Unlike dunes, sandy beaches and the littoral zone are usually regarded as non-vulnerable. The biodiversity and biomass of interstitial organisms are low. How-ever, recent findings have shown that marine sands transfer energy very ef-fectively, and that chemical and biological reactions take place faster there than in fine-grained sediments. The importance of the microphytobenthos and bacteria to this system is little known. The effects of recreational pressure (trampling, beach cleaning and nourishment) are not well understood. A pilot study from the Baltic Sea shows the importance of trampling as a form of bioturbation, a very effective way of fragmenting and mixing organic matter with the sand. The high diversity of diatoms and meiofauna in undisturbed beaches may act as an effective biological filter for some types of pollutants, while less diverse, but more abundant biota in disturbed areas are more effective in processing organic matter (self-cleaning of the beach).