As opposed to the acorn barnacle, bay barnacles can also survive in brackish water. They didn't originally belong to the original Dutch fauna. They probably arrived in the North Sea attached to a ship arriving from the eastern shores of the United States. Or possibly attachted to a whale. This is often how a small animal travels a long distance without exerting any effort. When Australasian barnacles inhabit the same area where bay barnacles already live, then the bay barnacle is often the weaker of the two and is displaced.