Effects of biofilms on settlement of plantigrades of the mussel Mytilus coruscus

The effect of biofilms developed in the aquariums on settlement of plantigrades of the mussel Mytilus coruscus was examined in the laboratory.Various aspects of biofilm biology were investigated including age,dry weight,chlorophyll a(Chl.a)content,bacterial and diatom densities.Bacterial community in biofilms was analyzed by the DGGE fingerprint technique.The correlation between the inducing activity of the biofilms and dry weight,bacterial and diatom densities,Chl.a content was also investigated.With the increase of biofilm age,dry weight,bacterial and diatom densities increased significantly and the maximum values were,respectively,0.87 mg/cm2,1.5×107/cm2 and 1.0×106/cm2 after 28 d.Furthermore,above three parameters were correlated with biofilm age.Chl.a content reached the maximum of 2.22 μg/cm2 after 14 d and no correlation between Chl.a content and biofilm age was observed.Plantigrades of M.coruscus preferred to settle on the biofilmed surfaces rather than the surfaces unfilmed.Overall the settlement of plantigrades on biofilms that formed in the aquariums increased with biofilm age,and the maximum of 76% settlement was obtained after 28 d.The enhanced settlement correlated to dry weight,bacterial density and diatom density,and their corresponding correlation coefficients were 0.717,0.711 and 0.754.In contrast,there was no correlation between inducing activity of biofilms and Chl.a content.Moreover,Shannon diversity index of bacteria community in DGGE profiles increased up to 28 d following immersion.The shift in bacterial community composition over time may be responsible for the higher settlement of plantigrades of M.coruscus on the older biofilms,indicating that bacterial community play an important role in the settlement of plantigrades in this species.