A central question for ecologists is to understand processes patterning species assemblages, considering the relative importance of environmental gradients, biotic interactions or species dispersal abilities. Although it has been suggested that micro-organisms are everywhere and that only environmental variables selects, numerous studies have since showed that diatoms species could also be dispersal limited. Here we propose a (not exhaustive) overview of the main processes patterning diatom metacommunities, with illustrations from results we recently obtained. In particular, we tried to highlight processes related to species dispersal abilities, from an intercontinental dataset (US, Finland, France including tropical islands). In a second time, as particular beta-diversity patterns arise from such mechanisms, we tried to discriminate turnover and nestedness components from the total community dissimilarity and their relationships with environmental conditions.