The pivotal role of peatlands as reservoirs of ciliate diversity in Tierra del Fuego, Southern Patagonia

This is the authors' abstract. We don't add key points for this paper.

Peatlands are wetlands of global significance due to their high carbon storage and their role in supporting biodiversity and driving biogeochemical cycles. They are currently at risk, because of climate change and anthropogenic pressures, which may result in biodiversity loss. Despite their importance, peatlands of the Southern Hemisphere, particularly in Tierra del Fuego, remain poorly studied, especially regarding microbial eukaryotes such as ciliates. These are of particular interest due to their sensitivity to environmental changes and their central role in microbial food webs. We examined the ciliate composition across Sphagnum magellanicum moss and water bodies (clear and vegetated ponds) in two subantarctic peatlands of Tierra del Fuego (Rancho Hambre and Andorra). A total of 62 taxa were recorded, and taxonomic richness was higher in Andorra (44) than in Rancho Hambre (36). Community structure varied markedly among habitats, with distinct assemblages between ponds and the Sphagnum matrix driven by abiotic factors (e.g., conductivity and nutrients) and resource quality (e.g. DOC optical properties such as the E2/E3 ratio). Large mixotrophic ciliates (e.g., Thylakidium pituitosum , Ophrydium cf. versatile , and Bursaria sp.) were associated with nutrient-poor waters, with the large colpodid Bursaria sp. as a potential indicator. In contrast, small bacterivorous/algivorous ciliates (e.g., Halteria grandinella and Cyclidium sp.) dominated moss habitats, highlighting differences in trophic strategies across sites. Only a few species occurred across multiple habitats, suggesting strong environmental filtering and limited dispersal. The high ciliate diversity and specialized communities constrained by environmental conditions, reflect healthy yet fragile ecosystems. Ciliate diversity declined with conductivity and marginally with temperature, but increased with lower DOM molecular weight, highlighting the role of DOM quality and environmental gradients in shaping communities. These findings highlight peatlands as key contributors to biodiversity in southern regions and underscore the potential of ciliates as indicators of environmental variation in these understudied habitats.