Ulva sp. and Gracilaria sp. were found colonizing shell surfaces of an acorn barnacle, Megabalanus tintinnabulum. However, this association was not noticed in the case of Balanus amphitrite, which was a co-inhabitant. Such a difference in intergeneric interactions with the algae was examined in laboratory experiments. For this, the influence that extracts of algae, extracts of algae-associated bacteria and natural leachants from M. tintinnabulum exerted on cyprid metamorphosis of B. amphitrite was examined. Extracts of algae and associated bacteria showed no effect on the metamorphosis of B. amphitrite. This may be attributed to absence of cue-specific sugars in the exopolysaccharides and culture supernatants of bacteria. On the other hand, natural leachants of M. tintinnabulum, which showed the presence of N-acetyl-d-glucosamine, a known algal spore attractant, also inhibited metamorphosis of B. amphitrite. Thus, hosting specific epibionts could have important roles in the segregation of barnacle population.