Scientists Study Link Between Zebra Mussels And Algae Blooms

Once a lake is infested with zebra mussels, an unusual bloom of blue-green algae scum called microcystis often follows. Zebra mussels invade lakes most used by people, and microcystis can produce toxins potentially harmful to wildlife and people.

MSU's Stephen Hamilton, an assistant professor of zoology at the Kellogg Biological Station, along with Orlando Sarnelle, assistant professor of fisheries and wildlife, this month begin a study to confirm the link between mussels and microcystis. It's the first step in understanding the impact of the mollusks and how it will affect those that use the lakes.

"We think the inland lakes are going through tremendous ecological changes," Hamilton said. "We need to understand how these lakes change when the mussels get in."

Zebra mussels are an exotic species that traveled from the Black Sea to the Great Lakes in the early 1980s by hitching a ride on a ship. The same method of transportation has brought them increasingly to inland lakes both in the Midwest and across the country. The hard-shelled creatures cling in clumps, have no natural predators and multiply rapidly.

Recreational lakes have born the brunt of the first invasion because the mussels and their eggs travel on small amounts of water in sport and fishing boats. According to Michigan Sea Grant, the presence of zebra mussels has been confirmed in at least 75 inland lakes throughout the state.

The mussels eat virtually everything they can filter - except for microcystis, which they spit out. The theory is that the mussels help foster a blue-green algae bloom by reducing competing algae.

That can mean trouble. Microcystis actually is a bacterium. It occurs naturally in most lakes at low concentrations. But large blooms are cropping up in lakes that don't normally have them.

When large concentrations of microcystis occur the water has a bright bluish-green or yellow-green color. This dramatic coloration has been described as looking like a paint spill on the water's surface. Several algae blooms have been reported to state and local emergency response agencies as paint spills, said David Wade, Ph.D. toxicologist for the Michigan Department of Community Health division of environmental epidemiology.

Hamilton and Sarnelle, along with graduate students David Raikow and Alan Wilson, will be surveying inland lakes known to have zebra mussels as well as lakes that don't to confirm the link between the occurrence of zebra mussels and the microcystis blooms. Next summer, the team plans an experiment in which they will install a series of giant, plastic bags in a lake that already has zebra mussels. The bags will be stocked with varying densities of the mussels to observe their effects on microcystis blooms.

"Zebra mussels have been studied for more than 10 years in the Great Lakes, but now we have to look at the impact on inland lakes, because it's a very different scenario," Hamilton said. "We don't know what they'll do in inland lakes."

So far, there never have been reports of people in Michigan becoming ill from exposure to microcystis. But caution is warranted.

"There is very little health risk if people avoid direct contact with the bloom," Wade said. "Still, it's nasty looking and nasty smelling."