Window on the Lake: Clear Lake, What if?

What if quagga mussels were found in Clear Lake, ooh oh what then? But first, what is a quagga mussel and why is it important? The first thing to know is it's an invasive species. One that has found its way to a new environment and is causing trouble. The Quagga is a species of Dreissena mussels that includes the Zebra mussel. Both the Quagga and the Zebra are about the size of a thumb nail and have two shells, like a clam. They originated in the Black Sea and developed an ability to survive in the fresh water of the Dnipro River in Ukraine. They spread by shipping during the 1940's and are now throughout Europe. In 1989, they were found in the Great Lakes probably coming by ballast discharges from ships bringing European goods. Unfortunately, they like their new home, are prolific, and a female can produce one million eggs per year which become veligers that attach to hard surfaces and then grow to adults. Now, both Quagga and Zebra mussels are spreading throughout the U.S.

Dreissenid mussels can foul water pipes, screens and pumps. They are filter feeders and millions X millions can inhabit a water body with each filtering a liter of water per day of particulates reducing the nutrient source for the food web. Organic pollutants and phosphorus can also be concentrated resulting in an increase in cyanobacteria and food chain contamination. The lake might appear clearer but a collapse of fisheries and bird populations have been recorded in many lakes.

So, if these unwanted species are found in Clear Lake what can we do? This question came up when the alarm bells were sounded in 2007 that mussels were found west of the

100th Meridian and specifically in Lake Mead. All water-bodies with mussels are quarantined and the spread has slowed but can they occur in Clear Lake and what can we do if they are found?

To answer these questions several years ago the County Director of Water Resources asked me as a consultant to determine a path forward. I teamed up with a professor at UNLV who was a recognized invasive species expert to conduct some water laboratory experiments on the shores of Lake Mead. Here, mussels already inhabiting the lake can be used to find some answers. I began by using a water tank truck to bring Clear Lake water and lakebed sediments to the Lake Mead laboratory. There, several aquarium tanks containing local Quagga mussels were lined up and different percentages of turbidity from Clear Lake sediment was added to see how the little filter feeding mollusks could handle it.

The idea for this approach came from reviewing documents on the spread of mussels from the great lakes. They do well in fairly clear water of the Mississippi River but are not found in high turbidity areas. The Lake Mead lab results indicated that even adult mussels had 100% mortality in highly turbid waters within a few hours. The results and details of the study are found in a peer reviewed paper published in the Book “Biology and Management of Invasive Quagga and Zebra Mussels in the Western United States (2015).” Other tests were also conducted that compared the growth rates of mussels and new veligers in Clear Lake water against those in Lake Mead water. Clear Lake water with its higher nutrient values was the leader by far.

Using this information, a plan was suggested that placing stations around Clear Lake could determine an early stage infestation. These were to be countered with a pontoon boat using a suction dredge (much like stream mining for gold) to pull bottom silt into the top water column increasing the turbidity to saturation for several hours. Placing a floated water curtain around the area to contain the effect was an added step. Any additional anti mussel liquids could be added to the discharge stream.

The bottom line is that Clear Lake as a shallow natural lake with a sediment bottom may have an answer other lakes can't duplicate. So what if, does have an answer.

—Jim Steele is a former Biological Consultant, former Lake County Supervisor, retired Branch Chief for CA Fish and Game and taught environmental science courses at CSUS.