Metabolomics has shown considerable potential as a tool for environmental toxicology. Both GC-MS and NMR techniques have been widely used in metabolomics and metabolite profiling. GC-MS is particularly effective in the analysis of primary metabolites, while NMR, Compound Library inherently quantitative, provides universal detection for organic components without coupling to a separation technique. Because of the complementary analytical features of NMR and MS, opportunities for leveraging both methods are being considered which will create a more comprehensive metabolic profiling. It is now well known that synthesis of antioxidant and metalchelating components and activation of antioxidant enzymes are key factors for tolerance to heavy metals and other abiotic stress in plants. The toxic effect of heavy metals appears to be related to production of reactive oxygen species, which usually leads to lipid peroxidation and oxidation of some enzymes and a massive protein. To better understand oxidative stress under acute and chronic conditions, the content of malondialdehyde, which represents the level of lipid peroxidation, was measured, as well as the activities of antioxidant enzymes superoxide dismutase, catalase and peroxidase. Additionally, activity of nitrate reductase that primarily involved in maintenance of a favorable cellular oxidation/reduction potential was also determined. In this study, we characterized the impact of Cu on the marine brown algae S. fusiforme using both NMR- and GC-MS-based metabolomics, which allowed identifying more analytes and created an opportunity to expand the scope of metabolomics research. ROS were formed either after acute or chronic heavy metal exposure, where the former abruptly generated into high levels that exceeded the ability of the antioxidant system to cope with them, while the latter increased steadily, resulting in different levels of damage to cellular compounds. Mannitol is almost universally present in brown algae, being the main product of photosynthesis instead of sucrose, which may also function as carbohydrate storage, translocatable assimilate, source of reducing power, osmoregulator and/or antioxidant. Changes in the monnitol content of marine brown algae have been reported in many field-based studies except that of heavy metal. Based on the visual inspection, mannitol is the most abundant metabolite in the NMR spectrum from tissues of S. fusiforme. A mannitol cycle has been proposed in a number of organisms, including micro and macroalgae, where the latter is essentially the same as the fungal cycle. In some yeasts, Cu2+ supplementation activates mannitol dehydrogenase involved in the biosynthesis of mannitol, resulting in an increased mannitol production. However, little is known about the affection of Cu on these enzymes involved in the metabolism of mannitol, especially in brown algae. At the cell membrane, Cu may interfere with cell permeability. In the present study exces Cu treatment caused much mannitol lost in the cell of S. fusiforme, indicating an enormous increase in permeability to it.