Mytilid mussels: global habitat engineers in coastal sediments

Abstract

Dense beds of mussels of the family Mytilidae occur worldwide on soft-bottoms in cold and warm temper- ate coastal waters and have usually been considered spots of biodiversity. We examined intertidal mussel beds at four distant locations around the globe with the same sampling method, to Wnd out whether this hot spot desig- nation holds universally. We studied species assemblages within the matrices of byssally interconnected mussels engineered by Mytilus edulis in the North Sea, by mixed Perumytilus purpuratus and Mytilus chilensis at the south- ern Chilean coast, by Musculista senhousia in the Yellow Sea and by Xenostrobus inconstans at the coast of southern Australia. In all cases, species assemblages inside mussel beds were signiWcantly diVerent from those outside with many species being restricted to one habitat type. However, species richness and diversity were not generally higher in mussel beds than in ambient sediments without mussels. In the North Sea (M. edulis) and at the Chilean coast (P. pur- puratus, M. chilensis), mussel beds have markedly higher species numbers and diversities than surrounding sedi- ments, but this was not the case for mussel beds in Austra- lia (X. inconstans) and the Yellow Sea (M. senhousia) where numbers of associated species were only slightly higher and somewhat lower than in adjacent sediments, respectively. In conclusion, although soft bottom mytilid mussels generally enhance habitat heterogeneity and spe- cies diversity at the ecosystem level, mussel beds them- selves are not universal centres of biodiversity, but the eVects on associated species are site speciWc.