Glacier retreat shapes organic nutrient availability across lake succession

Glacier retreat is rapidly transforming landscapes, creating thousands of new lakes that act as natural laboratories of ecological succession. In these newly formed ecosystems, colonizing animals must meet their requirements for essential organic nutrients, such as long-chain polyunsaturated fatty acids (LC-PUFAs). Here, we combined compound-specific stable isotope analyses of amino acids with fatty acid analysis to trace the origins and transfer of organic nutrients to fish (Arctic char) across a glacial-to-lacustrine lake succession in southern Greenland. Through lake succession, primary sources of nutrients shifted, coinciding with a 60% increase in LC-PUFA concentration in individual fish. In early glacial stages, Arctic char appeared to compensate for low LC-PUFA availability through endogenous biosynthesis of docosahexaenoic acid and, when connected to the fjord, by assimilating marine-derived nutrients via egg cannibalism. Overall, our results demonstrate that glacier retreat reshapes not only physical landscapes but also organic nutrient availability, with cascading consequences for animal physiology, ecosystem connectivity, and potentially long-term evolutionary trajectories.