ABSTRACT: In the last 2 decades, concerns regarding the effects of global loss of diversity have prompted considerable research on the functional consequences of biodiversity. In this context, a new perception of biodiversity as a major regulator of the functioning of ecosystems has emerged. The concept of biodiversity has a wide meaning and includes not only the number of species, but also the number of traits, relative species and trait abundances, etc. Understanding how these different components of biodiversity influence the functioning of communities is required in order to improve our ability to project the future consequences of the current rate of diversity loss. We used a short term manipulative experiment to disentangle the effects of species numbers, species traits (identity) and species relative abundance (evenness) on the primary productivity rates of intertidal macroalgal assemblages. We also examined the ability of functional identity and diversity indices to predict the magnitude of primary productivity and overyielding. Results suggested that the intense identity effects, derived from species traits, drove the response of the experimental assemblages. The relevance of species traits was confirmed by the significant effects of the community-level functional identity descriptors on the functioning of the assemblages. Also, weak but consistently positive effects were detected for evenness. Finally, the interaction between species richness and evenness suggested that the negative effect of high dominance by single species (i.e. low evenness) was more intense on those assemblages with reduced species richness. Thus, understanding potential interactions between richness, evenness and functional identity among other biodiversity components is critical to identify present and project future consequences of anthropogenic disturbances.