Trophic interactions in microbial mats on Byers Peninsula, maritime Antarctica

Cyanobacteria-based microbial mats are common in Antarctic terrestrial freshwater ecosystems such as the extensive wetland seepages that cover Byers Peninsula on Livingston Island (South Shetland Islands), maritime Antarctica, where they play an important role in biomass generation and productivity. Although cyanobacteria, microfauna and fungal communities have been described for such microbial mats, to date, little is known about trophic interactions within the mats, which are likely important to overcome nutrient constraints in oligotrophic polar freshwater ecosystems. We therefore carried out a biomass assessment of the different taxonomic components and their trophic interactions using DNA analysis and stable isotope analysis, as well as physiological activities such as primary and secondary production and nitrogen uptake within the mat food web throughout an austral spring and summer season. Our results suggested, based on a Bayesian mixing model, that carbon flow from cyanobacteria to upper trophic levels was limited to tardigrades and rotifers, whereas fungal and bacterial activity were likely the main connectors between consumers and producers via a heterotrophic loop. This suggests that homeostatic state displayed in freshwater microbial mats from maritime Antarctica provides stability to the microbial mats under the fluctuating environmental conditions commonly found in permanently cold shallow terrestrial aquatic ecosystems in Antarctica.