Lesions Taking Toll On Tiny Great Lakes Crustaceans

CLEVELAND (AP) - Abnormal lesions are taking a toll on tiny crustaceans that are a key part of the Great Lakes food chain, scientists said.

The lesions can kill zooplankton, which are up to one-eighth of an inch long and the primary food source for young salmon, yellow perch, walleye and trout.

A National Oceanographic and Atmospheric Administration report called it "a serious, emerging threat to the food web."

The outbreak of the lesions has quickly appeared, then disappeared, from sampling locations across the five Great Lakes, The Plain Dealer reported Wednesday.

There is no evidence that the phenomenon has adverse effects on humans.

Researchers for three years have been tracking the spread of the lesions first discovered on Lake Michigan zooplankton. The cause hasn't been determined.

During the summer a U.S. Environmental Protection Agency research vessel, the 180-foot Lake Guardian, will cruise the lakes collecting samples.

Researchers have found that predatory species of zooplankton that eat other animals are more likely to have the growths than those eating vegetation. Lesions are more common near the 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, a research laboratory at Maumee Bay State Park near Toledo. "When you see it, it's hard to imagine that a plankton could even live with these things attached."

Researchers are unsure if the outbreak is a type of cancer, an unknown infectious disease, a previously unseen parasite or a reaction to pollution.

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

Another theory holds that the lesions could be related to climate changes. In recent mild winters ice sheets have not covered the lakes.

Another theory holds that the lesions may be caused by extra sunlight streaming into lake water in recent years since zebra mussels filtered and clarified it. Before the water was murky.

"There are plenty of theories, no answers," said Henry A. Vanderploeg, a 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."

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.

(Copyright 2002 by The Associated Press. All Rights Reserved.)