Every month, we will put a spotlight on an aquatic invasive species (AIS) in a re-occurring monthly article. Check it out! This month, we highlight a well known invasive species: zebra mussels!
Zebra Mussels
Zebra mussels (Dreissena polymorpha) have become one of the most recognizable aquatic invasive species and perhaps the most infamous. Invasive species are non-native and harm the economy, the environment, or human health. Zebra mussels have negatively impacted not just one of these topics, but all three in a massive and visual way that gains the attention of news outlets and lake users across the country.
Zebra mussels are small shellfish (1/8 in – 2 in) and are fairly distinguishable from native shellfish. The zebra mussel gets its name from the
Zebra mussel cluster. Photo taken by D. Jude, Univ. of Michigan.
stripped pattern on its shell that resembles the coat of a zebra. These mussels will attach to any hard surface by byssal threads. There are no native shellfish in North America that have byssal threads.
Native to the Black, Caspian, and Azov Seas in Eurasia, zebra mussels were first documented in North America in 1988 in Lake St. Clair. It is believed that a release of larval zebra mussels occurred during a ballast water exchange of a cargo ship that was traveling the St. Lawrence Seaway. Following the initial discovery, a rapid number of findings were reported. By the end of 1989 zebra mussels could be found in all five Great Lakes. In Wisconsin, zebra mussels have become established in 272 lakes and rivers which is less than 5% of Wisconsin’s over 15,000 lakes. The Winnebago System were invaded by zebra mussels in 1999.
Zebra mussels have several traits that make their dispersal both within a lake and overland between lakes extremely successful. Male and female mussels release their eggs and sperm into the water similar to the way coral reefs reproduce. In a single year, every zebra mussel female will release over one million eggs! Once consummated, the microscopic veliger form of the zebra mussel free-floats in the water as it eats and starts creating a calcium carbonate shell. The veliger usually remains free floating for several weeks before sinking.
Zebra mussel. Photo Credit: Paul Skawinski
Depending on wind and water currents, zebra mussels can be spread across lakes or through rivers very easily. After sinking, zebra mussels attach to any hard surface which can include rocks and submersed aquatic plants, as well as boats, anchors, and buoys. If boats are then trailered to new locations, zebra mussels can hitchhike across great distances between lakes that have no water connection. Boats also tend to have places that do not fully drain or that are designed to hold water. For instance, if zebra mussel veligers are sucked up into a boat’s livewell, bilge, or motor, they can stay alive and potentially be transported to new waterways.
Once zebra mussels become established in a waterway, they can negatively impact the environment, human health, and the economy. Zebra mussels filter feed; they draw water into their bodies and filter out food particles such as algae. Each zebra mussel can filter over a liter of water per day. This filter feeding can result in short-term increases in water clarity but depletes the algal food source which it the base of the aquatic food web. With sunlight able to reach deeper depths in the waterbody, more rooted aquatic plants can grow. If a lake has both zebra mussels and Eurasian watermilfoil (EWM) or curly leaf pondweed (CLP), oftentimes the EWM or CLP will colonize the new areas where sunlight reaches.
While zebra mussels feed on algae, they are able to selectively feed meaning that they don’t eat all types of algae. For instance, they do not eat blue-
Zebra mussels on buoy.
green algae. So as zebra mussels remove native algae from the water and these nutrients are released back into the water, blue-green algae numbers can increase since the algae can use the nutrients and is not eaten by the mussels.
In addition to filtering out a large portion of the base of the food web and changing the ecosystem, zebra mussels can also negatively impact waterways through sheer numbers. Since zebra mussels can produce over 1 million eggs every year, populations of mussels can increase at exponential rates and are limited by the amount of food, the number of hard surfaces in the system, and the amount of calcium in the invaded waterbody (since calcium is need to create a shell). In fact, there are cases of zebra mussels attaching to the shells of native mussels in such high densities that the native mussels are essentially smothered to death. Densities of zebra mussels have reached as high as 100,000 in 10.5 ft2! Once zebra mussels die, their shells are washed up on beaches where they are sharp enough that they can cut the feet of people as they walk over them. Swimmers also cut their feet on mussel shells if they are swimming in a rocky area with zebra mussels attached to the rocks.
With mussels attaching to any hard surface, the water supply pipes in invaded waterways often have zebra mussels attached to them. The water intake pipes of power plants, public water supply plants, and other industrial buildings can get clogged with zebra mussels where little to no water is being drawn in through the pipe (a.k.a biofouled). In the Winnebago System where over 250,000 people get their drinking water from zebra mussel-invaded Lake Winnebago, it costs residents hundreds of thousands of dollars a year to clean out those pipes. Small mussels often get sucked into motors and can cause damage to the engine. Buoys and docks can become encrusted with zebra mussels and cause damage or even cause the buoys to be sunk due to the weight of the mussels! All of these impacts are felt to both local and national economies. A team of Congressional researchers estimated that zebra mussels cost over $5 billion to the U.S. economy in the period between 1993-1999. It has been estimated that the costs to manage mussels in the Great Lakes region exceeds $500 million annually!
In Wisconsin, zebra mussels are classified as restricted.
Want to help? HELP PREVENT THE SPREAD!
Every time you come off the water, make sure to follow these steps to stop the spread of faucet snails and other aquatic invasive species:
* Inspect boats, trailers, push poles, anchors, and other equipment for attached aquatic plants or animals.
* Remove all attached plants or animals
* Drain all water from boats, motors, livewells and other equipment
* Never move live fish away from a waterbody
* Never release aquarium plants or animals into your local waterways
Follow the Fox Wolf Watershed Alliance’s Winnebago Waterways Program on our Winnebago Waterways Facebook page or @WinnWaterways on Twitter! You can also sign-up for email updates at WinnebagoWaterways.org.
Questions? Comments? Contact Chris Acy, the AIS Coordinator for the Winnebago Waterways Program covering Fond du Lac, Calumet, and Winnebago Counties at (920) 460-3674 or chris@fwwa.org!
Winnebago Waterways is a Fox-Wolf Watershed Alliance program. The Fox-Wolf Watershed Alliance is an independent nonprofit organization that identifies and advocates effective policies and actions that protect, restore, and sustain water resources in the Fox-Wolf River Basin.
Photo Credit: D. Jude, Paul Skawinski
