The Mussels That Rocked the Lakes:
The Devastating Legacy of Zebra Mussels in the Great Lakes
The Great Lakes, a marvel of freshwater biodiversity and an essential resource for millions, have been irrevocably altered by some of the smallest invaders imaginable: the Dreissena polymorpha or commonly referred to as the zebra mussel and its close cousin, Dreissena rostriformis bugensis AKA the quagga mussel. These tiny bivalves, no bigger than a thumbnail, have triggered one of the most profound ecological overhauls in modern history. Their unchecked proliferation has fundamentally reshaped the Great Lakes ecosystem, demonstrating how even minute organisms can unleash monumental environmental and economic devastation.
Origin: Native to the Black and Caspian Seas in Eastern Europe and Western Asia. They arrived in the Great Lakes in the late 1980s via ballast water.
For decades, massive cargo vessels crisscrossed the Atlantic, using freshwater as ballast to maintain stability. Upon reaching their destination ports, this ballast water – teeming with microscopic life, including the larval forms of zebra and quagga mussels – was simply discharged. In 1988, the zebra mussel was first detected in Lake St. Clair, connected to Lake Erie. The quagga mussel followed a few years later, first identified in Lake Erie in 1989, and has since proven to be even more ecologically dominant in many areas, particularly in deeper, colder waters. The St. Lawrence Seaway, an engineering marvel that opened the Great Lakes to global shipping, unwittingly became a superhighway for these aquatic hitchhikers.
What makes these mussels such formidable invaders?
Their success hinges on several key biological traits like their prolific ability to reproduce. A single female zebra mussel can produce up to a million eggs per year. These eggs develop into microscopic, free-swimming larvae called veligers, which can drift with currents for weeks before settling. People notice how clear the water in many of the Great Lakes looks in the past decade. That is in part due to their ability to efficiently filter as they feed. They possess highly efficient siphons that allow them to filter vast quantities of water, removing phytoplankton, zooplankton, and other suspended organic matter.
They have an uncanny ability to stick to anything in the water. Using specialized structures called byssal threads, they can securely attach to virtually any hard surface – rocks, pipes, boat hulls, native mussels, even each other, forming dense, multi-layered colonies. This allows them to quickly colonize new areas and withstand strong currents.
Their ability to inhabit so many different ecosystems comes down to the fact that they are ecological generalist. They can tolerate a wide range of environmental conditions, though quagga mussels are particularly adaptable to colder temperatures and deeper waters, allowing them to expand their range even further than zebra mussels.
The Ecological Fallout of the Zebra Mussels: What Harm Are They Doing?
The harm caused by zebra and quagga mussels is multifaceted, rippling through the entire Great Lakes ecosystem from the microscopic level to top predators, and impacting human infrastructure.
Food Web Devastation: A Bottom-Up Cascade
Their most significant ecological impact stems from their insatiable appetite. By filtering enormous volumes of water, they strip out the phytoplankton and zooplankton that form the base of the aquatic food web. Imagine a landscape where the primary food source for almost every animal suddenly vanishes. That’s the scale of disruption.
“They’ve essentially re-plumbed the system,” explains Ashley Elgin, a Research Scientist with NOAA’s Great Lakes Environmental Research Laboratory (GLERL), a leading expert on mussel impacts. “By removing so much of the plankton, they’ve diverted energy away from the open water column to the lake bottom.” This “re-plumbing” means less food for native filter feeders, such as native mussels and certain planktivorous fish (like alewife and cisco), and less food for the entire food chain that relies on them. The decline in these forage fish, in turn, impacts larger predatory fish like lake trout and salmon, leading to a leaner, less productive fishery.
Water Clarity: A Deceptive Beauty
Visitors to the Great Lakes often comment on the increased water clarity since the mussels arrived. While visually appealing, this “clarification” is a double-edged sword. It’s a symptom of the plankton depletion. Moreover, clearer water allows sunlight to penetrate deeper, promoting the growth of nuisance aquatic plants in shallow areas. Paradoxically, while they filter most algae, zebra and quagga mussels can also selectively avoid ingesting harmful blue-green algae (cyanobacteria). They then excrete nutrients, effectively fertilizing these toxic algal blooms, which can become more severe and widespread. This means “cleaner” water doesn’t necessarily mean healthier water.
Habitat Alteration and Native Mussel Annihilation
Their ability to attach to any hard surface has led to massive changes on the lakebed. They form dense colonies, sometimes several inches thick, covering rocks, submerged logs, and even native species. Native mussel populations have been decimated, often smothered by layers of zebra and quagga mussels attaching directly to their shells, preventing them from feeding or moving. This loss of native biodiversity is a significant ecological blow.
Economic Burden: Billions in Damages
Beyond the ecological havoc, these mussels have inflicted an enormous economic toll. They clog water intake pipes for municipal drinking water systems, power plants, and industrial facilities. Their sheer numbers can reduce flow, decrease efficiency, and even cause system shutdowns. Maintaining and clearing these structures costs billions of dollars annually for communities and industries reliant on Great Lakes water. Boats, docks, and fishing gear are also frequently fouled, requiring constant cleaning.
Zebra Mussels encrust a boat’s propeller
The Ongoing Battle: Science on the Front Lines
Scientists like Ashley Elgin and others at institutions such as NOAA GLERL, the U.S. Geological Survey (USGS), and various Great Lakes universities (e.g., University of Michigan’s Cooperative Institute for Great Lakes Research – CIGLR) continue to study the long-term impacts of these mussels. Their work involves monitoring population dynamics, understanding nutrient cycling changes, and assessing the cascading effects on fish populations and food webs. While complete eradication is impossible given their widespread establishment, research focuses on management strategies, understanding their ecological interactions, and preventing further introductions of new invaders.
The zebra and quagga mussels serve as a stark reminder of the interconnectedness of our global systems and the profound, often unforeseen, consequences of introducing non-native species. They are a constant challenge, forcing us to re-evaluate how we manage and protect the precious resources of our Great Lakes.
