Zebra mussels (Dreissena polymorpha) are a small, freshwater bivalve mollusk and a significant invasive species worldwide. Native to the lakes of southern Russia and Ukraine, they were accidentally introduced to new regions, primarily through the ballast water of transatlantic ships. Their first U.S. appearance was in the Great Lakes region in the late 1980s. Since then, they have spread extensively, causing widespread ecological disruption and economic losses. This article explores the various ways zebra mussels negatively impact both natural aquatic environments and human activities.
Ecological Consequences
Zebra mussels are efficient filter feeders, siphoning large volumes of water to consume microscopic plankton. This intense filtration increases water clarity, which drastically alters the natural aquatic ecosystem. The removal of phytoplankton and zooplankton from the water column depletes the primary food source for many native species, including larval fish and invertebrates, disrupting the base of the food web.
Their feeding and waste production alter nutrient cycling within invaded water bodies. Zebra mussels excrete nutrients, particularly phosphorus, in a form that promotes the growth of certain algae on the lake bottom, rather than in the water column. This shift can lead to increased harmful cyanobacteria blooms, such as Microcystis, even in environments with low nutrient levels.
Zebra mussels outcompete native filter feeders for food and space. They attach to native mollusks in large numbers, interfering with their ability to move, feed, breathe, and reproduce. This physical encrustation and competition can lead to severe declines and extinctions of native mollusk populations, with some populations crashing within four years of zebra mussel colonization.
Dense zebra mussel colonies on lake and river beds modify the physical habitat. Their presence changes the substrate composition, impacting fish spawning grounds and living spaces for invertebrates. This habitat alteration contributes to the decline of native species that rely on specific substrate types for their life cycles.
Infrastructure and Economic Impacts
Zebra mussels attach to almost any hard surface using byssal threads, leading to extensive biofouling. They form dense colonies on structures such as water intake pipes, boat hulls, docks, and industrial equipment. This adhesive ability creates problems for human-made infrastructure.
Their prolific attachment causes issues for water systems, including power plants, industrial facilities, and municipal water treatment plants. Zebra mussels clog intake pipes, restricting water flow and leading to increased maintenance costs and operational shutdowns. The power industry alone faces costs estimated at tens of millions of dollars annually for maintenance related to mussel clogs, with temporary shutdowns costing thousands of dollars per hour.
Boating and recreational activities are affected by zebra mussel invasions. The mussels attach to boat hulls, engines, and fishing gear, causing damage, reducing fuel efficiency, and necessitating costly cleaning and repairs. Their sharp shells accumulate on beaches, making recreational areas unpleasant and posing a hazard to bare feet.
The economic burden imposed by zebra mussels is considerable, encompassing management, cleaning, and repair efforts, along with lost revenue for affected industries. Estimates for the total cost of the zebra mussel invasion in the United States over a decade have reached billions of dollars. States like Montana project hundreds of millions in annual damages if mussels infest their waterways.
Beyond recreational and industrial impacts, zebra mussels affect agriculture. Their ability to clog pipes extends to irrigation systems, impeding water delivery to crops. This leads to increased operational and maintenance challenges for farmers, increasing costs for water delivery.
Preventing Their Invasion
Preventing the spread of zebra mussels relies on careful practices by individuals and coordinated efforts. The “Clean, Drain, Dry” protocol is a primary method for recreational water users. This involves inspecting and removing all visible aquatic plants, animals, and mud from boats, trailers, and fishing gear before leaving a water body.
After cleaning, drain all water from boats, including bilges, livewells, and engine cooling systems. This step removes microscopic mussel larvae, known as veligers, which are not visible. Allowing all equipment to dry completely for several days before entering another body of water helps ensure any remaining mussels or larvae are eliminated. Hot water rinses can also contribute to this process.
Public awareness and education campaigns inform water users about the threat of invasive species and prevention methods. These campaigns utilize media to reach boaters and other individuals who frequent aquatic environments.
Regulations and inspections are implemented by state and federal agencies to manage the spread of zebra mussels. These programs include mandatory boat inspections at launch sites, monitoring for early detection, and regulations governing watercraft movement between bodies of water. Individuals should avoid releasing unused bait or aquarium contents into natural waterways, as this can inadvertently introduce invasive species.