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Zebra mussels plague region's waterways

Invasive mollusks clog water systems, wipe out plankton, other species.

Friday, June 17, 2011 - 10:43 am

Since the first zebra mussel larvae were sucked into the ballast tanks of a freighter on the Caspian Sea, then jumped ship into the Great Lakes in the 1980s, the small mollusk has wreaked havoc on the inland waters of the United States.

In Kosciusko County, the mussels have been discovered in 19 lakes, including Syracuse, Webster, Winona and Big Barbee. In LaGrange County, they are in nine lakes. In Allen County, they are in the St. Joseph River and the Cedarville Reservoir.

In 2010 the city of Fort Wayne was aware of the mussels. The city has intakes for the water system located in the reservoir and river. Mary Jane Slaton, spokeswoman for City Utilities, said so far the mussels have not caused a problem, although this fall they will be diving to check intake entrances.

The plankton-eating mollusks clear the water and reproduce quickly. One female can lay a million eggs in a single breeding season. The result has been the clogging of city water systems up and down the Great Lakes, and massive blooms of blue-green algae. High concentrations of certain species of blue-green algae can be toxic. Since their appearance in the Great Lakes, zebra mussels have spread all the way to California.

By wiping out plankton, mussels have affected the food chain enough that sport-fishing in the Great Lakes has dropped off as the smaller fish that rely on plankton for food have declined.

Author Jeff Alexander has documented this transformation of the Great Lakes in his book, “Pandora's Locks: The Opening of the Great Lakes-St. Lawrence Seaway,” which traces the ecological disaster invasive species have caused since the St. Lawrence Seaway opened in 1959.

Invaders' toll

The decline in game fish in the Great Lakes cannot be totally blamed on the zebra mussels or their bigger cousin, the quagga mussel. There have been other invasive species of fish, like the Eurasian ruffe and the tubenose and round goby. Sea lampreys first discovered in 1921 in Lake Erie began the destruction. By the 1950s the lampreys had decimated the lake trout fisheries in lakes Michigan, Huron and Superior. Northern Indiana lakes have yet to see any of these fish species, but the first zebra mussels appeared in Lake Wawasee in 1991.

Warren Pryor, associate professor of biology at University of Saint Francis and a specialist in freshwater mussels, said that if you look at the lakes as valleys, the zebra mussel has been the first invasive species able to climb out of the valley and down the slopes into the lakes of northern Indiana. He says it is almost impossible to foretell the impact of the mussels in northern Indiana lakes.

“There are just so many variables, it's very hard to predict,” Pryor said.

According to Doug Keller, aquatic invasive species coordinator for the Indiana Department of Fish and Wildlife, there are still a healthy number of game fish to be found in Wawasee. However, as the zebra mussels eat the plankton, sunfish, which rely on plankton for food, will decrease. Sunfish are a food source for bass and so bass will also decline. Weeds also will become more common as the sunlight reaches further down in the clear water. This will give the sunfish more places to hide, making them harder for the bass to catch.

“Don't let anyone tell you there is anything good about the zebra mussel; this is a huge ecological disaster,” said G. Thomas Watters, mollusk curator at Ohio State University.

How fish are harmed

Watters, a specialist in native mussels, said the zebra mussels can be destructive for fish that spawn on the bottom. The zebra mussels move in and there is nowhere for the fish to lay their eggs. As for native freshwater mussels, the zebra mussel, which is considerably smaller than a native mussel, will attach itself to the shell, depriving the mussel of its ability to filter the water for food, starving the mussel. Zebra mussels do have a predator here, the freshwater drum. In Asia the primary predator is a diving duck species.

This spring the DNR began checking the size of muskie in Lake Webster. Anglers have been complaining fewer are reaching trophy size, 46 inches. It is too early to say why this would be, but muskie tend to spawn in shallow water along the edge of lakes. Zebra mussels generally can be found in the shallows out to 100 feet from the shoreline.

For Jim Gnagy, owner of Hamilton Lake Marine for the past 44 years, mussels are a headache for boaters in the area. They clog intake valves on outboard and inboard motors and adhere to the hulls of boats left in the water. Gnagy said the shells are so sharp that when his grandchildren come to visit, they must wear water shoes on the beach so they don't cut their feet. He says mollusks are first seen around the public boat landings. Then they are carried from one lake to another as larvae in the cooling tanks of boats.

“Two years ago, they were this thick on my shore station,” Gnagy said, holding his fingers three inches apart. For the past two years, he said he has seen a drop in the number.

Another predator found?

Recently Gnagy was talking to a friend who fishes Lake Hamilton and had caught several redear sunfish over the weekend. His friend said that when he cleaned the fish he discovered they were loaded with zebra mussels.

“Maybe that's why I'm not seeing as many,” Gnagy said.

To prevent the spread of zebra mussels or other invasive species, Keller recommends boaters drain all bilge water from their boats' tanks before placing them in other bodies of water. Boaters also should let the boat sit out of the water for at least five days so any organism on the outside of the hull dies.

Keller said blue-green algae – a byproduct of clearer water, is being monitored in several areas around the state. According to the Indiana Department of Environmental Management website, a high level of the algae can cause a bad taste and odor in drinking water. As the algae dies off, it sinks to the bottom, absorbing the oxygen in the water. This can cause fish kills. The algae also can cause sickness or death in animals and livestock, but this has never happened in Indiana. Of the 50 types of blue-green algae, only a third can cause illness. In Indiana, that algae group is Cyanophyta. So far, that hasn't been reported locally.