Plastics serve as substrate for microorganism (e.g. bacteria, protozoans, fungi and microalgae) colonization in aquatic environments, forming the Plastisphere. The Plastisphere in meso and microplastics from water and sediment collected in a salt marsh in the Patos Lagoon estuary (Brazil) was studied. For plastics in water, 150mL of water was filtered (0.45µm), and particles were selected from the filter under a microscope. For the sediment surface, plastics were manually sampled using tweezers in four zones: high marsh, middle marsh, low marsh and mudflat. All particles were analysed under a scanning electron microscope for attached microorganisms and degradation marks. Plastics (1.25-10.5mm in size) were found as fragments, pellets, films and fibres. In water, only fibres were found, and biofouling occurred in patches (not covering the entire surface). Microorganisms were found on all particles, including filamentous cyanobacteria, single-celled round- and rod-shaped bacteria, pennate and centric diatoms, and filamentous fungi, and yeasts. Broken diatom frustules were found mainly at the higher zones salt marsh. At the high marsh, biofilms also followed a patchy pattern on plastic surfaces, while in the mudflat and low marsh they were covering most of it. This might be associated with water availability, as lower zones are mostly flooded while higher zones are drier, which can cause desiccation of the fouling community. Also, fibres seemed to be less covered by microorganisms than other formats, which can be related to their smaller surface area available for colonization. Several degradation marks could be observed in the plastics surface in the high marsh, which can be a result of the less contact with water i.e. higher sunlight exposure. The patchy colonization pattern in that area could also favour photodegradation as biofilms can act as a protection against sunlight. Implications of biofouling in plastics remain to be studied in this area.