Salinity-induced metabolic reorganization in a long-lived marine osmoconformer Arctica islandica : Insights from contrasting arctic environments

Environmental salinity strongly shapes the physiology of osmoconforming marine invertebrates, yet population-level metabolic responses remain poorly understood. The ocean quahog Arctica islandica exhibits extreme geographic variation in growth and maximum lifespan, ranging from several decades in brackish environments to more than four centuries in fully marine habitats. The physiological mechanisms underlying these differences are unknown, although there are indications that habitat salinity may influence metabolic processes underlying life-history traits, including lifespan. We compared A. islandica populations from the fully marine Barents Sea and the brackish White Sea, acclimating individuals to three salinity regimes (17, 25, 33) spanning natural and experimentally altered conditions. Survival, tissue energy status, and whole-body metabolomic profiles were assessed. Quahogs from the White Sea and Barents Sea showed pronounced population-specific metabolomic signatures and distinct responses to salinity acclimation. White Sea individuals showed higher levels of glycine, proline, tyrosine, and tryptophan, as well as elevated oxidative stress markers (methionine sulfoxide, cystine) and glutathione metabolism at habitat salinity, indicating greater exposure to reactive oxygen species likely due to higher metabolic activity. Salinity shifts triggered differential regulation of amino acids, osmolytes, and urea cycle intermediates, with White Sea quahogs showing more pronounced osmolyte adjustments and tricarboxylic acid cycle flexibility. Despite substantial metabolomic remodeling, gross tissue bioenergetics, including proteins, carbohydrates, lipids, and electron transport system activity, remained stable. These results reveal population-specific strategies for salinity tolerance highlighting the metabolic flexibility of White Sea quahogs relative to the more conservative metabolism of Barents Sea individuals.