It is not native. The blue mussel has a blue-black to dark brown shell, with a smoother, more rounded shape than its native relative. The inside of the shell is a pearly, blue-grey. They attach themselves to rocks, wharf piles, boat hulls and each other using strong, silky byssus threads. A mussel that glues itself to anything. These animals are the colonisers of the disturbed shore. They are more tolerant of pollution, sedimentation and wave action than the native green-lipped mussel, which allows them to thrive in harbours, estuaries and urban coastlines. They are also a major pest on boat hulls, where they create drag and increase fuel consumption. A mussel that goes where others cannot. A single blue mussel can filter up to five litres of water per hour, removing algae and organic particles. A bed of thousands can clean an entire harbour. They are the unsung heroes of water quality, working silently to keep coastlines clear. A mussel that cleans as it feeds. Blue mussels are the mussels of the European shore, transplanted to New Zealand. They are smaller than the green-lipped, with a milder, less sweet flavour. They are often sold as small mussels in supermarkets, used in paella, pasta and seafood chowder. To see a blue mussel is to see the introduced coloniser. A small, tough, blue-black bivalve that has made itself at home on every wharf, every rock and every boat in the country. They are a European transplant that has found a happy home in New Zealand waters. Arrived from Europe in 1800s, probably as larvae in ship ballast water or attached to hulls. Spread throughout New Zealand, now one of most common mussels on rocky shore. The wharf pile is black with mussels, blue-black shells clustered tight. The water flows through them, clean on one side, cleaner on the other. They do not know they are introduced. They do not know they are invasive. They just filter. That is what mussels do.