Invasive Species in Lake Michigan

We all know about zebra mussels but there are other invasive species in Lake Michigan. This article for the Tribune discusses some of the species and the changes they are causing.

Underwater, a disturbing new world

A Tribune team follows researchers to the bottom of Lake Michigan as they try to explain the rapidly shifting ecosystem

By James Janega | Chicago Tribune reporter

July 30, 2008

OFF ATWATER BEACH, Wis.—This place should be an underwater desert.

But as the three researchers wearing scuba tanks and lead weights drop through the water, the landscape of rounded stones 30 feet below is disturbingly full of strange, new life.

In just a few years, the gravel and white boulders that for centuries covered the bottom of Lake Michigan between Chicago and the Door County, Wis., peninsula have disappeared under a carpet of mussels and primitive plant life.

The change is not merely cosmetic. In the last three years or so, scientists say, invasive species have upended the ecology of the lakes, shifting distribution of species and starving familiar fish of their usual food supply.

Signs of the shift have been hard to ignore. Mats of dead, smelly algae wash ashore on Lake Michigan from Chicago to the Straits of Mackinac, castoffs of a vast underwater expanse seen from boat decks and from hilltops at Sleeping Bear Dunes in Michigan. Fishermen haul it up in their nets, dubbing it "lake moss."

Multiple strains of E. coli bacteria and botulism spores thrive in the new underwater garden, leading scientists to suspect they are contributing to beach closings and the widespread deaths of migratory birds. Meanwhile, fishermen notice the lake trout, salmon and whitefish are getting skinnier each season.

The rapid shift has researchers scrambling to understand what is happening and how widely the impact will be felt.

"The lake is changing faster than we can study it," said University of Wisconsin-Milwaukee researcher Harvey Bootsma, whose small team of researchers hunts explanations from this new lake bottom in weekly dives off the Wisconsin shore.

Adaptation possible

Some ecologists and fishery managers say the Great Lakes may adapt, noting that some fish seem to be eating the most common invasive species. But experts also say the species are fueling change in the lakes at a rate far faster than they have ever seen.

"We don't necessarily know all the impacts, but we know enough to know that they are being catastrophic," said Cameron Davis, president of the Alliance for the Great Lakes. "The ecological balance of the Great Lakes is at a tipping point. And the question is: Can they recover? Or can we act quickly enough to help them recover?"

None of the key species leading the change—mussels, algae and round gobies—are new arrivals. The zebra mussel famously invaded Lake Michigan two decades ago, and its cousin, the quagga mussel, wasn't far behind.

But in the last handful of years the quagga has taken off with alarming speed, exploding across the lake floor.

While zebra mussels like to attach themselves to rocks and man-made structures, the quaggas can colonize sandy bottoms deeper in the lakes. Between them, the species filter lake water ceaselessly, making it so crystal clear that light can penetrate far deeper than before.

That change has allowed a native species of algae called cladophora to run rampant. It now can grow in 30 feet of water, twice as deep as a decade ago, and its waving tendrils cover vast offshore areas.

Round gobies, an invasive fish species from the Black Sea willing to eat the mussels, love this new environment. They breed prolifically and are now the most abundant fish species found in many parts of the lake.

Together, these species have not only altered the clarity of the water but also devoured and filtered out the nutrients that used to sustain plankton and shrimplike diporeia at the base of the lake's food chain, starving what larger fish are left.

To be sure, the Great Lakes ceased to be a wholly native ecosystem long ago. Atlantic alewives sneaked into the lakes in 1873. People began stocking rainbow trout and chinook salmon shortly after the alewives, and added brown trout and coho salmon to the mix by 1933.

By the 1950s, the most important fish in the native food chain—lake trout, ciscoes and spiny sculpins—were nearly gone in the lower lakes and severely reduced in Lakes Michigan and Huron. Still, scientists say perch, salmon and the alewives on which they foraged formed a relatively stable ecosystem until the invasive mussels began devouring key microscopic nutrients.

"Now all the forage fish are way down in Lake Michigan and Lake Huron," said Henry Vanderploeg, a Great Lakes ecologist for the National Oceanic and Atmospheric Administration. "There's a crisis. The mussels are really messing up the food chain."

It's possible fish will weather the changes. Fishermen have caught lake trout that had gobies in their stomachs, and smallmouth bass in Lake Erie have doubled their size in 10 years by feasting on gobies, said Marc Gaden, spokesman for the Great Lakes Fisheries Commission.