Salinity drives the biogeography and functional profiles of the oyster-associated microbiome along the Chinese coastline.

Understanding the influence of environmental factors on the taxonomic and functional profiles of microbial communities is critical for assessing ecological health. In this study, we perform a large-scale field survey and microcosm experiment to investigate the effects of environmental heterogeneity on the microbial communities and functional profiles of oysters along the Chinese coastline. We found that salinity altered the spatial distribution of oyster-associated microorganisms and their functional profiles between the southern and northern regions. Specifically, the northern regions, with optimal salinity (18.3 part per thousand), exhibited a higher abundance of dominant functional microorganisms, more stable microbial networks, and enhanced carbon, nitrogen, and sulfur biogeochemical cycles than the southern regions. Moreover, metabolic mutualism among key taxa, such as Vibrio, Pseudomonas, and Shewanella, was identified as crucial for the coupled carbon, nitrogen, and sulfur cycles. These results suggest that salinity-driven microbial interactions and compositions play predominant roles in structuring the spatial heterogeneity of the functional profiles of oyster-associated microorganisms. Microcosm experiments further confirmed that moderate salinity, a crucial indicator of climate change, regulates and enriches the primary functional profiles of oyster-associated microorganisms. Overall, this study highlights how environmental conditions shape oyster-associated microbial and functional traits along the Chinese coastline, raising concerns about the impact of anthropogenic activities, such as climate change, on marine ecological functions.