The accumulation of biological materials and bacteria on water purification membranes, termed biofouling, is associated with decreased membrane performance and increased cost of operation. One strategy to minimize biofouling is pretreatment of the influent water. In this regard, tools and indicators that can assess the influent water are required, enabling an optimum selection of pretreatment methods. One parameter directly linked to biofouling potential is the concentration of assimilable organic carbon (AOC) in the feed-water. High AOC levels are associated with increased growth potential of the microbial fouling community. This work focused on the development of a new method for rapid and accurate quantification of AOC concentration in seawater. The method is based on the quantification of the bioluminescence response of the marine bacterium Vibrio fischeri MJ-1. Compared to previous methods, this new V. fischeri method was rapid (within 1 h), sensitive (detection limit = 0.1 mu g-C glucose equivalents/L) and highly suitable for seawater samples. V. fischeri method was evaluated using real seawater samples. The results showed positive reproductive AOC values. The new V. fischeri AOC method developed has a highly promising potential to be practically adopted as a rapid indicator of AOC concentration and hence biofouling potential of influent marine water. (C) 2013 Elsevier B.V. All rights reserved.