In natural seawater, microorganisms can fix, grow and develop on practically any surface, including stainless steels, which may cause industrial issues such as microbial induced corrosion, loss of heat transfer efficiency, or undesired colonization from macro-fouling. In particular, the presence of a biofilm on passive alloys such as stainless steels or nickel-based alloys can strongly enhance the cathodic reactions such as reduction of dissolved oxygen, and shift the open-circuit potential (OCP) to the noble direction.This results in an increase in OCP, also called cathodic depolarization or biofilm-induced ennoblement, and affects the risk of localized corrosion, since the critical pitting or crevice potential can be exceeded.