Wrack-derived coastal subsidies support brown bear (Ursus arctos) foraging via invertebrate prey on the White Sea coast (Russia)

Marine-derived subsidies link coastal and terrestrial food webs, yet their use by large terrestrial mammals remains poorly documented. We investigated wrack-associated foraging by brown bears (Ursus arctos Linnaeus, 1758) along the White Sea coast of the Onega Peninsula (Russia) using records of foraging instances from standardized coastal surveys (2015–2025) and invertebrate sampling (2025) of decomposing wrack deposits. We analyzed seasonal and spatial patterns using generalized linear models. We recorded 66 wrack-foraging instances during standardized coastal surveys. Foraging occurred across seasons, with peak activity in early spring (mean 10.0 instances per survey) and lower levels in autumn (3.39). Wrack-foraging activity varied among coastal sectors and was concentrated in the semi-enclosed Eastern Solovetsky Salma Strait, where model-based counts were higher than in Onega Bay (incidence rate ratio [IRR] = 9.98, 95% CI 2.97–33.5). Decomposing wrack contained abundant detritivorous invertebrates dominated by dipteran larvae of the kelp fly Coelopa frigida (Fabricius, 1805) and enchytraeid oligochaetes. Bears excavated moist wrack deposits and consumed invertebrate-rich material rather than macroalgal tissue. These findings indicate that wrack-associated invertebrates represent a predictable marine-derived food resource and reveal an underrecognized pathway linking coastal detrital systems to large terrestrial consumers.