Winners and Losers of Atlantification: The Degree of Ocean Warming Affects the Structure of Arctic Microbial Communities

Abstract

Arctic microbial communities (i.e., protists and bacteria) are increasingly subjected to an intrusion of new species via Atlantification and an uncertain degree of ocean warming. As species differ in adaptive traits, these oceanic conditions may lead to compositional changes with functional implications for the ecosystem. In June 2021, we incubated water from the western Fram Strait at three temperatures (2 °C, 6 °C, and 9 °C), mimicking the current and potential future properties of the Arctic Ocean. Our results show that increasing the temperature to 6 °C only minorly affects the community, while an increase to 9 °C significantly lowers the diversity and shifts the composition. A higher relative abundance of large hetero- and mixotrophic protists was observed at 2 °C and 6 °C compared to a higher abundance of intermediate-sized temperate diatoms at 9 °C. The compositional differences at 9 °C led to a higher chlorophyll a:POC ratio, but the C:N ratio remained similar. Our results contradict the common assumption that smaller organisms and heterotrophs are favored under warming and strongly indicate a thermal limit between 6 °C and 9 °C for many Arctic species. Consequently, the magnitude of temperature increase is a crucial factor for microbial community reorganization and the ensuing ecological consequences in the future Arctic Ocean.

Sea Ice as a Factor of Primary Production in the European Arctic: Phytoplankton Size Classes and Carbon Fluxes

“…This species develops when cells encounter high nutrient concentrations and increased light. The dominant phytoplankton groups were found to be more affected by meltwater input than by temperature in this area [59].…”

Transition from a mixotrophic/heterotrophic protist community during the dark winter to a photoautotrophic spring community in surface waters of Disko Bay, Greenland

“…Compared to some other Arctic phytoplankton species, Phaeocystis spp. have a wider tolerance toward temperature, as they are also commonly found in the Atlantic ( Hoppe et al, 2018 ), but may only be able to compete against temperate species to a limited degree ( Ahme et al, 2023 ). This increased fitness makes them a possible candidate for gaining importance in the Arctic spring bloom event in the future.…”

Biogeographic Analysis Suggests Two Types of Planktonic Prokaryote Communities in the Barents Sea

“…However, in recent years, there has been an increasing number of studies using metagenomics-based methods in the Arctic Ocean, which have revealed common patterns of prokaryotic diversity in this region. Such studies have been conducted in various parts of the Arctic Ocean and Northern Atlantic, including the Barents Sea, the deep Arctic Ocean, including the Eurasian and Canadian Basins, the Chukchi Sea, the Fram Strait, the Greenland Sea and the North Sea [23,24,26,27,[54][55][56][57]. A comparison of the lists of dominant prokaryote groups shows that the most widespread dominants in these communities are representatives of the Polaribacter, SAR11 and SUP05 groups.…”

“…The current number of studies examining prokaryotic diversity in the Arctic Ocean water column utilizing metagenomic methods and 16S rRNA metabarcoding is insignificant in comparison to its extensive territory and diverse hydrological conditions [22][23][24][25][26][27][28][29][30]. Nevertheless, the results already obtained allowed to the identification of the major groups of prokaryotes in the Arctic Ocean.…”