Great Lakes Article:

Tiny lake creatures are falling victim to strange lesions

06/05/02

Abnormal lesions that resemble tumors are appearing on the shells of flea-sized crustaceans in the Great Lakes, and scientists now fear an unknown pestilence is attacking a crucial link in the freshwater food chain.

Eventually, the lesions are fatal to the tiny creatures known as zooplankton, which are the primary food source for young salmon, yellow perch, walleye and trout.

A National Oceanographic and Atmospheric Administration report that summarizes existing knowledge about the mysterious ailment calls it "a serious, emerging threat to the food web."

The largest of the zooplankton are one-eighth of an inch long. Somehow, the small creatures' muscles, guts or gonads get outside their shells, growing externally. One scientist studying the phenomena said it looks as if "internal tissue tends to leak out of the animal. When you have a lot of tissue leaking out, you're dead."

The outbreak of the lesions has quickly appeared, then disappeared, from sampling locations across all five Great Lakes. There is concern that shoreline tourism and fishing economies may be devastated if the zooplankton supply collapses. There is no evidence that the phenomenon has any adverse effects on humans.

Federal researchers for three years have been tracking the slow spread of the strange protrusions that were first discovered on Lake Michigan zooplankton. As yet, they have not been able to pinpoint the perpetrator.

Throughout this summer, a U.S. EPA research vessel, the 180-foot Lake Guardian, will be cruising the lakes collecting samples for scientists.

To capture plankton, the ship drags cones of white cloth that are up to 10 feet long. The Lake Guardian will spend several days in Lake Erie this month, and is expected to visit Cleveland by mid-June.

Researchers have found that predatory species of zooplankton - those that eat other animals - are more likely to have the growths than those eating vegetation. The abnormal growths are more common near the shore than off shore.

"On a human, it would look like a beach ball-sized hump growing out of their body," said Tom Bridgeman, an aquatic biologist at the Lake Erie Center, an Ohio research laboratory at Maumee Bay State Park in the Toledo suburb of Oregon.

"When you see it, it's hard to imagine that a plankton could even live with these things attached."

Researchers are not sure if the mysterious outbreak is a type of cancer, an unknown infectious disease, a previously unseen parasite or a reaction to years of industrial pollution. Nor can they forecast how severe the threat may be.

Some scientists studying the problem worry it could be a rogue pest that hitchhiked into the Great Lakes in the ballast water of an oceangoing freighter, the same route taken by zebra mussels in the 1980s.

Other theories are that the tumor-like lesions could be related to the start of global climate changes that may be affecting the Midwest.

In recent years, ice sheets have not covered the Great Lakes because of mild winters.

Another theory holds that the abnormal growths may be brought about by extra sunlight streaming into lake water. Just a decade ago, the water was murky and sunlight did not penetrate very far into the depths. But that was before zebra mussels dramatically altered the marine environment by filtering and clarifying the Great Lakes.

"There are plenty of theories, no answers," said Henry A. Vanderploeg, a frustrated research ecologist at NOAA's Great Lakes Environmental Research Laboratory in Ann Arbor, Mich.

"We all see these tumor-like growths and lesions, but nobody knows what's causing them. It's sort of a scientific nightmare."

Vanderploeg said he doesn't like to discuss the tumor-like growths.

"It could be serious, but until we know what the heck is going on, I'm reluctant to speculate."

Gretchen Messick, a pathologist at an NOAA lab in Maryland, said she has been studying the growths and does not believe they are malignant tumors.

"If we could find out what it is, we could determine if there's a new organism out there invading the waters," Messick said. "At this point, I can't really say how it got there, or whether it has been there before, or whether it's come in by shipping."

Initially, the growths were found on plankton collected at a few sampling sites in Lake Michigan. By last fall, their existence was confirmed in Lake Erie and Lake Ontario.

Bridgeman, the Ohio researcher, said the culprit causing the growths could be a microscopic parasite. He said the parasites, which he found in an inland lake near Ann Arbor, Mich., 20 months ago, puncture the zooplankton shells and absorb the bodily fluids.

Bridgeman said cleaning up the lakes may have freed up the parasites to go on the attack. "Our lakes have been polluted so long, it's possible the pollution acted like a barrier," he said.

But Messick, the NOAA scientist, said the problem is not parasites.

"I have found parasites on some of them, but the presence of parasites is pretty low, less than 10 percent," she said. "The others . . . well, we just don't know. But it's not parasites."

Mohamad Omair, a fisheries researcher at the University of Michigan's Center for Great Lakes and Aquatic Sciences, said research at his lab has led scientists to believe the growths are actual tumors. He disagrees with the Bridgeman's parasite theory.

"The Smithsonian Institution sent samples that were collected in Lake Superior in the 1880s. They had parasites. This is a different abnormal growth," Omair said. "Is it a bug? A chemical? I don't know. All I know is that it's a reaction to something. This is a wake-up call that we have an unknown problem in the Great Lakes."

A NOAA research publication seems to agree.

"Whatever the mysterious culprit is, it must be like something right out of a Stephen King novel for these tiny, shrimp-like creatures. Just imagine waking up one morning to find that something had burrowed a hole through your skin, causing your innards to balloon out into a cyst the size of your head."