Individually they are only the size of a dime but together they can wreak havoc on structures and water species.
Numbering 700,000 per square meter (that’s three-feet-by-three-feet) the mollusks affix themselves to any hard surface — manmade or natural.
Because of this tremendous suction power, they do not easily wash off boats, rocks, or water intake pipes.
Jason Goeckler is a biologist with Kansas Department of Wildlife and Parks, working out of the Emporia office. He has been following the infestation and devastation at El Dorado State Park and Lake. Goeckler was the expert U.S. Army Corps of Engineers turned to when a zebra mussel recently was found at Marion Reservoir.
Goeckler said a 15-year-old teen was flipping rocks at a campsite at Cottonwood Point and asked her father, who happens to be an employee of KDWP, if a zebra mussel was on the rock.
The mussel was the size of a fingernail.
It was confirmed that it was a zebra mussel and two more juvenile zebra mussels were found which means there are more.
“The immediate issue at Marion Reservoir is the water supply. These mussels can attach themselves to water intake pipes and clog them up,” he said, which would hinder water quality.
And, somewhat unique to Marion Reservoir, with the presence of the zebra mussels, the blue-green algae may increase which would lead to taste and odor issues to those who drink water from the reservoir.
The mussels filter water, up to a liter a day, to eat plankton. The filtering clears the water which could allow the blue-green algae to run rampant.
“Some people think it’s a benefit because the mussels do clear the water but they don’t clear tribidity (bacteria). Instead they consume zooplankton which also decreases the fish population,” Goeckler said.
With the reduction of plankton, sunlight can better penetrate the water which enhances the blue-green algae.
The water supply also is affected because the zebra mussels can actually stop or significantly reduce the flow of water through intake pipes, like the ones at Marion Reservoir that serve Hillsboro, Marion, and Peabody residents.
To remove the critters is costly.
On the fishery side, the mussel population can ruin fish habitats, Goeckler said.
“Biologists provide structures for fish habitat by placing cedar trees and other structures in the water,” he said. The limbs of the trees spread out, providing shelter and cover.
“The zebra mussels will attach themselves to those limbs, causing a mass instead of individual fingers for cover which upsets fish habitat,” Goeckler said, and in turn, upset spawning sites which leads to the reduction of fish populations.
They also reduce the size of the fish because they are reducing some of the fish food.
What are zebra mussels?
Native to the Black Sea and Caspian Sea in Europe, they arrived into the Great Lakes in 1988 in the ballast water of ships.
Since that time, man has brought the species into the Midwest where they have been established in Perry Reservoir, Cheney Reservoir, the Walnut River below the El Dorado dam, and Winfield City Lake. They also are common in other parts of the country.
Zebra mussels look like small clams, usually less than an inch long with a D-shaped shell. The shell usually is yellowish-brown with alternating dark and light stripes.
They use sticky byssal threads to attach tightly to any hard surface.
Nationwide, expenditures to control zebra mussels in water intake pipes, water filtration equipment, and electric generating plants are estimated at $3.1 billion over 10 years.
Females reproduce at an alarming rate of 100,000 per year.
The life span of zebra mussels are three to five years with the population routinely dying off.
However, not all of the population will die, leaving some to reproduce and repopulate as before.
Goeckler said it is not true that birds and ducks can transport them from one body of water to another.
“It is only through human movement that the mussels are transported,” he said.
Zebra mussels will attach themselves to boats, trailers, and can be in water dipped for transporting fish, etc., which is why it is so important for the public to be educated and aware.
Lessons from El Dorado
Since the 2003 discovery of zebra mussels at El Dorado, the population has seen a significant increase in density which is common with a new infestation.
Since the life span of the mussels is three to five years, the population will routinely die off and because the El Dorado population is fairly new, Goeckler said, many of the adult zebra mussels in the population are from the same 2004-05 birthing year and nearing the end of their lifespan.
An additional stressor to the population was unusual water conditions in 2007.
“During the spring of 2007, a 12-foot raise ensued followed by a six-foot drop in lake elevation during the summer,” Goeckler said. Low water conditions during the winter killed millions of adult zebra mussels, many of which were nearing the end of their lifespan.
The record inflows during the spring and summer occurred at the peak of zebra mussel reproduction, allowing juvenile zebra mussels to settle in the flood areas. As the lake level returned to conservation pool, those newly settled zebra mussels were stranded in the shallow water and were left to desiccate and die. With the return of normal water levels, the zebra mussels that survived the water fluctuation began to colonize.
As the population continues to evolve, the waves of die-offs won’t seem as significant, Goeckler said, because much of the population will not be of the same age and die at the same time, as was the case this year.
“Unless nature again provides a similar weather pattern, we do not foresee a die-off of this magnitude affecting both juvenile and adult zebra mussels,” he said.
There are predatory fish that will eat zebra mussels. Blue catfish were released in El Dorado Lake, not as a means to reduce the mussel population but to take advantage of the new resource and provide a new species of fish for recreational purposes.
Affects on recreation
With Marion Reservoir being the location for more than 400,000 people per year, recreational affects could be significant.
Zebra mussels have a sharp shell. If unprotected skin comes in contact with a shell, the skin will be cut.
The mussels also can attach themselves to boat hulls and motors, causing the motors to clog and malfunction.
However, the mussels are not poisonous and will not cause any ill effects.
Randy Just, a park ranger at El Dorado State Park and Lake, said he received a telephone call from the boss of a camper who said he was concerned about his employee who became sick from the mussels and had missed work. Just explained to the caller that the mussels are not toxic and the only ill effects from the species are lacerations from the sharp shell.
What is next for Marion?
Education, Goeckler said.
“Our focus is on an education campaign,” he said. “Minnesota has been wildly successful at not spreading these things, and they have 10,000 lakes.”
Minnesota has implemented strict laws with fees and blanketed the state with information about the pesky mollusks.
Currently it is illegal to transport live zebra mussels. If anyone is found with the mussels in their possession, those found guilty could be incarcerated for up to six months and incur a fine up to $5,000.
Zebra mussels cannot be controlled in the wild. Chemicals can be used to kill zebra mussels but they also could affect fish and native mussels.
The best way is prevention, Goeckler said.
When boats are removed from a body of water, they should be thoroughly inspected. Also inspect trailers, motors, anchors, skis, and all other equipment that was in the water.
Boats should be left out of the water for five days or powerwashed with 140-degree water or scrubbed with a 10 percent chlorine bleach and water solution.
Never take fish or plants from one lake and put in another.
Never dip bait buckets into a lake or river if it has water in it from another body of water.
Drain all water from boats, live wells, and bait wells.
Zebra mussel larvae are free-floating and microscopic which enables aquatic users to transport them between bodies of water without knowing it.