Written by Industry Expert Kara Sliwoski, Aquatic Biologist
Zebra mussels (Dreissena polymorpha) are an increasingly problematic invasive species found throughout North American waterbodies and waterways. They are a small shellfish, regularly the size of a dime, that can grow to almost two inches in length, at their largest. Their namesake comes from the striped pattern typically exhibited on their shells. However, shell patterns can vary significantly between individuals and in some instances the mussels can have no stripes at all.
Native to Russia, zebra mussels are believed to have been introduced into the Great Lakes via ballast water from a visiting ship in the mid-1980s. They prefer colder freshwater habitats, but have also been found in slightly saline environments. Since their introduction, zebra mussels have spread throughout the Great Lakes and into the Ohio and Mississippi River basins, which is their primary area of distribution. To date, zebra mussels have been documented in at least 28 states and over 600 waterbodies; locations range from western New England to along the Missouri River in South Dakota and along the Arkansas River in Kansas. Unfortunately, there are scattered locations gradually appearing as far west as California as well.
Zebra mussels are prolific invaders with the ability to spread quickly within a waterbody. During a single spawning season an individual female mussel can produce more than one million eggs. After a short free-swimming phase, the juvenile zebra mussels begin to settle on the bottom, attaching themselves with thread-like structures to hard surfaces such as rocks, boat hulls, water intake pipes and even shells of native mussels. The mussels colonize in densities ranging from 300,000 to 1,000,000 individuals per square meter, often covering and encrusting suitable surfaces. This undesired underwater accumulation, referred to as biofouling, is one of the major problems associated with zebra mussels. Biofouling easily becomes a spreading mechanism for this aquatic hitchhiker if boats are used between infested and un-infested waters.
Water intake pipes (used for irrigation, drinking water and power plants) are especially vulnerable and affected because they provide zebra mussels with protection and continual water flow with food and oxygen. Dense colonies reduce intake volume and pipe flow and, in extreme cases, can completely clog intake pipes. Zebra mussel infestations can also lead to accelerated pipe corrosion and potential issues with noxious odors and tastes. Inevitably, these impacts can result in large economic consequences if not addressed appropriately.
Zebra mussels are also detrimental to native mussel populations; they frequently outcompete other filter feeders for resources such as food and habitat space. Native mussels are usually larger in size than zebra mussels are, which allows zebra mussels to colonize on the shells of native mussels. Usually, when a native mussel has a zebra mussel attached, the native one is unable to move, feed and breed. This colonization makes the native mussels more prone to environmental stressors, and there is concern that rare native mussel species may be completely eliminated from some waterbodies as a result.
Zebra mussels are tremendously efficient filter feeders and an individual mussel filters up to one liter of water per day; this constant filtering can result in significantly increased water clarity. Although improved water clarity may be seen as beneficial by some recreational lake users, large zebra mussel populations filter out microscopic organisms leaving less food for small and juvenile fish, invertebrates and other competing filter feeders resulting in an unbalanced food chain and ecosystem, and significant loss of fishery productivity. Increased water clarity also allows more sunlight to reach further into the water column, which can encourage more and deeper growing aquatic plant growth. Aquatic vegetation is necessary for a healthy waterbody, but too much growth can become a nuisance and hinder recreational uses. Additionally, invasive plant species can tolerate lower light, so increased water clarity encourages new infestations in deeper waters than had previously existed.
Although few tools are currently available for zebra mussel management, SOLitude is able to provide those tools to help. There are some newer molluscicides showing positive results that are currently available for use; however, use is highly state regulated and dependent as the pesticide must first be registered for use in that state. If permitted by the state, SOLitude is equipped to perform both large or small scale treatments taking the necessary steps before and after treatment to ensure proper application.
Though significant investment in research for zebra mussel management has resulted in the introduction of a few suitable pesticides, their use is limited due to concerns for impacts on native aquatic organisms. Currently, prevention is the best management tool against zebra mussel invasion. The zebra mussel’s ability to attach to smooth surfaces such as boat hulls is one of the reasons they are so successful at spreading between waterbodies. Before entering and after exiting a waterbody boats, trailers and accessory equipment should be inspected to remove plants and organisms to prevent any zebra mussels (or other invasives) from entering or spreading within waterbodies. This includes draining all bilge, live wells, bait buckets and other waters from the boat, ideally on land and away from any waters; the same technique applies to extra bait, as no organisms should ever be released, unless obtained from the site. If possible, wash down all equipment with hot water and let it thoroughly dry for at least 5 days before using again; if the equipment is needed sooner, disinfecting everything with a bleach solution is the best option. This action plan (inspect/clean, drain, dry/wash) should always be performed before and after using a boat and related equipment, but is especially true and important when used in zebra mussel infested waters.
Ultimately, if a new zebra mussel infestation is thought to be found, please notify the appropriate local state agency, as an emergency response protocol may already be in place. If zebra mussels are in nearby waters, it is imperative to be educated on identification and prevention of these (and other) aquatic hitchhikers.
Just remember, though zebra mussels may be insignificant in size, they are significant in impact.
Contact the experts at 888-480-LAKE (5253) for all of your lake, pond and fisheries management needs.
Kara Sliwoski is an Aquatic Biologist with SOLitude Lake Management. Kara earned her Bachelor of Science degree in Marine Biology and Environmental Science from Roger Williams University in Bristol, RI in 2015 and is responsible for assisting in chemical applications, vegetation surveys, report and proposal writing for clients, ArcGIS mapping and dive tending for hand harvesters.
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