Benthic bacteria and archaea in the North American Arctic reflect food supply regimes and impacts of coastal and riverine inputs

Abstract

Benthic bacteria and archaea can be considered biogeochemical engineers as they play a major role in organic matter (OM) degradation and nutrient cycling. As such, prokaryotic community structure, yielded from 16S rRNA amplicon sequencing, can reflect environmental conditions such as OM composition and quantity, nutrient availability, redox conditions, and natural/anthropogenic contaminants (e.g. petroleum hydrocarbons). To assess prokaryotic community structure, we sequenced marine sediments in the upper 10-cm layer on the northern Bering and southern Chukchi Sea shelves, a high-latitude region undergoing rapid environmental change. We then explored broader spatial patterns in community structure for surface sediments (upper 1 cm), incorporating samples from the Northeast Chukchi and Beaufort Seas in relation to environmental variables. Three assemblages were characterized at distinct depth horizons in the upper 10-cm sediment layer from the Northern Bering and Southern Chukchi benthos. One assemblage was exclusively found in sediments at greater than 1 cm sediment depth and contained a relatively higher proportion of anaerobic taxa (e.g. Anaerolineaceae, Desulfobulbaceae, and Desulfosarcinaceae). Overall, community distribution in the upper 10-cm reflected sediment grain size, OM quantity and composition, and possibly the influence of bioturbation. Two assemblages were characterized in surface sediments (upper 1 cm) across the broader Northern Bering and Chukchi Sea study area. A relatively high abundance of anaerobic taxa (e.g. SEEP-SRB4, Subgroup 23, and R76-B128) in one assemblage suggested comparatively suboxic sediments, and the other suggested allochthonous input of phytodetritus based on high abundance of diatom/particle associated microbes (e.g. Polaribacter, Dokdonia, and Ulvibacter), combined with high sediment Chl-a concentration. This latter assemblage may reflect depositional areas influenced by hydrographic patterns. Prokaryotic community structure across the North American Arctic highlights regional differences in environmental controls, with food-supply regimes influencing structure on the Bering-Chukchi inflow shelves, in contrast to the Beaufort interior shelves where nearshore heterogeneity (riverine input and terrigenous material) are major drivers of sediment prokaryote communities.