The consequences of changes in biodiversity, natural and anthropogenic, for the functioning of coastal ecosystems are not known. To address this problem, two phenomena with regard to the (changes of) benthic biodiversity, occurring along the Mediterranean, Atlantic and Baltic coast, will be unravelled. Firstly, of two dominant benthic species, the blue edible mussel Mytilus sp. and the clam Macoma balthica, the strong northeastward shift in distribution of several ecotypes along the European coast, and the consequences for the coastal benthic community structure, will be assessed. Secondly, the impact of low species numbers in the Baltic, in comparison to a higher diversity in the Mediterranean and Atlantic, on the production of coastal ecosystems will be studied. The resulting indicators of biodiversity and (their relation with) ecosystem functioning will be relevant to managers of environmental (coastal) quality control.