There are many ways that zebra mussels are able to spread from place to place. Some of the most common means of mussel movement are discussed below. There are naturally occurring vectors of dispersal and there are human-mediated means. Human-mediated means of dispersal tend to occur on a larger scale and over a longer period of time. There is very little chance that enough zebra mussels could be moved by a naturally occurring vector to establish a substantial population. At present, researchers are trying to better understand many of these natural conduits, but there is at least anecdotal evidence to support all of the natural means of dispersal, which are included in the list below.
Boats
If a boat has been in an infested body of water, it may have adult mussels attached to it. Mussels may be on the bottom, in the intake pipes for the engines, in the bilges, or on any other surface that is wet and comes into contact with raw lake water. Once the boat is transported to an uninfected body of water, the mussels may migrate off the boat and into the new habitat.
Even if adult mussels are not visible on a boat or other piece of equipment that has been in contact with infected water, very small juvenile mussels (1-3 mm) may be attached. Any exchanges of water between an infected area and an uninfected area (i.e., ballast exchange, pumping of bilge or pumps, bait buckets) can potentially transfer larval mussels. It's a good idea to rinse any equipment thoroughly with fresh water when leaving an infected area.
· Aquatic plants
Adult zebra mussels will settle on and colonize submerged aquatic plants.
Note the colonization of mussels on this aquatic plant.
If plants are transported from an infected lake to an uninfected body of water, it is likely that adult zebra mussels may well be transported, too. Some possible means of unintentional transport include plants attached to boat trailers and plants in or on bait buckets or other fishing gear.
Water flow and larval drift
Larval zebra mussels (see the Life History and Biology section for more details), are free-swimming, microscopic, and planktonic. These factors contribute to their rapid spread from one body of water to another. Any body of water downstream of an infected area has a high probability of being infected if there is continuous water flow from the upstream area.
Ducks or other aquatic water fowl
It is not unusual to see large increases in waterfowl populations after the invasion of zebra mussel in a body of water.
Substrates with high densities of zebra mussels in shallow areas are the preferred foraging areas, and these mussel colonies can be located rather quickly by migrating waterfowl. Migrating waterfowl may carry larval or juvenile mussels in their feathers or on their feet, but it is highly unlikely that they disperse mussels from one waterbody to another.
Crayfish
These crustaceans can be the site of zebra mussel settlement. If they are moved from an infected area to an uninfected area after settlement, but prior to their molting event, it is possible that they could transport mussels.
Zebra mussels will colonize on any suitable substrate including this crayfish. If a crayfish containing zebra mussels is introduced into an uninfested waterbody, a new population could be established.