The Quagga Connection

The Quagga Mussel (Dreissena bugensis) is a small, clam shaped, invasive mollusk from Eastern Europe that has significantly altered the ecology of Lake Michigan and the bay of Green Bay. Since their introduction into the Great Lakes in the late 1980s, quagga mussels have caused major changes to this aquatic ecosystem. One of the greatest eco-changes is the interaction with Cladophora (Cladophora fascicuaris), a harmless type of bottom dwelling, filamentous green algae native to the Great Lakes. This relationship has had profound ecological, economic, and health related implications. Our understanding of this interrelationship is crucial for devising effective management strategies.

Quagga mussels, native to the Dnieper River Basin in Eastern Europe, were first discovered in the Great Lakes in 1989. They likely arrived in the ballast water discharges from transoceanic ships. Their rapid spread across the Great Lakes has been attributed to their high reproductive capacity and adaptability. By the early 1990s, quagga mussels had established populations in Lake Michigan and the bay of Green Bay. Today’s quagga numbers are estimated to be near 750 trillion in Lake Michigan, living at depths to 540 feet.

Quagga mussels are filter feeders, consuming microscopic floating plankton, and filtering large quantities of water. They, collectively, can filter all of Lake Michigan’s water once a month. Their feeding behavior has led to a significant reduction in the abundance of essential phyto- and zoo-plankton, which includes a variety of organisms that form the base of the aquatic food web pyramid. This reduction has had cascading effects on all consumer levels of the aquatic ecosystem.

One of the key interactions is between the growing populations of quagga mussels and the rapid growth of Cladophora algal blooms. Cladophora thrives in nutrient-rich, sunlit environments. The decline in plankton, due to quagga mussel filter feeding, has led to increased water clarity, which benefits the Cladophora photosynthetically with the greater availability of sunlight causing algae to grow. Water clarity was more turbid before the 1989 Quagga invasion.  Visibility was low, fluctuating around 8-10 feet, however, today’s visibility is 80-90 feet! With more sunlight penetrating deeper into the water, Cladophora could now grow more abundantly on the increased, lit up surfaces of the lake bottoms. They also attached to the mussel shells themselves giving them even more solid surfaces to anchor upon.

The relationship between the quagga mussels and the Cladophora exacerbates phosphorus levels in the lake and bay. Phosphorus (P), usually found in the form of phosphates (PO3) is a key ingredient that drives algal blooms. When quagga mussels filter out and consume phosphorus rich plankton they indirectly increase the concentration of phosphorus in the area by releasing phosphorus rich waste products. More light penetration and more phosphorus along with warming temperatures encourages algae growth, which in turn can contribute to further nutrient cycling and further release of phosphorus from the sediments. This creates a feedback loop where phosphorus levels remain high, perpetuating algal growth. Storms, winds, and currents disturb and break up the long, stringy algae that then washes up and collects upon the shorelines where it dies and decomposes in a most noxious way.

The proliferation of Cladophora and quaggas has several economic and health consequences. Economically, the increased growth of these organisms can clog water intake pipes for municipal and industrial water users, leading to higher maintenance cost and potential disruptions in water supply. Health impacts are also significant. The dense mats of decomposing Cladophora can harbor harmful bacteria, such as E. coli, which reproduce at an exponential rate in the warm muck, posing a risk to human health through physical contact with contaminated sludge and water. Additionally, when large algae blooms die and decompose while still floating, the decomposition process requires so much oxygen that aquatic life struggles to breathe; potentially leading to die offs and fish kills. These oxygen depleted areas are called “dead zones. There is a known dead zone in the bay of Green Bay just off its east shore, near the border between Door and Kewaunee counties. This area has excessive nutrient input from sewage treatment systems and agricultural manure spreading practices which play a large role in the dead zone’s development.

Addressing the issues caused by Quagga mussels and Cladophora requires a multifaceted approach:

1.  Monitoring and research: Continued research into the biology and ecology of quagga mussels and Cladophora is essential. Understanding their life cycles, growth patterns, and interactions can help in developing targeted management strategies.

2.  Control measures: While eradication of quagga mussels is challenging due to their widespread presence and reproductive capabilities, some control strategies include the use of molluscicides, although these are often controversial due to the potential impacts on non-target species.

3.  Phosphorus management: Reducing phosphorus inputs into the lake and bay is crucial. This can be achieved through better wastewater treatment practices, better agricultural practices that minimize runoff, and regulatory policies aimed at controlling both point and non-point sources of phosphorus. Home owners must also help by controlling lawn fertilizer applications and using phosphorus-free fertilizers.

4.  Public awareness and policy: Engaging with the public and policy makers in understanding the issues related to controlling quagga mussel and Cladophora growth; engagement which will lead to more effective management strategies and support for the necessary funding and research to succeed.

5.  Restoration efforts: Efforts to restore native species and ecosystems can also help to rebalance the aquatic environment and reduce the impacts of this invasive species and algae blooms.

The Quagga Mussel / Cladophora connection in Lake Michigan and Green Bay has led to a major disruption of the natural condition, causing significant ecological, economic, and health challenges. Addressing these issues requires a combination of research, management strategies, and public engagement to mitigate the negative effects and restore balance to this vital aquatic ecosystem.

By Paul Leline, DCEC Board Member

Sources:

Egan, Dan. The Devil’s Element: Phosphorus and a World Out of Balance.

LaLiberte, Gina, WDNR. “What’s That Green Stuff in the Water and on the Beach?” DCEC sponsored lecture notes from Crossroads at Big Creek, Sturgeon Bay, WI. 7 Aug. 2024.

Wright, D.A. & Cummings, J. “Impacts of Invasive Mussels on Aquatic Vegetation and Water Quality.”  Environmental Science & Policy 114 (2020): 92-102.