Abstract: Effects of water temperature (4, 18, 25 and 37 °C) on deep-sea bacterial biofilms and subsequent effect on metamorphosis of larvae of the mussel Mytilus coruscus were studied. The confocal laser scanning microscopy technique was used to clarify the characteristics of biofilms including biofilm thickness and the distribution of extracellular polymeric substances. The biofilms formed by the deep-sea bacteria could promote the metamorphosis of larvae under four temperature conditions. Virgibacillus sp.1 showed the highest inductive activity (35%), with high α-extracellular polysaccharide secretion. The Virgibacillus sp.1 biofilm inducing activities on larval metamorphosis were correlated to seawater temperature and bacterial density. Temperature was significantly correlated with bacterial density, induction activity and biofilm thickness. The densities of bacteria in the biofilms of the two Pseudoalteromonas strains were significantly correlated with the induced activity. The present study shows that deep-sea bacteria exhibited good potential for temperature change to form the biofilms, and impacted larval metamorphosis.