Seagrasses and other aquatic plants are foundation species that modify the abiotic and biotic environment. Despite increasing numbers of studies on plant functional traits and ecosystem functioning in the terrestrial realm, analogous studies in marine environments and particularly seagrasses and other vascular plants are very few or lacking altogether.To bridge this knowledge gap, a functional group approach including the identification of important functional traits is needed. The main aim of this project is to investigate the relationship between plant functional diversity and ecosystem functioning (primary and secondary production, nutrient cycling) in temperate plant assemblages along environmental gradients. An additional aim is to investigate how such relationships may change with time, thus including temporal scales in the proposed research. The provided research will contribute valuable and highly needed information of the role of vegetated bottoms for the coastal functioning in the Baltic Sea. This will also form a novel research subject where the generality of hypotheses derived from terrestrial studies can be tested.