Abstract <p>This study considers changes in the taxonomic, biogeographic, and trophic composition of polychaete worms in Kola Bay (Barents Sea) during periods of climatic variations and anthropogenic stress. Based on data collected within the periods 1934–1935 and 2021–2025, we have assessed the dynamics of quantitative characteristics of polychaete populations at 10 monitoring stations. Values of the key metrics such as taxonomic richness, abundance, biomass, and productivity have increased in the recent period. These trends are likely influenced by a combination of factors including warming, human activities, and differences in sampling methods between the 1930s and the recent benthic surveys. The findings suggest a high degree of adaptability among polychaetes in response to changing environmental conditions, as well as ongoing borealization trends within the bay’s marine ecosystem.</p>