It was shown for the first time that the red alga Palmaria palmata (Linnaeus) F. Weber et D. Mohr, 1805 not only retained its physiological activity under the conditions of moderate pollution of the seawater with diesel fuel, but also exhibited a pronounced ability for sorption and destruction of petroleum products. The content of diesel fuel components in seawater decreased simultaneously with their accumulation in the algae. Apparently, the entire thallus of P. palmata participated in the destruction of diesel fuel: this process began on the algal surface via the activity of epiphytic hydrocarbon-oxidizing bacteria that provide the conversion of petroleum products into a plant-accessible form available for macrophytes. Subsequently, the petroleum products were neutralized by algal cells. The resilience of P. palmata under the influence of diesel fuel was confirmed by the consistently high metabolic activity of P. palmata cells throughout the 21-day experiment. It is assumed that the ability of macroalgae to form symbiotic associations with hydrocarbon-oxidizing microorganisms is the main factor in their bioremediation.