From barrier to gateway: Climate‐facilitated expansion of thaliaceans in the Arctic Ocean

Abstract Thaliaceans (doliolids, pyrosomes, salps) play fundamental roles in global carbon cycling and pelagic food webs through high filtration rates and rapid reproduction. Despite their prevalence, they are virtually absent from the Arctic Ocean. This paper explores the ecological, physiological, and historical factors that may have contributed to this apparent absence and discusses whether climate change could facilitate future colonization. The extreme Arctic Ocean environment, characterized by perennial and seasonal sea ice, low temperature, reduced salinity from freshwater inputs, and high particulate loads, creates formidable barriers to the establishment of thaliacean populations. These conditions likely constrain feeding efficiency, buoyancy regulation, and reproductive success, while the strong seasonality and limited primary production further reduce habitat suitability. Comparisons with the Southern Ocean reveal that low temperature alone is not the sole limiting factor. Several thaliacean species persist in Antarctic waters, suggesting that Arctic‐specific features such as low salinity and particulate‐rich surface layers may act as barriers to thaliacean colonization. Rapid Arctic Ocean warming, declining ice cover, and the borealization of pelagic ecosystems are transforming these constraints. Increasing open‐water duration, enhanced nutrient fluxes, and greater primary production may create ecological windows for thaliacean expansion. If thaliaceans establish viable populations, they could substantially alter Arctic food webs by competing with native grazers and accelerating vertical carbon export. While the conditions in the Arctic Ocean may long have functioned as an ecological barrier to thaliaceans, climate‐driven change could enable their northward incursion, with potentially far‐reaching implications for biogeochemical and trophic dynamics, and socioeconomic services alike.