New species invades harbor

The good news is that the Twin Ports' population of invasive zebra mussels could be wiped out of the harbor and lower St. Louis River in a matter of years.

The good news is that the Twin Ports' population of invasive zebra mussels could be wiped out of the harbor and lower St. Louis River in a matter of years.

The bad news is that the thumbnail-sized invaders from northern Europe will be eradicated and replaced by another invading mussel that could prove even worse for underwater ecosystems.

The U.S. Environmental Protection Agency is expected to announce next week that quagga mussels have been found in the Twin Ports, exotic species experts confirmed. It is the first such finding on Lake Superior.

Quaggas are a slightly larger cousin of zebra mussels. Quaggas originated in coastal areas of Ukraine but now have spread across much of Europe. They have been in the Great Lakes since 1989 but have exploded in numbers over the past six years.

As with many new invaders, it's not clear what effect quaggas will have when they take hold here. But they already are proving a big problem in the lower Great Lakes.


While zebra mussels inhabit shallow waters of less than 150 feet, quaggas have been found thriving 500 feet deep. Quaggas also can withstand colder water and can thrive with less food, said Tom Nalepa, a biologist for the National Oceanic and Atmospheric Administration's Great Lakes Environmental Research Laboratory in Ann Arbor, Mich.

That might seem to make Lake Superior a prime spot for quaggas. But outside harbors, the big lake's extremely low calcium levels probably will prevent a quagga invasion in the main lake. That's good news for lake trout and other open-water species. Calcium is critical for shell development.

EPA officials didn't return calls on the Twin Ports quagga finding. Other experts warned of what quaggas have done in other Great Lakes with higher calcium levels.

"We know they [quagga mussels] can thrive in much deeper, colder water and that they need less food to be successful. But I don't think they will expand in open water of Lake Superior because of the low calcium levels there,'' Nalepa said. "They require less calcium than zebra mussels, they have softer shells, but they still need more than Lake Superior has to offer.''

Mary Balcer, an exotic species expert at the University of Wisconsin-Superior, agreed. She said harbor and river calcium levels are just enough to sustain the exotic mussels, while Lake Superior calcium levels are too low.

"I don't expect to see a major impact in [deep-water] areas of Lake Superior because of the calcium,'' Balcer said. "I don't think we'll see as much ecological impact as other areas have seen'' when quaggas replace zebra mussels in the Twin Ports.


Quaggas already have replaced zebra mussels in lakes Erie, Michigan and Huron and are causing more problems than zebras in those lakes.


In Lake Michigan, quaggas comprised only 2 percent of the exotic mussels in 2000. By 2005, they hit 98 percent, virtually eliminating zebra mussels. Because they can thrive on deeper, soft-bottom areas of the lakes, not just rocks and hard surfaces, there are more quaggas in more places than zebra mussels ever colonized.

Experts say quaggas may end up being a much bigger problem. They already have caused lakes Michigan and Huron to be much clearer than any time in recent history -- because the mussels filter tiny organisms out of the water for their food.

"There is just so much more biomass out there now with quaggas than we had with zebra mussels. It's a big difference,'' Nalepa said, noting that Lake Huron has seen drastic changes since quaggas replaced zebras. That includes a huge reduction in the amount of tiny plankton available for native fish, a reduction in baitfish and even a collapse of alewife populations. That has caused trout and salmon to be become skinnier.

Because of the decline in baitfish, Michigan officials have cut their salmon stocking efforts in half on Lake Huron. Officials fear Lake Michigan fish may crash as well.

In Lake Michigan, numbers of tiny, native shrimp called diporeia, a critical food species for fish, have declined dramatically from 5,200 per square meter in 1995 to 1,800 in 2000. The decline came even faster with quaggas, with only 300 diporeia per square meter by 2005.

That may be why the average size of a 7-year-old native whitefish has declined from 5 pounds to about 1.5 pounds in Lake Michigan. Fish try to eat quaggas, but spend more energy to digest them and don't gain weight.


It's not just what they eat and how much energy quaggas take out of the food chain, but the quagga's feces also build up and foul the environment As that waste decomposes, it uses oxygen and the water becomes acidic. Moreover, quaggas will continue to kill off native mussels. Quaggas accumulate organic pollutants, such as mercury, in their tissue to levels 300,000 times greater than the water around them, according to the U.S. Geological Service. They then pass those contaminants on to whatever eats them.


Zebra mussels first were found in the Twin Ports in 1989 but didn't expand here until 1998. Scientists aren't sure why it took a decade for them to begin to survive winters and reproduce here, but their ultimate success may be linked to higher temperatures in the past decade. Zebra mussels now cover most of the hard surfaces in the harbor and lower St. Louis River.

Efforts are under way to educate boaters so the mussels aren't accidentally spread to inland lakes in bait buckets and boat bilges or live wells. In all areas where the mussels have colonized, they have fouled water intake systems and covered underwater pilings and mechanisms, requiring constant removal.

It's believed zebra and quagga mussels traveled to the Great Lakes in the ballast water of oceangoing ships. Efforts are under way to develop technology to treat ballast water to kill invasive species. It's expected Congress will move soon to further curtail invasive species. A federal judge has ordered the EPA to regulate ballast water starting in 2008.

John Myers reports on the outdoors, natural resources and the environment for the Duluth News Tribune. You can reach him at
What To Read Next
Get Local