Coastal bacterial community response to glacier freshening in Western Antarctic Peninsula

The current warming scenario in the Western Antarctic Peninsula (WAP) has multiple effects on the marine ecosystem, modifying the trophic chain and the nutrient regime. In Chile Bay (Greenwich Island, WAP), the effect of the decrease in surface salinity on the marine microbial community as a consequence of freshening from nearby glaciers, was analyzed by 16S rRNA-Tag sequencing and metatranscriptomics, together with isotopic rates of carbon and nitrogen. Marine transects along the bay, glacier-ice sampling, and manipulated salinity microcosm experiments were conducted during the austral summer of 2016. The results reveal that certain common seawater genera such as Polaribacter, Pseudoalteromonas, and HTCC2207 respond positively to downward changes in salinity in both, bay transect and manipulated experiments. These bacteria slightly decrease their relative abundance, but they still have the ability to develop their functional activities over time. However, other bacteria common on ice, such as Flavobacterium and Polaromonas eventually disappear from the marine system in response to the increased salinity in this system compared to ice. We suggest that all these bacterial members would be defined as potential sentinels of freshening events in the Antarctic coastal system. Furthermore, within photosynthetic eukaryotes there are also members that respond positively to the decrease in salinity, not affecting carbon fixation rates and guaranteeing optimal primary production in the bay. These results suggest that a significant part of the microbial community in Chile Bay, and possible in other coastal areas of Antarctica, are resilient and adapted to disturbances such as freshening due to the warming effect of climate change in Antarctica.