Genetic Background and Metabolic Influence on Long-Term Lithium Bioaccumulation in Mytilus Mussels and Their Hybrids

Abstract Marine mussels are widely used as sentinel organisms in coastal biomonitoring, yet the biological mechanisms controlling the bioaccumulation of emerging metals remain poorly constrained. Climate change and anthropogenic disturbances are reshaping species distributions and contact zones, promoting mussel hybridization that may alter physiological traits and contaminant-handling capacities. Lithium (Li) remains largely overlooked despite its potential toxicity and rapidly increasing global demand. Here, we investigate the influence of critical factors on Li bioaccumulation by mussels combining genetic background and isotopic approaches. Progenies of two Mytilus species and their hybrids were transplanted to the same Atlantic coastal site for 12 months. Over this in situ exposure period, Li concentrations show comparable temporal trends across all progeny groups, with an initial uptake-dominated phase followed by biodilution. Lithium isotope ratios (δ7Li) display a coherent temporal trend across all groups (decrease at early exposure, increase during later growth), and the magnitude of the shift differs slightly among genetic backgrounds. Across samples, δ7Li is coupled to growth-related metrics (dry weight) and inversely related to Li concentrations, indicating a metabolic control on Li isotope compositions of these organisms. Li concentrations are also positively correlated with lithogenic-associated elements (e.g., aluminum), consistent with the influence of particle associated Li. A simplified biodynamic modeling including Li isotopes data further indicates a more efficient Li depuration after 5 months, combined with a relatively stronger contribution from dissolved Li. Overall, growth-related factors emerged as the primary biological drivers of Li concentration and isotope variability, with the relative contributions of dissolved and particulate exposure pathways varying in association with physiological growth. Hybridization may modulate Li bioaccumulation and δ7Li values, but its influence appears secondary and does not compromise the use of Mytilus mussels as bioindicators in established frameworks such as “Mussel Watch”.