This work aims to examine the influence of various ecological parameters on periphyton colonization of artificial substrata by using multivariate analysis methods. The artificial substrata studied were the horizontal sides of a model of an artificial reef. This had been immersed at a depth of 11 m on a muddy sandy bottom, near the Marine Biology Laboratory (Trieste), since May 1988. To record periphyton colonization by phytosociological monthly sampling, the surfaces examined were subdivided into 44 squares of 20 × 20 cm. Temperature and salinity data were recorded twice a month by means of a computerized core-drill; sea water transparency by means of a Secchi disc. The ecological relationships, highlighted by multivariate analysis, among processes of colonization and physical parameter showed that the difference between surface-bottom temperature (thermocline) together with reduction in transparency acted synergically and interfered with the development processes of the periphyton.