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. 2024 Mar 2;7(1):256.
doi: 10.1038/s42003-024-05946-8.

Biogeographic gradients of picoplankton diversity indicate increasing dominance of prokaryotes in warmer Arctic fjords

Cora Hörstmann  1   2   3 , Tore Hattermann  4   5 , Pauline C Thomé  6 , Pier Luigi Buttigieg  7 , Isidora Morel  8 , Anya M Waite  9 , Uwe John  10   11
Affiliations

Biogeographic gradients of picoplankton diversity indicate increasing dominance of prokaryotes in warmer Arctic fjords

Cora Hörstmann et al. Commun Biol. .

Abstract

Climate change is opening the Arctic Ocean to increasing human impact and ecosystem changes. Arctic fjords, the region's most productive ecosystems, are sustained by a diverse microbial community at the base of the food web. Here we show that Arctic fjords become more prokaryotic in the picoplankton (0.2-3 µm) with increasing water temperatures. Across 21 fjords, we found that Arctic fjords had proportionally more trophically diverse (autotrophic, mixotrophic, and heterotrophic) picoeukaryotes, while subarctic and temperate fjords had relatively more diverse prokaryotic trophic groups. Modeled oceanographic connectivity between fjords suggested that transport alone would create a smooth gradient in beta diversity largely following the North Atlantic Current and East Greenland Current. Deviations from this suggested that picoeukaryotes had some strong regional patterns in beta diversity that reduced the effect of oceanographic connectivity, while prokaryotes were mainly stopped in their dispersal if strong temperature differences between sites were present. Fjords located in high Arctic regions also generally had very low prokaryotic alpha diversity. Ultimately, warming of Arctic fjords could induce a fundamental shift from more trophic diverse eukaryotic- to prokaryotic-dominated communities, with profound implications for Arctic ecosystem dynamics including their productivity patterns.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1. Oceanographic connectivity.
a Map of fjords. Sample sites, color-coded to different regions. b Dissolved inorganic nutrient concentrations of nitrate (NO3), phosphate (PO4), and silicate (Si) in µmol L−1 in Sweden/southern Norway (n = 17), northern Norway (n = 30), Iceland (n = 3), Svalbard (n = 27), eastern Greenland (n = 3), and western Greenland (n = 4). Sites are color-coded as in (a), dark green boxes indicate regions without marine-terminating glaciers, orange boxes indicate regions with marine-terminating glaciers. c Trajectories of modeled drifters mapping oceanographic connectivity of individual fjords after 1 month, 6 months, and one year (see Figs. S2–S7 for connectivity matrices). See Fig. S10 for full tracking (up to 5 years). Sites and drifters are color-coded according to geographic regions of release where darker colors indicate higher drifter concentrations.
Fig. 2
Fig. 2. Picoplankton beta diversity distribution.
a Redundancy analysis (RDA) of CLR-transformed eukaryotic ASV table (30% of the variance in the ASV table constrained, p = 0.001, permutations = 999, n = 90); b RDA of CLR-transformed prokaryotic ASV table (43% of the variance in the ASV table constrained, p = 0.001, permutations = 999, n = 93). Colors and shape corresponds with geographic regions; c Aitchison distance of picoeukaryotic community composition against temperature differences between sites. Each site pair is color coded according to the absolute temperatures of each site with the site with lower temperature in the left half-circle and the site with the higher temperature in the right half-circle. d Aitchison distance of prokaryotic community composition against temperature differences between sites.
Fig. 3
Fig. 3. Alpha diversity scores in bioclimatic subregions.
a Boxplot of ASV Richness within each bioclimatic subzones indicating median, upper and lower hinges, whiskers and outliers. b Boxplot of ASV Pielou Evenness within each bioclimatic subzones indicating median, upper and lower hinges, whiskers and outliers.
Fig. 4
Fig. 4. Picoplankton trophic functional groups.
a Relative contribution of trophic functional groups of picoeukaryotes and prokaryotes of Arctic, subarctic and temperate regions. Annotated taxa are summarized in Supplementary Data 2. CLR-transformed ASV tables of picoeukaryotes and prokaryotes were merged and normalized to 1. b sum of each trophic functional group within bioclimatic subzones showing medians, upper and lower hinges, whiskers and outliers. For each trophic functional groups, the boxplots are ordered from top to bottom: Arctic – subarctic – temperate.
Fig. 5
Fig. 5. Oceanographic connectivity between sites.
a Aitchison distance analysis of picoeukaryotic community composition (18 S rRNA sequences) against hydrodynamic distance defined as the inverse of the log10 of the synthetic drifter concentration normalized to the range from 0 to 1. Correlations are color-coded and Pearson correlations calculated for each temporal bin. Sites without oceanographic connection are not included; b Aitchison distance analysis of prokaryotic microbial communities (16 S rRNA sequences) against hydrodynamic distance defined as the inverse of the log10 of the synthetic drifter concentration normalized to the range from 0 to 1. Correlations are color-coded and Pearson correlations calculated for each temporal bin. Sites without oceanographic connection are not included.
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