Terrestrial Inputs Shape Coastal Bacterial and Archaeal Communities in a High Arctic Fjord (Isfjorden, Svalbard)

Abstract

The Arctic is experiencing dramatic changes including increases in precipitation, glacial melt, and permafrost thaw, resulting in increasing freshwater runoff to coastal waters. During the melt season, terrestrial runoff delivers carbon- and nutrient-rich freshwater to Arctic coastal waters, with unknown consequences for the microbial communities that play a key role in determining the cycling and fate of terrestrial matter at the land-ocean interface. To determine the impacts of runoff on coastal microbial (bacteria and archaea) communities, we investigated changes in pelagic microbial community structure between the early (June) and late (August) melt season in 2018 in the Isfjorden system (Svalbard). Amplicon sequences of the 16S rRNA gene were generated from water column, river and sediment samples collected in Isfjorden along fjord transects from shallow river estuaries and glacier fronts to the outer fjord. Community shifts were investigated in relation to environmental gradients, and compared to river and marine sediment microbial communities. We identified strong temporal and spatial reorganizations in the structure and composition of microbial communities during the summer months in relation to environmental conditions. Microbial diversity patterns highlighted a reorganization from rich communities in June toward more even and less rich communities in August. In June, waters enriched in dissolved organic carbon (DOC) provided a niche for copiotrophic taxa including Sulfitobacter and Octadecabacter. In August, lower DOC concentrations and Atlantic water inflow coincided with a shift toward more cosmopolitan taxa usually associated with summer stratified periods (e.g., SAR11 Clade Ia), and prevalent oligotrophic marine clades (OM60, SAR92). Higher riverine inputs of dissolved inorganic nutrients and suspended particulate matter also contributed to spatial reorganizations of communities in August. Sentinel taxa of this late summer fjord environment included taxa from the class Verrucomicrobiae (Roseibacillus, Luteolibacter), potentially indicative of a higher fraction of particle-attached bacteria. This study highlights the ecological relevance of terrestrial runoff for Arctic coastal microbial communities and how its impacts on biogeochemical conditions may make these communities susceptible to climate change.

Coastal Microbial Communities Disrupted During the 2018 Hurricane Season in Outer Banks, North Carolina

“…It is equally important to take the results themselves into context when determining potential degrees of influence from seasonality. For example, our results support the type of microbial response one would expect from large amounts of terrestrial organic material input into a marine system (i.e., decreased community evenness and diversity, and increased copiotrophic lifestyles and metabolic pathways; McGovern et al, 2020 ; Delpech et al, 2021 ; Figueroa et al, 2021 ). Previous studies have demonstrated correlation between seasonality variables (e.g., temperature) and cyclicity in microbial community compositions ( Ward et al, 2017 ).…”

When a Year Is Not Enough: Further Study of the Seasonality of Planktonic Protist Communities Structure in an Ice-Free High Arctic Fjord (Adventfjorden, West Spitsbergen)

“…However, it is certain that other abiotic factors are also important and can interact with or stand behind changes in salinity to influence protists communities (e.g., seawater turbidity; unfortunately, not included in the study). In other words, as Delpech et al [63] documented for the structure of summer bacterial and archaeal communities of Isfjorden, reorganisation of protists community composition and functioning coinciding with gradients in salinity and nutrients (especially in melting season) could illustrate the significance of seasonal changes in terrestrial inputs.…”

Mechanisms Generating Dichotomies in the Life Strategies of Heterotrophic Marine Prokaryotes

“…In coastal zones, important allochthonous sources add to this and include organic pollution sources such as pulp industry (e.g., the work of [37]) and natural OC content in freshwater discharges. As the OC content in land runoff is influenced by precipitation, permafrost thawing [81], and ice melting [82], OC supply to coastal regions is believed to increase with climate change.…”

“…The L-strategy, on the other hand, is "superior" in terms of a potentially lower trade-off between competitive and defensive traits but feasible only in habitats that so far are more restricted in time and space. The oligotrophic oceanic gyres are expanding [92], and terrestrial supply of OC is expected to increase with climate change [81]. Habitat size for S-and L-strategist is, therefore, a feature of the marine microbial ecosystem sensitive to climate change on both local and global scales.…”