The Xiamen Symposium on Marine Environmental Sciences (XMAS 2027)

Mobile genetic elements (MGEs) drive genomic plasticity in marine microorganisms and facilitate the transfer of antibiotic resistance genes (ARGs) among hosts. Yet the global biogeography of distinct MGE classes, their environmental regulators, and their differential coupling to the ocean resistome remain poorly resolved. Analyzing 1735 marine metagenomes across the global ocean, we quantified five MGE classes: plasmids , phages, conjugative elements, insertion sequences, and integron-associated gene elements, . Each class exhibited a unique global distribution. Phages dominated the mobilome numerically, followed by plasmids. However, total MGE abundance was a poor predictor of ARG abundance. Resolving this signal by class revealed opposing trends: plasmids, integrons, conjugative elements and insertion sequences all correlated positively with ARGs, whereas phages correlated negatively. At the genome level, plasmids carried the most ARG-adjacent loci and phages ranked second despite their numerical dominance.  We term this scale-dependent pattern the abundance-linkage decoupling: the most abundant mobile elements are not necessarily the dominant physical vectors of resistance. After accounting for environmental variation, plasmid abundance remained the strongest predictor of total ARG abundance. Our findings demonstrate that numerical dominance does not equate to functional dominance for MGE-borne cargo, and imply that ocean warming, nutrient shifts, and anthropogenic pressure will act on the marine resistance reservoir through element-specific pathways.