Supplementary Tables: Supplementary Table S1: Count data Cercozoa. Table S2: Count data Green Algae. Table S3: Count data Ochrophytes. Table S4. Sampling sites. Table S5. Diatom primers and tags designed for this study*. Table S6. Green algae primers and tags designed for this study*. Table S7. Primers used in this study. Table S8. Cercozoa, green algae, and ochrophytes included in the internal standards of each run. Table S9. Cercozoa cultures established in this study. Table S10. Algae and ochrophyte cultures established in this study. Table S11. One-way ANOVA comparisons of alpha diversity indices — OTU richness, exponential Shannon, and inverse Simpson— across polar biocrusts samples (N = 116) from Svalbard, the Antarctic Peninsula, and Continental Antarctica. Results presented separately for Cercozoa, green algae, and ochrophytes. The table displays F-values with degrees of freedom (df) for the nominator and denominator, along with associated p-values derived from one-way ANOVA comparisons. Table S12. PERMANOVA results for taxonomic groups across environmental factors. Analysis of polar biocrusts samples (N = 116) from Svalbard, the Antarctic Peninsula, and Continental Antarctica. Table S13. Network topological features, including inter- and intra-domain co-occurrences for Cercozoa, green algae, and ochrophytes. N = 116. Table S14. Summary of the ANCOVA models for predator counts. Table S15. Summary of the ANCOVA models for algae counts. Table S16. Summary of co-occurrence and correlation interactions identified in Cercozoan-algae HMSC networks across models.