This Wisconsin Public Television segment introduces you to our friend, the quagga mussel, the invasive species from Europe.
WHAT IS IT
The quagga mussel (Dreissena rostriformis bugensis) is a subspecies of freshwater mussel, an aquatic bivalve mollusk.
This subspecies is indigenous to the Dnieper River drainage of Ukraine. The species is named after the quagga, an extinct subspecies of African zebra, possibly because, like the quagga, its stripes fade out towards the ventral side.
APPEARANCE
The quagga shell is striped like the zebra mussel's shell, but the quagga shell is paler toward the hinge. There is a large range of shell morphologies, including a distinct morph in Lake Erie that is pale or completely white.
The quagga is slightly larger than the zebra mussel, about 20 millimetres (0.8 in) wide, roughly about the size of an adult human's thumbnail and has a rounded carina and a convex ventral side.
DIET
Quagga's are filter feeders, they use their cilia to pull water into their shell cavity where it passes through a siphon which removes phytoplankton, zooplankton and algae.
Each adult mussel is capable of filtering one or more liters of water each day.
Undesirable material in the water is bound with mucus, known as pseudofeces, and ejected out the siphon. This particle-free water is then discharged out the excurrent siphon.
REPRODUCTION
Due to their prolific breedering through external fertilization, quagga's are capable of spreading quickly in an ecosystem.
A fully mature female quaggga is capable of producing up to one million eggs per year. After fertilization, microscopic larvae, or veligers, develop within a few days and these veligers soon acquire minute bivalve shells.
Free-swimming veligers drift with the currents for three to four weeks feeding by their hair-like cilia while trying to locate a suitable substrate to settle and secure their byssal threads on.
Mortality of these young quagga may exceed 99% as they search for a stable home.
INVASIVE SPECIES
The introduction of both zebra and quagga mussels into the Great Lakes appears to be the result of ballast water discharge from transoceanic ships that were carrying larvae or adult mussels.
The quagga mussel was first observed in North America in September 1989 when it was discovered in Lake Erie near Port Colborne, Ontario. It was not identified as a distinct species until 1991.
Since their arrival in Lake Michigan, quagga's have all but replaced the zebra mussell as the dominant invasive species.
The quagga's arrival has also lead to numerous disruptions of both the Lake Michigan food web and has had an economic impact on Milwaukee due to the following factors:
- Quaggas water filterering removes substantial amounts of phytoplankton and suspended particulate from the water which decreases the food source for zooplankton, the building block of the Lake Michigan food web.
- The water filtration increases the water's transparency, water clarity increases light penetration causing a proliferation of aquatic plants that can change species dominance and alter the entire ecosystems.
- Pseudofeces produced from filtering the water accumulates and as the waste particles decompose, oxygen is used up, and the pH becomes very acidic and toxic byproducts are produced.
- Quagga's accumulate organic pollutants within their tissues to levels more than 300,000 times greater than concentrations in the environment and these pollutants are found in their pseudofeces, which can be passed up the food chain, therefore increasing wildlife exposure to organic pollutants.
- Quagga's ability to rapidly colonize hard surfaces causes serious economic problems as they can clog water intake structures, such as pipes and screens, therefore reducing pumping capabilities for power and water treatment plants, increasing up keep costs which increase the cost to the community.