Effects of light intensity and of exposure to desiccation on the vertical distribution and growth of populations of marine benthic diatoms were investigated in a laboratory model ecosystem and a respirometer chamber. The diatom flora that developed in the ecosystem was similar to that from field stations in lower Yaquina Bay, Oregon. The vertical distribution of many species was closely related to light intensity and period of exposure to desiccation. Biomass accumulated most rapidly on substrates subjected to high light intensities, without exposure to desiccation. Communities acclimated to different light intensities and periods of desiccation responded differently to changes in light intensity in the respirometer chamber. Results of these experiments show that the laboratory apparatus described can be useful in the study of simplified intertidal communities.