Abstract <p>As part of an experiment to study biota in marine technoecosystems, the species composition and quantitative abundance of diatom microperiphyton in the water intake tunnel of Vladivostok TPP-2 were studied for the first time. Modern methods of algal flora analysis, including scanning electron microscopy, were used to identify 49 species of microalgae from the class Bacillariophyceae. A relatively high abundance of microperiphyton was noted on the surface of the macrofouling of the water intake tunnel (maximum density 17.4 ± 2.5 × 10⁶ cell cm^–2, biomass 56.3 ± 9.8 mg cm^–1). The dominant position was occupied mainly by benthic diatoms adapted to mixotrophic metabolism. The quantitative abundance of diatom microperiphyton in different sections of the water intake tunnel varied quite significantly (by 3–6 times) and was determined by the local hydrodynamic conditions.</p>