Mytilus coruscus is an important economic shellfish and a typical marine macrofouling organism in China. The process of settlement and metamorphosis in its life history is a necessary condition for the survival of larvae. The effects of cellulose on the biofilms of Pseudoalteromonas marina biological characteristics and its effect on the larval settlement and metamorphosis of M. coruscus were explored. Biofilms were cultured by different concentrations of cellulose (0.02, 0.2, 2 and 20 mg/L) with P. marina (initial bacterial density: 5×10⁸ cells/mL). The inducing activity of biofilms formed under different conditions was tested. The results showed, when P. marina biofilm formed with the cellulose concentration of 2 mg/L, the percentage of larval settlement and metamorphosis was 25%, which was significantly lower than that of monospecific bacterial biofilm. As the cellulose concentration increased, the bacterial density of the biofilm formed by P. marina and cellulose was greatly reduced, and reached the minimum at a certain concentration (20 mg/L). The bacteria were more dispersed and biofilm thickness were significantly reduced. Compared with monospecific bacterial biofilm, the biomass of α-polysaccharides, β-polysaccharides and lipids of biofilms formed with addition of cellulose was reduced by 72.55%, 62.01% and 66.23%, respectively. While for proteins, no significant difference was observed in the presence or absence of cellulose. In the process of P. marina biofilm formation, cellulose indirectly regulated the larval settlement and metamorphosis by reducing the production of extracellular polysaccharides and lipids. The findings may provide a theoretical basis for exploring the molecular mechanism of P. marina cellulose on the formation of biofilms and the settlement and metamorphosis of M. coruscus, and also provide new ideas for the treatment of biofouling.