Deliberate lateral and vertical movements by mussels does occur, but the movement is usually limited.  Because mussels don’t have vision, lateral movements can seem random and be multidirectional.  In some locations where ice can occur attached to the substrate (anchor ice), mussels may move vertically, burying into the substrate during the winter, and moving to the surface in the spring.  Vertical movements during the spring to early fall may also be related to reproduction or a response to disturbance by other animals, predators or people.  Lateral mussel displacement due to high flows or dislodgement due to predators or human activity also likely occurs.  Mussel larvae have a parasitic phase where they attach to a host fish and can be moved by that host within the aquatic system.