The musselMytilus galloprovincialishas been studiedin situas a fouling organism in the north‐eastern part of the Adriatic Sea, in waters ranging from relatively clean to those contaminated by pollutants of urban and industrial origin (oil pollution, fish processing plant). Observations were made with artificial substrata (glass, wood, metal, PVC, wooden fishing ships) exposed for 7, 14 and 30 days and from 2 to 14 months. The studies included parameters such as frequency of occurrence, abundance, grade of abundance, dominance, length of valve, cover and biomass; the qualitative degree of pollution was also determined for each site investigated. Mussels prefer the mediolittoral and upper infralittoral zones, slight urban‐industrial pollution of organic origin, cleaner environments (primarily rich in food), shorter time of substratum exposure (up to one month), inert substrata (transparent glass, unprotected wood) and parts of ships protected from stronger water movements. The most unfavourable conditions for mussels include high silting (totally limiting), oil pollution (almost to totally limiting), nutrient‐poor coasts, long time of exposure (substantial fouling competition), toxic coating (particularly for wood), and parts of ships more exposed to high water speed when in motion.