DNR: More zebra mussels found in Iowa Great Lakes

Thursday, December 20, 2012
Pictures from other lakes demonstrate how zebra mussels can take over a habitat. Iowa DNR officials are concerned because three juvenile zebra mussels were collected at East Lake Okoboji in December. (Photos submitted)

The Iowa Department of Natural Recourses on Tuesday said three juvenile zebra mussels were found attached to docks and hoists removed from East Okoboji Lake.

Biologists say the discovery increases "the likelihood that the invasive species may be establishing itself in the popular northwest Iowa chain of lakes."

"We're not going to declare an infestation because these things do happen," said Mike Hawkins, Spirit Lake District fisheries management biologist. "You see isolated incidents or isolated animals and they don't take off and they don't form a naturally-reproducing population -- they kind of fizzle out. So, we are seeing very, very early indications of zebra mussels and -- absolutely -- there's always a possibility that this could fizzle out. There is some hope still."

The DNR says zebra mussels are native to the Caspian Sea region of Asia and were introduced into the North American Great Lakes in the 1980s from ballast water of oceangoing ships. They have spread throughout lakes and rivers in the Midwest and around the country.

Known populations of zebra mussels in Iowa include Clear Lake, Lake Rathbun, the Mississippi and Maquoketa rivers, and Bluebill Lake near Mason City, according to the Iowa DNR.

"We can look at other lakes where infestations have occurred and kind of draw from those experiences," Hawkins said. "We will have some varied impacts, depending on what lake we're talking about. We have a complex chain of lakes here."

In general, the DNR has seen what Hawkins calls "energy shifts in the ecosystem."

"Zebra mussels are tremendous water filterers," he said. "They can filter large quantities of water, and what they are removing are plankton and zooplankton from the water. They're feeding on those micro-organisms. That changes what's available for the rest of the plants and animals out there. In many cases, we have seen or have documented increased water clarity -- increased water clarity sounds like a good thing, but in some cases that can be accompanied by greater blue-green algae blooms."

It also changes the available food for larval fish and other native species in the Iowa Great Lakes. Increased plant growth also is possible.

"From a recreational standpoint, these organisms can explode their numbers -- at least initially," Hawkins said. "We may see some subsequent die-offs in zebra mussels. That's when their shells -- washing up on shorelines and beaches -- can cause some impacts to folks who want to use the water. They'll want to take some precautions to keep their feet safe because the dead shells can be very sharp."

If densities are high enough, zebra mussels can smother native mussels by attaching to their shells. Water utility providers in the Iowa Great Lakes also could see some impact.

"It shouldn't affect drinking water, but it changes the way those drinking water utilities have to do business -- what precautions and steps they have to take to keep their intakes from becoming plugged," Hawkins said. "The mussels will colonize the insides of pipes and block the intakes. There are ways to manage that and those utilities are already working toward implementing those measures."

Hawkins said the Spirit Lake Fish Hatchery staff also will have to makes some adjustments.

"We supply walleye, walleye fry, muskie and northern for many places in Iowa and there is going to have to be some work done here at the hatchery to make sure we don't transmit or move zebra mussels at the same time we're moving fish," he said.

Hawkins credits the Iowa Great Lakes community for providing important leadership to the state of Iowa in fighting aquatic invasive species. The strong partnership between state and local officials remains "our best weapon against these invaders," he says. Biologists have yet to identify a way to eradicate or control zebra mussels once they have infested a lake.

"Much will be learned over the coming year, I think," Hawkins said. "We'll start to see either no further evidence or we'll start to see further evidence of an infestation."

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