Microbial dynamics and metabolic activity during fish decay under aerobic and anaerobic conditions: insights into microbial fossilization

Introduction: Understanding how environmental conditions influence early decay processes remains a central challenge in taphonomy, particularly regarding the relative roles of aerobic and anaerobic regimes. Because microorganisms drive soft-tissue decomposition, this study examines how contrasting oxygen conditions affect microbial community structure, metabolic potential, and the minerals formed during fish decay. Methods: S were monitored using microprobe measurements, and water chemistry was characterized through major ion analyses. Microbial community composition was assessed using 16S rRNA gene sequencing, and from this, metabolic potential was predicted using PICRUSt2. SEM-EDS and XRD were used to identify the precipitate minerals. Results: Oxygen availability resulted in markedly distinct microbial assemblages and decay trajectories. Anaerobic conditions were associated with lower pH and elevated hydrogen sulfide concentrations, whereas aerobic conditions maintained higher pH. Predicted metabolic functions were broadly conserved between treatments. Aerobic decay was characterized by higher DIC, lower DOC, and enrichment of genes linked to complete organic matter oxidation, including β-oxidation pathways. In contrast, anaerobic decay exhibited higher DOC, lower DIC, and increased abundances of genes associated with fermentation and carbohydrate metabolism, consistent with incomplete degradation. Mineralogical analyses identified magnesium phosphates and sodium sulfates in both treatments. Discussion: Environmental oxygen availability strongly controls microbial metabolism and decay dynamics. Aerobic microbial communities promoted more extensive tissue decomposition, whereas anaerobic communities favored slower, fermentation-dominated decay. The early mineral phases identified in both treatments likely represent precursors to diagenetic minerals and provide new insights into mineralization pathways that may contribute to exceptional fossil preservation.