Diversity and abundance of prokaryotes in Antarctica: the effect of oceanography in the Bransfield Strait

X Simposio de Estudios Polares, 15-17 May 2024, Salamanca

Microorganisms fulfill essential roles in marine ecosystems and their study is essential to understand their functioning. Despite its importance, in Antarctic waters, and particularly in the Bransfield Strait, there is little information about it. This study describes the spatial patterns of abundance and diversity of free-living and particle-associated prokaryotic communities (Archaea and Bacteria) in the Bransfield Strait. Oceanographic conditions were recorded at 13 stations, and in 7 of them the prokaryote community was analyzed at depths between 5 and 1000m. Each sample was separated into 3 size fractions, being able to differentiate free-living prokaryotes (0.2-3μm) from those associated with particles (3-20μm; 20-200μm). Prokaryotic diversity was analyzed by 16S rRNA gene sequencing (75 samples), and abundance was analyzed by flow cytometry. Diversity and abundance varied with depth: a greater abundance of prokaryotes was found in surface waters, and a greater diversity in deep waters. Similar diversity was observed in the three fractions when high-level taxa were considered (Phylum, Class), but significant differences were observed when considering low-level taxa (Genera and Species). The variables that most explain the composition of the community are depth (~20%), followed by lifestyle (~16%). The largest number of indicator species was found in deep water, followed by the free-living fraction. The composition of the surface water community is positively related to higher temperature and oxygen concentration, while deep communities were related to higher salinity. Specific prokaryotic communities were observed based on depth, ecoregion, water mass, and distance from Deception Island. These results show that there are prokaryotic communities that are structured according to the variables considered, and that the deep waters of the Bransfield Strait represent a reservoir of microbial diversity in this Antarctic area

Peer reviewed