Desiccation, but not shading, substantially shifts the microbial community composition of benthic microbial mats in meltwater ponds near Bratina Island, Antarctica

Abstract

The Bratina Island meltwater ponds (McMurdo Ice Shelf, Antarctica) host complex microbial communities in the form of benthic microbial mats. These ponds are long-lasting but can experience significant alterations in physicochemistry on an annual or decadal basis, with additional alterations expected due to climate change. Here, we explored the impact of two potential future climate scenarios on the 16S rRNA gene sequence-based microbial community composition of three meltwater pond mats: desiccation (due to decreased precipitation and/or increased evaporation) and shading (due to increased precipitation resulting in increased ice cover). In a multi-year manipulation experiment, we found that the mat bacterial community composition shifted substantially with desiccation in all ponds studied. Desiccation reduced overall diversity, with cyanobacteria mostly being lost and members of the Bacteroidota phylum increasing in abundance. Halotolerance was indicated as a potential trait allowing for survival upon desiccation. We found that the community composition of the mats was resilient to shading (in the form of 75% light reduction), with no significant changes in composition observed. Instead, we observed a strong coloration change in the mats in response to shading, which could be due to positive phototaxis of Oscillatoria trichomes in the shaded mats. These results help inform how the prokaryotic communities in these highly productive mats may respond to future climate scenarios.