In a culture experiment with microalgae metacommunities, we tested the effects of a regional heatwave disturbance on species diversity (richness, Shannon diversity) and turnover. The metacommunities consisted of three local communities with different initial community compositions. In our full factorial design, half of the metacommunities were subject to dispersal (every other day) and exposed to an experimental heatwave. Communities were sampled after 5, 12, and 21 days.