Intensive oyster farming alters the microbial-regulated blue carbon storage in sediment

Intensive oyster farming enhances the organic matter coupling from water to sediment through biodeposition, potentially contributing to carbon storage. Microbes play a key role in regulating biogeochemical cycling in the coastal sediment. However, their specific contributions to carbon storage under oyster farming remain poorly understood. This study investigates microbial necromass and associated biogeochemical processes in sediments from an intensive oyster farm in Sanggou Bay, China, and compares these indicators with adjacent seagrass beds and bare zones. Additionally, carbon use efficiency (CUE) was employed to indicate microbial-regulated carbon cycling and storage in sediment. The results demonstrate that oyster farming promotes organic carbon accumulation in surface sediments but reduces its stability. Microbial necromass was identified as a critical driver of sedimentary organic carbon in oyster farm sediments, supported by enhanced nitrogen and sulfur cycling pathways. Notably, contrasting relationships between CUE and organic carbon were observed between the seagrass bed and the oyster farm. Functional metagenomic analysis further revealed distinct microbial metabolic pathways across habitats, highlighting the role of biodeposition in shaping microbial functions. These findings enhance our understanding of microbial contributions to blue carbon storage in aquaculture systems and provide new insights into coastal carbon storage beyond vegetated ecosystems.