Marine environment is a complex corrosive system and biofouling growth on immersed surfaces is one of the factors that influence corrosion processes. The effects of biofouling colonization on stainless steels (N08904 and UNS S32760) corrosion were investigated during 285 days. Open circuit potential (OCP) was measured in the absence (coupons isolated with meshes) and in the presence of biofouling. The dominant biofoulers were diatoms (during the first 15 days) and barnacles, filamentous macroalgae and encrusting bryozoans (from the 22nd until the end). Ennoblement in OCP values was different in the absence and in the presence of biofouling. In the absence of biofouling, OCP values remained stable at high values, while in the presence, after two to three months, OCP values decreased indicating localized corrosion development. Results indicated a significant correlation between the increase of the percent cover of encrusting bryozoans and the decrease of OCP. So far, the influence of encrusting bryozoans on corrosion process is unknown. Localized attacks that were registered were probably caused by live barnacles. Crevices were associated with barnacles' carapace and with calcareous base marginal addition. Nevertheless, a clear relation between OCP variation and crevice establishment was not detected.