Mussels of the family Mytilidae occur worldwide in temperate waters, where they form dense aggregations on the sediment surface of soft-bottom coastal systems. In the largest sedimentary environment of the world, the European Wadden Sea (south-eastern North Sea), beds of the blue mussel Mytilus edulis provide a suitable habitat for a species rich community and a preferred substratum for invasive species. This mussel-associated community is much more diverse than the species assemblages of the surrounding sand flats and thus a hot spot of biodiversity. Do mussel beds have a general function as ecosystem engineers when compared with other parts of the world? Beds of different species of mytilid mussels and their associated species communities were investigated in Germany, southern Chile, South Korea and South Australia. In all coastal systems, mussel beds provided an additional habitat and supported a specific species assemblage different from the bare sand flats. Thus, the role of mussel beds as ecosystem engineers by increasing habitat availability and heterogeneity can be generalised over many coastal systems.