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 The threat from quagga & zebra mussels

A mussel update on Electric Lake and Red Fleet Reservoir.

Paul Birdsey
Paul is the aquatics manager in the DWR's Southeast Region. He describes himself as the world's only limnologist, planner, database programmer, hypersaline system ecologist, financial manager and fisheries administrator. In his free time, Paul can usually be found fishing.

ZEBRA AND QUAGGA MUSSELS are small (0.25–1.5 in) bivalve mollusks originally native to Russia. According to Wikipedia, zebra mussels were first found in Lake St. Clair, Michigan in 1988. Quagga mussels were first identified in Lake Erie a year later. The discharge of ballast water from ocean going ships is thought to be the most likely way these invasive species were transported to the United States.

Quagga and zebra mussels

On the left, a quagga mussel. On the right, a zebra mussel.

Since their initial invasion into the Great Lakes region, zebra and quagga mussels have spread rapidly throughout much of the country east of the 100th meridian. No mussels were found west of that line until 2007 when quagga mussels were discovered in Lake Mead, Nevada.

Following the discovery in Lake Mead, intensive sampling was undertaken by the western states. Mussels were identified from Lake Havasu and Lake Mohave in Arizona in 2007. California reported infestation of several lakes in 2008 as did Colorado and Utah the same year. The likely method for transportation of invasive mussels to these waters was recreational boats.

Zebra mussels and the closely related quagga mussels reproduce quickly and can have devastating impacts to aquatic ecosystems. They are efficient filter feeders and can effectively remove large quantities of phytoplankton from the water. Because phytoplankton forms the base for many food chains in a lake, a cascading collapse of the entire food web can then result. Most often, this collapsing food web is noticed by casual observers as increased water clarity and may be incorrectly viewed as a benefit of the mussel invasion until the underlying mechanism is understood.

Other detrimental effects of zebra and quagga mussels include blockage of water delivery systems by large masses of mussels, dead shells lining beaches which cause the beaches to be virtually unusable, and odor problems along shorelines created by the decomposition of dead mussels. All of these problems have resulted in millions of dollars worth of cleanup efforts in the Great Lakes area and made some recreational beaches unusable.

The Utah Division of Wildlife Resources launched an intensive detection and containment program after quagga mussels were discovered in Lake Mead. Five biologists were hired statewide with the responsibility of coordinating monitoring efforts and supervising decontamination technicians at various waters. The technicians are charged with interviewing pre-launch boaters and washing any suspect boats with high pressure hot water to prevent infestation with mussels.

Since it may take years for enough adult mussels to show up in a system to be observed; detection efforts in Utah rely on using fine meshed plankton nets to collect the microscopic larvae of the invasive mussels. Plankton samples are collected by the biologists throughout the summer months and sent to a laboratory for microscopic examination. Suspect organisms from the microscopic examination are forwarded to a second laboratory for DNA analysis.

Using this procedure, two lakes in Utah were identified as being infested with invasive mussels in 2008. Quagga mussel larvae were identified from Red Fleet Reservoir near Vernal, and zebra mussel larvae from Electric Lake near Huntington. Several other lakes were inconclusive, meaning that something suspicious was observed under the microscope, but could not be verified with DNA analyses.

Electric Lake sampling

Aquatics biologist Dan Keller inspecting for mussels on an Electric Lake outlet structure

Dozens of samples have been taken from Electric Lake and Red Fleet since the initial finding of invasive mussel larvae in 2008. All of the samples from both reservoirs have been negative for both the microscopic examination and follow-up DNA testing. The DWR has also inspected all docks, outlet works, and other structures in both reservoirs for adult mussels with negative results.

So why have we not been able to find them again? There are several possible explanations. First, it is possible that we happened to sample shortly after an initial inoculation of larvae into the reservoir that did not subsequently produce breeding adult mussels. Another possible explanation is that the density of larvae in the reservoirs is still very low and that, despite intensive sampling, we have not detected them again. Information from Kansas suggests that this is possible. A reservoir there was initially detected as being infested with quagga mussels, then there were five years of negative results before adults were finally found. Finally, although slight, there is always the possibility of human error in either the sampling or laboratory analyses. Great care is taken in both the field and the lab to ensure this does not happen, but it cannot be completely eliminated as a possibility.

Where do we go from here?

The DWR will continue intensive sampling at both Red Fleet Reservoir and Electric Lake through 2011. If we do not detect any adults or larvae in our 2011 samples, both reservoirs may be downlisted from their current detected status. Sampling will still occur, and boaters at both reservoirs will be encouraged to either have a professional decontamination or self-decontaminate, but it will not be required.

Invasive mussels continue to be the single greatest threat to aquatic ecosystems. Every boater in the state should practice the Clean, Drain and Dry method of self-decontamination every time they boat, regardless of the official status of the water. Failure to do so could result in millions of dollars in damage to water delivery systems and the collapse of fisheries and loss of other recreational opportunities. More information on the threats of invasive mussel and boat decontamination procedures can be found at StopTheMussels.org.

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