Experimental cryoconite holes as mesocosms for studying community ecology

Abstract

Cryoconite holes are surface melt-holes in ice containing sediments and typically organisms. In Antarctica, they form an attractive system of isolated mesocosms in which to study microbial community dynamics in aquatic ecosystems. Although microbial assemblages within the cryoconite holes most closely resemble those from local streams, they develop their own distinctive composition. Here, we characterize the microbial taxa over time in cryoconite holes experimentally created from supraglacial sediments to demonstrate their utility as experimental mesocosms. We used high-throughput sequencing to characterize the assemblages of bacteria and microbial eukaryotes before melt-in, then after one and two months. Within one month of melt-in, the experimental holes, now lidded with ice, were visually indistinguishable from natural cryoconite holes, and within two months their thermal characteristics matched those of natural holes. The microbial composition of the experimental cryoconite holes declined in richness and changed significantly in the relative abundance of various taxa, consistent with possible turnover. In particular, a dominant cyanobacterium, Nostoc sp., further increased its dominance over the other dominant cyanobacterial phylotype, and an initially rarer Flavobacterium sp. became one of the dominant taxa. The eukaryotes continued to be dominated by algae and tardigrades, with the relative abundance of the dominant alga, Macrochloris sp., increasing notably relative to the microfauna. These changes within a single growing season in newly formed lidded cryoconite holes created from exposed supraglacial sediments are consistent with primary production and microbial turnover, and provide a promising foundation for future work using such mesocosms.