In order to obtain the useful information on the role of different bacterial strains isolated from middle wettability surface on the plantigrade settlement of the mussel Mytilus coruscus, the interaction between bacterial biofilms and plantigrade settlement was studied.The marine bacteria were isolated from the biofilms developed on the middle wettability surface and identification by 16S rDNA gene sequences was conducted.The effects of monospecific bacterial biofilms on settlement of M.coruscus plantigrades were investigated in the laboratory.The phylogenetic tree derived from the elected 16S rDNA sequence was constructed and the genetic distance was calculated.Of 6 different isolates, all bacterial biofilm showed significant inducing activity on settlement of M.coruscus plantigrades.Among the 6 bacterial species, Cobetia sp.3 biofilm induced the highest percentage of plantigrade settlement and the settlement rate was 70%±3%;Other 5 species of bacteria including Nautella sp.2, Pseudoalteromonas sp.9, Pseudoalteromonas sp.10, Bacillus sp.5 and Pseudoalteromonas sp.11 showed moderate inducing activity, and the percentages of of plantigrade settlement ranged from 51% to 60%.Bacterial density was significantly correlated with the inducing activity for each test strain.The density of monospecific bacterial biofilms increased with the initial incubation density.The inducing activity of individual bacterial isolates was not correlated with their phylogenetic relationship.Thus, marine bacteria derived from biofilms developed on moderate wettability surface can promote the settlement of plantigrades of the mussel M.coruscus. This finding is important to understand the mechanism of settlement of M.coruscus plantigrades.