U.S. Biologists Seek Ways to Stop Alien Mussel Invasion

Environmental News Network
September 24, 2001
It took less than ten years. Non-native zebra mussels from Europe first
appeared in the Mississippi River in 1991, and today the exploding zebra
mussel population has carpeted some parts of the Mississippi River bed
with 10,000 to 20,000 mussels per square yard.

Spread largely in
bilge water of commercial Mississippi River barge traffic, the mussels'
hard shells can cut humans, dogs, and other animals that come in contact
with them. Zebra mussels are the only freshwater mollusks that can
attach themselves to solid objects such as submerged rocks, dock
pilings, and boat hulls. They can clog intake pipes at power plants and
require expensive treatments to remove them.

Native mussel species are the losers in this war. Almost 70 percent of the nation's 297 native mussel species are endangered, threatened, or potentially warrant federal protection. Zebra mussels have decimated native mussel species along the Mississippi and pushed the Higgins' eye pearly mussel to the brink of extinction.

Not only do the zebra mussels compete with the native mussels for food, they attach to their shells, preventing their reproduction and smothering them, according to Ron Benjamin, who works with the Wisconsin Department of Natural Resources as fisheries supervisor for the Mississippi River.

Recently crews from Wisconsin, Iowa, and the federal government fanned out along a 500-mile (800-kilometer) stretch of the Mississippi River to look for zebra mussels and clues about how to fight this exotic invasive species and save the native species.

They used bilge pumps and buckets to collect water samples that will be analyzed at an Illinois laboratory for veligers, the microscopic, larval form of zebra mussels. One cup of river water can contain as many as 100 of these young invaders.

"We're trying to study how veligers are distributed in the river, where they settle, how they fare from year to year, and what they do to an ecosystem over time," said John Sullivan, a Wisconsin Department of Natural Resources water-quality specialist for the Mississippi River. "We're in the infancy of studying zebra mussels and how they affect our ecosystems."

Broad-Based Effort

This is the fourth year crews have looked for the veligers. They are part of a larger effort to understand and cope with the invading mollusks that includes the U.S. Army Corps of Engineers, the U.S. Fish & Wildlife Service, and other state agencies.

A native of eastern Europe and western Asia, the thumbnail-size zebra mussels were first discovered in U.S. waters in 1988. They likely arrived in the ballast of ocean-going vessels that emptied their tanks in Great Lakes ports.

Today zebra mussels have spread to all of the Great Lakes and major river systems in the Midwest, moving through waterways by attaching to boats and barges.

This spring, biologists with the U.S. Fish and Wildlife Service and the Minnesota and Wisconsin Natural Resource Departments began working to bring the federally endangered Higgins' eye pearly mussel back from extinction.

Since May, scuba divers and groups of workers armed with syringes and plastic buckets have been collecting Higgins' eye pearly mussels. They intend to produce young Higgins' eyes at the service's Genoa National Fish Hatchery in Genoa, Wisconsin, for eventual release back into their natural habitat.

"Our goal with the hatchery project is to take adult Higgins' eye mussels from areas already infested with zebra mussels, raise young mussels in the hatchery, and then release them in areas where they should be safe from that threat," said Pam Thiel, fisheries biologist with the Fish and Wildlife Service. "We hope we can keep this species going in the hatchery and in some remaining suitable natural habitats to prevent zebra mussels from eliminating the Higgins' eye."

Fisheries supervisor Benjamin said "Zebra mussels have the ability to impact our ecosystems. They like the algae [that] fish like, so they're competing with our fish for food. But they don't like the blue-green algae that can foul many lakes and rivers, and in fact, they're adding to the problem because they release ammonia- and phosphorus-containing waste products that may fuel blue-green algae blooms."

In fact, respiratory demand and waste products released by 30 acres (12 hectares) of zebra mussels requires roughly the same amount of dissolved oxygen required to break down the organic material discharged by the Twin Cities Metropolitan Wastewater Treatment Plant, water-quality specialist Sullivan said.

That oxygen demand contributed to unusually low dissolved oxygen concentrations in portions of the Mississippi River during the early summer periods of 1997 and 1998, stirring fears of fish kills.

Caution Urged

This summer's sampling for larval zebra mussels is important in helping verify that the relocated native mussels are living in hospitable sites. The sampling involved collecting water from below the locks and dams stretched along the 500 miles (800 kilometers) from the Hastings Dam below St. Paul, Minnesota, to Keokuk, Iowa, and on large tributaries, including the Chippewa, the Black, the Wisconsin, and the St. Croix, Sullivan said.

These hard-working biologists are warning people to clean their boats and trailers carefully to prevent zebra mussels from moving into new lake and riverine systems. Larvae can be carried in bilge water, bait buckets, and fish holds. Adults can easily hitch a ride on the bottom of boat hulls or on barges.

Fisheries experts have set up two experimental projects to relocate vanishing native mussel species to parts of the Upper Mississippi River with lower zebra mussel densities.

Benjamin said, "We need to find a place to move enough mussel species out of harm's way so (that) if we ever do get a handle on zebra mussels and how to control them, we have the genetic material to put the ecosystem back together."

Fisheries authorities on the West Coast are alert to the possibility that zebra mussels may have reached the Columbia River. The U.S. Coast Guard and the Fish and Wildlife Service, working closely with the office of U.S. Senator Ron Wyden of Oregon, have released U.S. $275,000 for a three-year study of aquatic nuisance species in the lower Columbia River.

The Columbia River is considered to be at risk for invasion by potentially damaging non-native species such as zebra mussels.

The study will be conducted by the Pacific States Marine Fisheries Commission in collaboration with Portland State University, the University of Washington, and Oregon State University.

Copyright 2001 Environmental News Network

Story Two: Stowaway U.S. Corn Rootworm Eats Its Way Across Europe Go>>

Story Three: Australian Bug Imported to Fight Pesky Plant in U.S. Everglades Go>>

Return to first page of this series. Go>>

© 1996-2008 National Geographic Society. All rights reserved.