Speeded up 10 times, this video emphasizes that quagga mussels are active animals--much more active than washed up shells on a beach would suggest.
Quagga mussels and zebra mussels feed by filtering tiny plant and animal plankton out of the water and extracting the nutrients they need. Material they don't digest is wrapped in mucus and expelled. This "pseudofeces" is rich in nutrients like phosphorus.
Each tiny mussel filters a quart of water each day. That vigorous activity, abetted by circulating water, has effectively filtered the entire volume of water in Lake Michigan and other Great Lakes.
In the Great Lakes, invasive quagga and zebra mussels deposit their waste in the relatively narrow bottom areas near shore, where the mussels live. This has caused two profound changes to the lakes: It has dramatically cleared the water, and it has concentrated nutrients like phosphorus near shore. As a result, phosphorus concentrations have decreased off-shore and increased near shore, and sunlight penetrates deeper into the water.
Among the many consequences to the lake's food web are a major shift of energy sources (phytoplankton) away from open waters, where they would ultimately support trout, salmon, and whitefish, and an increase in nutrients like phosphorus available to algae growing near shore.