Biofilm developed on stainless steel was characterised using biological, chemical and biochemical parameters, as well as aldose molecular biomarkers. Biofilm biomass and carbohydrate concentration increased on stainless steel, whereas C:N and organic carbon:chlorophyll a ratios decreased over the period of immersion. Despite the abundance of microalgal biomass, carbohydrate concentration was lower than that observed for proteins. Carbohydrate composition varied during the period of immersion. Glucose, arabinose and xylose were relatively more abundant during the initial period (5 d) of immersion, whereas rhamnose, fucose, ribose and galactose were more abundant during the latter period (greater than 5 d) of immersion. The sugar distribution trends suggest that biofilm carbohydrates were mostly derived from degraded biogenic and/or terrestrial sources, especially during the initial period (is less than 5 d) of immersion. As the period of immersion increased, the contribution of biogenic sources to the biofilm carbohydrates increased. This conclusion was also supported by principal component analysis based on wt % aldose composition. Multi-parameter approaches such as the one used in the present study provide a better picture of the sources and nature of biofilm organic matter