Diatom Diversity and Its Environmental Drivers in Lakes of King George (62° S) and Horseshoe Islands (67° S) in the Maritime Antarctic

Diatoms are key primary producers and sensitive indicators in polar freshwater ecosystems, responding to environmental change. This study investigates diatom species richness and the influence of environmental variables in fourteen coastal lakes on King George and Horseshoe Islands in the Maritime Antarctic. Water and surface sediment samples collected in 2017, 2019, and 2020 were analyzed using light and scanning electron microscopy, revealing 83 taxa (species and genera combined) across all lakes except one. King George Island exhibited higher species richness, with frequent occurrences of Planothidium lanceolatum, Fragilaria cf. capucina and Nitzschia cf. homburgiensis. On Horseshoe Island, common taxa included Achnanthes, Achnanthidium, Fragilaria, Nitzschia, Navicula, and Gomphonema. Among the previously measured water chemistry variables, HCO3− (ρ = 0.78, p = 0.005) and K+ (ρ = 0.69, p = 0.019) showed the strongest positive correlations with diatom species richness. Major ions and nutrients, as well as dissolved oxygen, salinity, and pH, exhibited moderate relationships. In contrast, temperature and trace metals displayed weak or negligible correlations, suggesting indirect influences on diatom diversity. These findings demonstrate that diatom communities in the Maritime Antarctic lakes are diverse and are shaped by variations in water chemistry, underscoring the ecological sensitivity of these freshwater ecosystems.