Sometimes, due to a lack of natural controls such as disease or competitors, a non-native species can easily become established in a new area. Once established, it can out compete and displace the native species, disrupting and degrading the environment. That’s an invasive species. And the zebra mussel is definitely invasive.
The zebra mussel is native to the Black, Caspian, and Azov Seas in Eastern Europe and Western Asia. It was probably brought to the Great Lakes in the ballast water of a cargo ship. When the ballast was emptied, the mussel was released also. It was first discovered in North America in 1988 in Lake St. Clair which connects Lakes Erie and Huron. By 1990, the zebra mussel was in all the Great Lakes. They have since been found in a number of lakes and river systems in about 30 states.
These are small animals, less than 2 inches long. The D-shaped shells of adults are yellow to brown and often striped in a dark and light pattern, hence the name zebra mussels. But they can also have mostly dark or light shells. The underside of the shell is very flat. Zebra mussels have a special organ, the byssus, which they use to attach themselves to things. The byssus produces threads which protrude between the two halves of the shell and attach to hard surfaces with a strong glue. Zebra mussels are usually found attached to objects or each other by these threads. They are the only freshwater mussel that can firmly attach itself to solid objects like submerged rocks, dock pilings, boat hulls, and water intake pipes.
Zebra mussels are filter feeders, meaning they suck in water, filter out the tiny plants and algae, and spit the water out again. They are really good at filter feeding, an adult can filter about a liter of water a day. They are also really good at breeding. A female can produce up to one million eggs during a spawning season. Zebra mussel larvae are microscopic and free-floating. They will drift in the water for three to four weeks. As they develop, the juveniles search for something to attach to. They prefer hard or rocky surfaces, but will attach to plants if necessary. They will also settle on other zebra mussels and on native mussels.
Why are zebra mussels a problem? They lack natural control mechanisms here in the U.S., such as an effective predator, and their populations can increase quickly. Plus, they are very easy to spread from place to place. The larvae can be present in bait buckets or live wells and released when this water is emptied. As they mature, they can attach to boats and be transported from place to place. Even if a mussel infested boat is taken out of the water, the mussels could survive. When it’s cool and humid, adult zebra mussels can live for several days out of water.
Adult zebra mussels are well known for their ability to clog water pipes. They attach and grow inside the pipes in such numbers that they severely restrict water flow. They have also sunk navigational buoys because so many mussels grew on the underwater surface. Fishing gear left in water for long periods can be ruined and boating can be affected due to the drag created by attached mussels. Zebra mussels can damage dock and pier supports. These mussels can cover any hard object in the water, including native mussels, eventually killing them. Zebra mussels are believed to be responsible for drastic reductions in native mussels.
Because they are such efficient filter feeders, they remove substantial amounts of algae from the water. This decreases the food available for the tiny aquatic animals and could impact the entire food chain, including the fish population. When there are large numbers of zebra mussels, they make the water more clear because they remove so much of the algae. While this may not seem to be a problem, it can increase the depth of light penetration into the water and cause a proliferation of rooted aquatic plants which couldn’t grow before due to lack of light.
Interestingly, zebra mussels do not eat blue green algae. What we call blue green algae is really a type of bacteria that captures energy from sunlight through photosynthesis, much like plants. These are the “algae” that can result in pea soup-like, scummy water. They can also produce toxins that are harmful to humans, pets, and wildlife. So, no, zebra mussels can’t solve problems caused by blue green algae.
Getting rid of zebra mussels is very difficult and expensive, so the best defense is to prevent their spread. To avoid spreading zebra mussels, boaters and others who enjoy water recreation should remember to CLEAN, DRAIN, DRY their equipment when removing it from the water. This includes boats, trailers, jet skies, waders, anything that comes in contact with the water. CLEAN off any plants, animals, or mud that you see. On land, DRAIN live wells, bait buckets, bilges, and any other compartments that hold water. If possible, allow equipment to DRY for at least five days before using it in a different body of water. Alternatively, you can pressure wash equipment with hot (140°F or hotter) water. Freezing temperatures will also kill the mussels, as will chlorine bleach and full strength vinegar.
Even if zebra mussels are not known to exist in your water, make CLEAN, DRAIN, DRY your standard practice. Infestations can go undetected and there are other aquatic invasive species – animals, plants, insects, and diseases – that you can prevent the spread of by practicing CLEAN, DRAIN, DRY.
This article was contributed by Bobbi Holm, UNL Extension Educator