<p>While diatoms are crucial primary producers in a wide range of Antarctic marine habitats, those of benthic environments probably remain the least studied. For the first time in Scotia Bay, the taxonomic composition, abundance, biomass, and morphological traits of epilithic, epipsammic, and planktonic diatoms of mesolittoral sites exposed to a different impact of wind conditions (exposed vs protected) were assessed. In addition, the carbon contribution of benthic diatoms to the water column in mesolittoral and outer bay waters was quantified. A total of 111 taxa were identified, thus expanding the number of known diatom species for the area. Benthic assemblages were dominated by small naviculoid diatoms and displayed distinct spatial patterns: higher surface/volume ratios and biomass at the wind-exposed site, and greater richness at protected locations. Diatoms represented 85% of the planktonic protist biomass (up to 321.3 µgC L⁻¹), but the contribution of resuspended benthic diatoms in the plankton was low in terms of abundance, extremely low in biomass, and higher in the mesolittoral water column than in outer waters (6.5 vs 0.3 µgC L⁻¹) due to the dominance of large-sized colonial species. A low contribution of benthic diatoms to the total plankton biomass suggests low resuspension, a unique feature in the context of Antarctic coastal waters. Biomass quantification of the assemblages provides novel data on the contribution of organic carbon to local coastal food webs and draws attention to the need for further studies on the carbon stock and functional traits of the benthic diatom communities of Scotia Bay.</p>