing for the quantitative evaluation of conservation goals and the scale of prospective fisheries. Our results present a mixed picture for the future of the Arctic, with growing populations for fish and charismatic megafauna like cetaceans accompanied by the loss of endemic biodiversity such as polar bears.

Energetic constraints drive the decline of a sentinel polar bear population

Human-driven Arctic warming and resulting sea ice loss have been associated with declines in several polar bear populations. However, quantifying how individual responses to environmental change integrate and scale to influence population dynamics in polar bears has yet to be achieved. We developed an individual-based bioenergetic model and hindcast population dynamics across 42 years of observed sea ice conditions in Western Hudson Bay, a region undergoing rapid environmental change. The model successfully captured trends in individual morphometrics, reproduction, and population abundance observed over four decades of empirical monitoring data. Our study provides evidence for the interplay between individual energetics and environmental constraints in shaping population dynamics and for the fundamental role of a single limiting mechanism-energy-underpinning the decline of an apex Arctic predator.