<b>Data from: </b><b>Cross-domain divergence in biofilm diversity responses to environmental variability in a glacier-fed stream</b>

Turbidity was consistently associated with alpha diversity across both domains, whereas temperature and nutrient associations differed between bacteria and algae and between environmental time dimensions. Lagged community dissimilarity showed the strongest association with beta diversity across models, indicating pronounced temporal dependence in community composition. <i>Hydrurus</i> abundance improved selected alpha-diversity models and explained algal-subcommunity turnover only under sub-daily variability.

Together, these findings demonstrate that co-occurring bacterial and algal assemblages within the same biofilm can exhibit contrasting spatial, temporal, and environmental associations, and that microbial responses to environmental variability cannot be inferred from a single biological group. The distinct behavior of <i>Hydrurus</i>-dominated algal assemblages further suggests that this mat-forming alga may modify the physical structure and microenvironment of biofilms, thereby influencing bacterial and algal coexistence and community turnover, which needs further investigation.</p>