Figure captions
Figure 1. Map showing the location of the stations sampled during September 20–23, 2018. At each station triplicate sediment cores were collected and the top 0–2 cm sediment surface sliced. The study area is located in the Gulf of Finland (Baltic Sea) nearby the Tvärminne Zoological Station (TZS). The numbers denote each station name. Stations 11, 12, 15, 16 were grouped as “Low OC”, and stations 7, 10, 13 as “High OC” based on the % OC content. The map layer is © OpenStreetMap contributors.
Figure 2. The boxplots show the species richness Chao1 and Shannon’s H alpha diversity index for the three taxonomic groups studied in the sediment surface in the Low OC and High OC stations. The data are based on 18S rRNA sequences extracted from the RNA-seq data, with (a–c) showing Chao1 and (d–f) showing Shannon’s H. Note the different scale on the y-axes between the three taxonomic groups. The P values show the results from One-Way ANOVA tests between the Low OC and High OC (only shown if statistically significant). The outliers denote, circles: 1.5–3 box lengths from the median, and stars: 3 or more box lengths from the median.
Figure 3. NMDS plots showing the beta diversity of the three studied taxonomic groups in the sediment surface, featuring (a)Nematoda , (b), Foraminifera , and (c) Ciliophora . The beta diversity was based on the 18S rRNA data and the Sørensen index (presence/absence, labels show station numbers). The light blue shaded areas denote Low OC stations, while dark blue shaded areas denote High OC stations. The P values show the results from PERMANOVA tests between the Low OC and High OC stations.
Figure 4. CCAs showing the distribution of (a) Nematoda , (b) Foraminifera , and (c) Ciliophora among the Low OC stations (light blue circles) and High OC stations (dark blue circles). The data was based on the relative abundances o genera for each taxonomic group. The grey triplots shows the direction of to the measured abiotic variables (water depth, sediment % OC and % N, plus pore water NH4+ and PO43-) in relation to the community composition. Each circle represents one sediment core. The Pvalues shows the statistical significance (PERMANOVA) between the abiotic data and community composition when tested between Low OC and High OC stations.
Figure 5. The stacked bars show the taxonomic classifications for the groups (a) Nematoda , (b) Foraminifera , and (c)Ciliophora based on 18S rRNA data (nematodes and forams classified against NCBI NT, and ciliates against the SILVA database). The y-axis shows the station names, their water depth (m), and replicates denoted with A, B, C. The x-axes show the relative abundance (%) within each taxonomic group. Taxonomic classifications that are significantly different between Low OC and High OC sites mentioned in the results have been indicated with bold text.
Figure 6. Nematoda genera were classified into a feeding type category according to Wieser (1953) and the plot is based on the sum of all classifications between the Low OC and High OC stations. DESeq2 statistical analyzing showed significant differences for all feeding types (FDR < 0.05 = *, FDR < 0.01 = **). Negative log2 fold change values indicate a higher prevalence at the High OC stations (dark blue circles), while positive values indicate a higher prevalence at Low OC (light blue circles). The errors bars show the standard error.