The “blue” or “Mediterranean” mussel usually occurs in the low intertidal of exposed rocky coasts with relatively high wave energy.  Though in its native range, it’s also found growing in dense patches on the sandy-muddy bottoms of brackish lagoons ( Ceccherelli and Rossi 1984).  Mytilus galloprovincialis is native to the Mediterranean, Black, and Adriatic Seas, however it has spread, mostly via ballast water and ship hull fouling to many other regions worldwide.  Though it’s cultivated as food for humans in some parts of Asia, in most of it’s non-native range, it has become a nuisance species, displacing natives, and the IUCN/SSC* Invasive Species Specialist Group has nominated Mytilus galloprovincialis as among the 100 "World's Worst" invaders.

*International Union for Conservation of Nature, Species Survival Commission