Contrasting ecological patterns across deglaciating Western Antarctic Peninsula fjords revealed by soft-sediment benthic assemblages

Antarctic fjords are natural laboratories for assessing how global change and glacier retreat reshape marine benthic ecosystems, yet comparative studies integrating multiple components of soft-sediment assemblages remain scarce. Here, we assess three glacier-influenced fjords of the Western Antarctic Peninsula: Marian Cove, Börgen Bay and Sheldon Cove. Soft-sediment macrofauna and epibenthic megafauna were sampled along fjord-mouth to glacier-terminus gradients and analysed with hydrographic structure, assemblage composition, diversity, density, biomass, functional groups and a model-derived zoobenthic carbon proxy. Hydrographic structure varied from a shallow surface meltwater lens in Marian Cove to subsurface plume signals in Börgen Bay and Sheldon Cove. Assemblage composition shifted with glacier distance and fjord identity. Diversity increased towards fjord mouths, while glacier-terminus assemblages were more restricted; density, biomass, richness and carbon-storage potential showed non-linear or fjord-specific responses. These findings reveal deglaciating Antarctic fjords as mosaics of benthic ecological assemblages that may vary with local hydrographic and sedimentary settings, and provide a valuable baseline for future studies assessing temporal change in a warming Antarctica.