Dietary modulation of gut microbiota enhances shell biomineralization and carbon sequestration in the freshwater clam Unio douglasiae taiwanicus

Bivalves play a dual role in aquaculture and biogeochemical cycles, yet their contribution to carbon sequestration remains debated. Here, we tested four dietary regimes— Chlorella vulgaris , Isochrysis galbana , fermented kraut juice, and Arthrospira platensis —in the freshwater clam Unio douglasiae taiwanicus to assess effects on growth, survival, gut microbiota, and carbon sequestration. Across 30 days, no significant differences in shell carbon sequestration were detected among diets, although patterns in growth and survival varied: Chlorella and Isochrysis promoted faster growth, Arthrospira supported the highest survival (95 %), and kraut juice altered microbiota composition, enriching Flavobacteriales . Microalgal diets instead favored Corynebacteriales and Clostridiales . These findings indicate that while short-term dietary interventions did not markedly alter carbon sequestration, they shaped physiological traits and microbial communities, providing insights into the role of diet in sustainable aquaculture and ecosystem services. • This study is the first to investigate the endemic clam Unio douglasiae taiwanicus , evaluating the effects of four dietary sources on growth, survival, gut microbiota, and shell biomineralization. • Carbonate deposition differed among dietary groups, indicating that diet can modulate the carbon sequestration capacity of freshwater clams. • Algal diets promoted faster shell growth and relatively high survival, while each treatment generated distinct gut microbiota compositions. • Functional predictions (COG, KEGG, Tax4Fun2) revealed diet-specific microbial metabolic pathways. • Diet–microbiome–biomineralization interactions provide insights into aquaculture nutrition and ecosystem services, while acknowledging limitations in experimental scale and duration.